1.
Crystal
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A crystal or crystalline solid is a solid material whose constituents are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macroscopic single crystals are usually identifiable by their geometrical shape, the scientific study of crystals and crystal formation is known as crystallography. The process of crystal formation via mechanisms of crystal growth is called crystallization or solidification, the word crystal derives from the Ancient Greek word κρύσταλλος, meaning both ice and rock crystal, from κρύος, icy cold, frost. Examples of large crystals include snowflakes, diamonds, and table salt, most inorganic solids are not crystals but polycrystals, i. e. many microscopic crystals fused together into a single solid. Examples of polycrystals include most metals, rocks, ceramics, a third category of solids is amorphous solids, where the atoms have no periodic structure whatsoever. Examples of amorphous solids include glass, wax, and many plastics, Crystals are often used in pseudoscientific practices such as crystal therapy, and, along with gemstones, are sometimes associated with spellwork in Wiccan beliefs and related religious movements. The scientific definition of a crystal is based on the arrangement of atoms inside it. A crystal is a solid where the form a periodic arrangement. For example, when liquid water starts freezing, the change begins with small ice crystals that grow until they fuse. Most macroscopic inorganic solids are polycrystalline, including almost all metals, ceramics, ice, rocks, solids that are neither crystalline nor polycrystalline, such as glass, are called amorphous solids, also called glassy, vitreous, or noncrystalline. These have no periodic order, even microscopically, there are distinct differences between crystalline solids and amorphous solids, most notably, the process of forming a glass does not release the latent heat of fusion, but forming a crystal does. A crystal structure is characterized by its cell, a small imaginary box containing one or more atoms in a specific spatial arrangement. The unit cells are stacked in three-dimensional space to form the crystal, the symmetry of a crystal is constrained by the requirement that the unit cells stack perfectly with no gaps. There are 219 possible crystal symmetries, called space groups. These are grouped into 7 crystal systems, such as cubic crystal system or hexagonal crystal system, Crystals are commonly recognized by their shape, consisting of flat faces with sharp angles. Euhedral crystals are those with obvious, well-formed flat faces, anhedral crystals do not, usually because the crystal is one grain in a polycrystalline solid. The flat faces of a crystal are oriented in a specific way relative to the underlying atomic arrangement of the crystal. This occurs because some surface orientations are more stable than others, as a crystal grows, new atoms attach easily to the rougher and less stable parts of the surface, but less easily to the flat, stable surfaces
2.
Rock (geology)
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Rock or stone is a natural substance, a solid aggregate of one or more minerals or mineraloids. For example, granite, a rock, is a combination of the minerals quartz, feldspar. The Earths outer solid layer, the lithosphere, is made of rock, rock has been used by mankind throughout history. The minerals and metals found in rocks have been essential to human civilization, three major groups of rocks are defined, igneous, sedimentary, and metamorphic. The scientific study of rocks is called petrology, which is a component of geology. At a granular level, rocks are composed of grains of minerals, the aggregate minerals forming the rock are held together by chemical bonds. The types and abundance of minerals in a rock are determined by the manner in which the rock was formed, many rocks contain silica, a compound of silicon and oxygen that forms 74. 3% of the Earths crust. This material forms crystals with other compounds in the rock, the proportion of silica in rocks and minerals is a major factor in determining their name and properties. Rocks are geologically classified according to such as mineral and chemical composition, permeability, the texture of the constituent particles. These physical properties are the end result of the processes that formed the rocks, over the course of time, rocks can transform from one type into another, as described by the geological model called the rock cycle. These events produce three general classes of rock, igneous, sedimentary, and metamorphic, the three classes of rocks are subdivided into many groups. However, there are no hard and fast boundaries between allied rocks, hence the definitions adopted in establishing rock nomenclature merely correspond to more or less arbitrary selected points in a continuously graduated series. Igneous rock forms through the cooling and solidification of magma or lava and this magma can be derived from partial melts of pre-existing rocks in either a planets mantle or crust. Typically, the melting of rocks is caused by one or more of three processes, an increase in temperature, a decrease in pressure, or a change in composition, igneous rocks are divided into two main categories, plutonic rock and volcanic. Plutonic or intrusive rocks result when magma cools and crystallizes slowly within the Earths crust, a common example of this type is granite. Volcanic or extrusive rocks result from magma reaching the surface either as lava or fragmental ejecta, the chemical abundance and the rate of cooling of magma typically forms a sequence known as Bowens reaction series. Most major igneous rocks are found along this scale, about 64. 7% of the Earths crust by volume consists of igneous rocks, making it the most plentiful category. Of these, 66% are basalts and gabbros, 16% are granite, only 0. 6% are syenites and 0. 3% peridotites and dunites
3.
Mineral
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A mineral is a naturally occurring chemical compound, usually of crystalline form and abiogenic in origin. A mineral has one specific chemical composition, whereas a rock can be an aggregate of different minerals or mineraloids, the study of minerals is called mineralogy. There are over 5,300 known mineral species, over 5,070 of these have been approved by the International Mineralogical Association, the silicate minerals compose over 90% of the Earths crust. The diversity and abundance of species is controlled by the Earths chemistry. Silicon and oxygen constitute approximately 75% of the Earths crust, which translates directly into the predominance of silicate minerals, minerals are distinguished by various chemical and physical properties. Differences in chemical composition and crystal structure distinguish the various species, changes in the temperature, pressure, or bulk composition of a rock mass cause changes in its minerals. Minerals can be described by their various properties, which are related to their chemical structure. Common distinguishing characteristics include crystal structure and habit, hardness, lustre, diaphaneity, colour, streak, tenacity, cleavage, fracture, parting, more specific tests for describing minerals include magnetism, taste or smell, radioactivity and reaction to acid. Minerals are classified by key chemical constituents, the two dominant systems are the Dana classification and the Strunz classification, the silicate class of minerals is subdivided into six subclasses by the degree of polymerization in the chemical structure. All silicate minerals have a unit of a 4− silica tetrahedron—that is, a silicon cation coordinated by four oxygen anions. These tetrahedra can be polymerized to give the subclasses, orthosilicates, disilicates, cyclosilicates, inosilicates, phyllosilicates, other important mineral groups include the native elements, sulfides, oxides, halides, carbonates, sulfates, and phosphates. The first criterion means that a mineral has to form by a natural process, stability at room temperature, in the simplest sense, is synonymous to the mineral being solid. More specifically, a compound has to be stable or metastable at 25 °C, modern advances have included extensive study of liquid crystals, which also extensively involve mineralogy. Minerals are chemical compounds, and as such they can be described by fixed or a variable formula, many mineral groups and species are composed of a solid solution, pure substances are not usually found because of contamination or chemical substitution. Finally, the requirement of an ordered atomic arrangement is usually synonymous with crystallinity, however, crystals are also periodic, an ordered atomic arrangement gives rise to a variety of macroscopic physical properties, such as crystal form, hardness, and cleavage. There have been recent proposals to amend the definition to consider biogenic or amorphous substances as minerals. The formal definition of an approved by the IMA in 1995, A mineral is an element or chemical compound that is normally crystalline. However, if geological processes were involved in the genesis of the compound, Mineral classification schemes and their definitions are evolving to match recent advances in mineral science
4.
Latin
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Latin is a classical language belonging to the Italic branch of the Indo-European languages. The Latin alphabet is derived from the Etruscan and Greek alphabets, Latin was originally spoken in Latium, in the Italian Peninsula. Through the power of the Roman Republic, it became the dominant language, Vulgar Latin developed into the Romance languages, such as Italian, Portuguese, Spanish, French, and Romanian. Latin, Italian and French have contributed many words to the English language, Latin and Ancient Greek roots are used in theology, biology, and medicine. By the late Roman Republic, Old Latin had been standardised into Classical Latin, Vulgar Latin was the colloquial form spoken during the same time and attested in inscriptions and the works of comic playwrights like Plautus and Terence. Late Latin is the language from the 3rd century. Later, Early Modern Latin and Modern Latin evolved, Latin was used as the language of international communication, scholarship, and science until well into the 18th century, when it began to be supplanted by vernaculars. Ecclesiastical Latin remains the language of the Holy See and the Roman Rite of the Catholic Church. Today, many students, scholars and members of the Catholic clergy speak Latin fluently and it is taught in primary, secondary and postsecondary educational institutions around the world. The language has been passed down through various forms, some inscriptions have been published in an internationally agreed, monumental, multivolume series, the Corpus Inscriptionum Latinarum. Authors and publishers vary, but the format is about the same, volumes detailing inscriptions with a critical apparatus stating the provenance, the reading and interpretation of these inscriptions is the subject matter of the field of epigraphy. The works of several hundred ancient authors who wrote in Latin have survived in whole or in part and they are in part the subject matter of the field of classics. The Cat in the Hat, and a book of fairy tales, additional resources include phrasebooks and resources for rendering everyday phrases and concepts into Latin, such as Meissners Latin Phrasebook. The Latin influence in English has been significant at all stages of its insular development. From the 16th to the 18th centuries, English writers cobbled together huge numbers of new words from Latin and Greek words, dubbed inkhorn terms, as if they had spilled from a pot of ink. Many of these words were used once by the author and then forgotten, many of the most common polysyllabic English words are of Latin origin through the medium of Old French. Romance words make respectively 59%, 20% and 14% of English, German and those figures can rise dramatically when only non-compound and non-derived words are included. Accordingly, Romance words make roughly 35% of the vocabulary of Dutch, Roman engineering had the same effect on scientific terminology as a whole
5.
Glass
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Glass is a non-crystalline amorphous solid that is often transparent and has widespread practical, technological, and decorative usage in, for example, window panes, tableware, and optoelectronics. The most familiar, and historically the oldest, types of glass are silicate glasses based on the chemical compound silica, the primary constituent of sand. The term glass, in usage, is often used to refer only to this type of material. Many applications of silicate glasses derive from their optical transparency, giving rise to their use as window panes. Glass can be coloured by adding metallic salts, and can also be painted and printed with vitreous enamels and these qualities have led to the extensive use of glass in the manufacture of art objects and in particular, stained glass windows. Although brittle, silicate glass is extremely durable, and many examples of glass fragments exist from early glass-making cultures, because glass can be formed or moulded into any shape, it has been traditionally used for vessels, bowls, vases, bottles, jars and drinking glasses. In its most solid forms it has also used for paperweights, marbles. Some objects historically were so commonly made of glass that they are simply called by the name of the material, such as drinking glasses. Porcelains and many polymer thermoplastics familiar from everyday use are glasses and these sorts of glasses can be made of quite different kinds of materials than silica, metallic alloys, ionic melts, aqueous solutions, molecular liquids, and polymers. For many applications, like glass bottles or eyewear, polymer glasses are a lighter alternative than traditional glass, silica is a common fundamental constituent of glass. In nature, vitrification of quartz occurs when lightning strikes sand, forming hollow, fused quartz is a glass made from chemically-pure SiO2. It has excellent resistance to shock, being able to survive immersion in water while red hot. However, its high melting-temperature and viscosity make it difficult to work with, normally, other substances are added to simplify processing. One is sodium carbonate, which lowers the transition temperature. The soda makes the glass water-soluble, which is undesirable, so lime, some magnesium oxide. The resulting glass contains about 70 to 74% silica by weight and is called a soda-lime glass, soda-lime glasses account for about 90% of manufactured glass. Most common glass contains other ingredients to change its properties, lead glass or flint glass is more brilliant because the increased refractive index causes noticeably more specular reflection and increased optical dispersion. Adding barium also increases the refractive index, iron can be incorporated into glass to absorb infrared energy, for example in heat absorbing filters for movie projectors, while cerium oxide can be used for glass that absorbs UV wavelengths
6.
Asterism (gemology)
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Asterism, or star stone, is a name applied to the phenomenon of gemstones exhibiting a luminous star-like shape when cut en cabochon. The typical asteria is the sapphire, generally a bluish-grey corundum, milky or opalescent. In red corundum the stellate reflection is common, and hence the star-ruby occasionally found with the star-sapphire in Sri Lanka is among the most valued of fancy stones. Asterisms are also found in star-topaz, cymophane, the chatoyant chrysoberyl known as cats eye, may also be asteriated. In all these cases the asterism is due to the reflection of light from twin-lamellae or from extremely fine needle shaped acicular inclusions oriented to the crystal structure. Oriented sub-microscopic rutile crystals are a common inclusion in asterism gemstones, star-stones were formerly regarded with much superstition. An asterism is an optical phenomenon displayed by some rubies, sapphires, Star sapphires and rubies get their asterism from the titanium dioxide impurities present in them. The Star-effect or asterism is caused by the dense inclusions of tiny fibers of rutile, the stars are caused by the light reflecting from needle-like inclusions of rutile aligned perpendicular to the rays of the star. However, since rutile is always present in star gemstones, they are almost never completely transparent, diasterism, such as that seen in rose quartz, is the result of light transmitted through the stone. In order to see this effect, the stone must be illuminated from behind, isomorphism D. S. Phillips, T. E. Mitchell and A. H. Heuer, Precipitation in Star Sapphire I, Identification of the Precipitates, Phil
7.
Chatoyancy
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In gemology, chatoyancy, or chatoyance or cats eye effect, is an optical reflectance effect seen in certain gemstones. The precipitates that cause chatoyance in chrysoberyl are the mineral rutile, examined samples have yielded no evidence of tubes or fibres. The rutile precipitates all align perpendicularly with respect to cats eye effect and it is reasoned that the lattice parameter of the rutile matches only one of the three orthorhombic crystal axes of the chrysoberyl, resulting in preferred alignment along that direction. The effect can be likened to the sheen off a spool of silk, for a gemstone to show this effect best it must be cut en cabochon, with the fibers or fibrous structures parallel to the base of the finished gem. The best finished specimens show a sharply defined band of light that moves across the stone when it is rotated. Chatoyant stones of lesser quality display a banded effect as is typical with cats-eye varieties of quartz, faceted stones do not show the effect well. Glass optical cable can also display chatoyancy if properly cut, and has become a decorative material in a variety of vivid colors. The term cats eye, when used by itself as the name of a gemstone and it is also used as an adjective which indicates the chatoyance phenomenon in another stone, e. g. cats eye aquamarine. Figuring takes on a variety of forms and is referred to as flame, ribbon, tiger stripe and this effect is sometimes called wet look, since wetting wood with water often displays the chatoyancy, albeit only until the wood dries. Certain finishes cause the chatoyancy to become more pronounced, oil finishes, epoxy, and shellac can strongly bring out the wet look effect
8.
Diamond cut
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A diamond cut is a style or design guide used when shaping a diamond for polishing such as the brilliant cut. Cut does not refer to shape, but the symmetry, proportioning, the cut of a diamond greatly affects a diamonds brilliance, this means if it is cut poorly, it will be less luminous. In order to best use a diamond gemstones material properties, a number of different diamond cuts have been developed, a diamond cut constitutes a more or less symmetrical arrangement of facets, which together modify the shape and appearance of a diamond crystal. Diamond cutters must consider several factors, such as the shape and size of the crystal, the practical history of diamond cuts can be traced back to the Middle Ages, while their theoretical basis was not developed until the turn of the 20th century. The most popular of diamond cuts is the round brilliant, whose facet arrangements. Also popular are the cuts, which come in a variety of shapes—many of which were derived from the round brilliant. A diamonds cut is evaluated by trained graders, with higher grades given to stones whose symmetry, the strictest standards are applied to the round brilliant, although its facet count is invariable, its proportions are not. Different countries base their cut grading on different ideals, one may speak of the American Standard or the Scandinavian Standard, to give but two examples. The history of diamond cuts can be traced to the late Middle Ages and this was called the point cut and dates from the mid 14th century, by 1375 there was a guild of diamond polishers at Nürnberg. By the mid 15th century, the point cut began to be improved upon, the importance of a culet was also realised, and some table-cut stones may possess one. The addition of four corner facets created the old single cut, neither of these early cuts would reveal what diamond is prized for today, its strong dispersion or fire. At the time, diamond was valued chiefly for its lustre and superlative hardness. For this reason, colored gemstones such as ruby and sapphire were far more popular in jewelry of the era. In or around 1476, Lodewyk van Berquem, a Flemish polisher of Bruges, introduced the technique of absolute symmetry in the disposition of facets using a device of his own invention, the scaif. He cut stones in the known as pendeloque or briolette. However, Indian rose cuts were far less symmetrical as their cutters had the primary interest of conserving carat weight, in either event, the rose cut continued to evolve, with its depth, number and arrangements of facets being tweaked. The first brilliant cuts were introduced in the middle of the 17th century, known as Mazarins, they had 17 facets on the crown. They are also called double-cut brilliants as they are seen as a step up from old single cuts, yet Peruzzi-cut diamonds, when seen nowadays, seem exceedingly dull compared to modern-cut brilliants
9.
Diamond
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Diamond is a metastable allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the rate from diamond to graphite is negligible at standard conditions. Diamond is renowned as a material with superlative physical qualities, most of which originate from the covalent bonding between its atoms. In particular, diamond has the highest hardness and thermal conductivity of any bulk material and those properties determine the major industrial application of diamond in cutting and polishing tools and the scientific applications in diamond knives and diamond anvil cells. Because of its extremely rigid lattice, it can be contaminated by very few types of impurities, such as boron, small amounts of defects or impurities color diamond blue, yellow, brown, green, purple, pink, orange or red. Diamond also has relatively high optical dispersion, most natural diamonds are formed at high temperature and pressure at depths of 140 to 190 kilometers in the Earths mantle. Carbon-containing minerals provide the source, and the growth occurs over periods from 1 billion to 3.3 billion years. Diamonds are brought close to the Earths surface through deep volcanic eruptions by magma, Diamonds can also be produced synthetically in a HPHT method which approximately simulates the conditions in the Earths mantle. An alternative, and completely different growth technique is chemical vapor deposition, several non-diamond materials, which include cubic zirconia and silicon carbide and are often called diamond simulants, resemble diamond in appearance and many properties. Special gemological techniques have developed to distinguish natural diamonds, synthetic diamonds. The word is from the ancient Greek ἀδάμας – adámas unbreakable, the name diamond is derived from the ancient Greek αδάμας, proper, unalterable, unbreakable, untamed, from ἀ-, un- + δαμάω, I overpower, I tame. Diamonds have been known in India for at least 3,000 years, Diamonds have been treasured as gemstones since their use as religious icons in ancient India. Their usage in engraving tools also dates to early human history, later in 1797, the English chemist Smithson Tennant repeated and expanded that experiment. By demonstrating that burning diamond and graphite releases the same amount of gas, the most familiar uses of diamonds today are as gemstones used for adornment, a use which dates back into antiquity, and as industrial abrasives for cutting hard materials. The dispersion of light into spectral colors is the primary gemological characteristic of gem diamonds. In the 20th century, experts in gemology developed methods of grading diamonds, four characteristics, known informally as the four Cs, are now commonly used as the basic descriptors of diamonds, these are carat, cut, color, and clarity. A large, flawless diamond is known as a paragon and these conditions are met in two places on Earth, in the lithospheric mantle below relatively stable continental plates, and at the site of a meteorite strike. The conditions for diamond formation to happen in the mantle occur at considerable depth corresponding to the requirements of temperature and pressure
10.
Refractive index
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In optics, the refractive index or index of refraction n of a material is a dimensionless number that describes how light propagates through that medium. It is defined as n = c v, where c is the speed of light in vacuum, for example, the refractive index of water is 1.333, meaning that light travels 1.333 times faster in a vacuum than it does in water. The refractive index determines how light is bent, or refracted. The refractive indices also determine the amount of light that is reflected when reaching the interface, as well as the angle for total internal reflection. This implies that vacuum has a index of 1. The refractive index varies with the wavelength of light and this is called dispersion and causes the splitting of white light into its constituent colors in prisms and rainbows, and chromatic aberration in lenses. Light propagation in absorbing materials can be described using a refractive index. The imaginary part then handles the attenuation, while the real part accounts for refraction, the concept of refractive index is widely used within the full electromagnetic spectrum, from X-rays to radio waves. It can also be used with wave phenomena such as sound, in this case the speed of sound is used instead of that of light and a reference medium other than vacuum must be chosen. Thomas Young was presumably the person who first used, and invented, at the same time he changed this value of refractive power into a single number, instead of the traditional ratio of two numbers. The ratio had the disadvantage of different appearances, newton, who called it the proportion of the sines of incidence and refraction, wrote it as a ratio of two numbers, like 529 to 396. Hauksbee, who called it the ratio of refraction, wrote it as a ratio with a fixed numerator, hutton wrote it as a ratio with a fixed denominator, like 1.3358 to 1. Young did not use a symbol for the index of refraction, in the next years, others started using different symbols, n, m, and µ. For visible light most transparent media have refractive indices between 1 and 2, a few examples are given in the adjacent table. These values are measured at the yellow doublet D-line of sodium, with a wavelength of 589 nanometers, gases at atmospheric pressure have refractive indices close to 1 because of their low density. Almost all solids and liquids have refractive indices above 1.3, aerogel is a very low density solid that can be produced with refractive index in the range from 1.002 to 1.265. Moissanite lies at the end of the range with a refractive index as high as 2.65. Most plastics have refractive indices in the range from 1.3 to 1.7, for infrared light refractive indices can be considerably higher
11.
Cerussite
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Cerussite is a mineral consisting of lead carbonate, and an important ore of lead. The name is from the Latin cerussa, white lead, cerussa nativa was mentioned by Conrad Gessner in 1565, and in 1832 F. S. Beudant applied the name cruise to the mineral, whilst the present form, cerussite, is due to W. Haidinger. Miners names in use were lead-spar and white-lead-ore. Cerussite crystallizes in the system and is isomorphous with aragonite. Like aragonite it is very frequently twinned, the compound crystals being pseudo-hexagonal in form, three crystals are usually twinned together on two faces of the prism, producing six-rayed stellate groups with the individual crystals intercrossing at angles of nearly 60°. Crystals are of frequent occurrence and they usually have very bright, the mineral also occurs in compact granular masses, and sometimes in fibrous forms. The mineral is colorless or white, sometimes grey or greenish in tint. It is very brittle, and has a conchoidal fracture and it has a Mohs hardness of 3 to 3.75 and a specific gravity of 6.5. A variety containing 7% of zinc carbonate, replacing lead carbonate, is known as iglesiasite, from Iglesias in Sardinia, the mineral may be readily recognized by its characteristic twinning, in conjunction with the adamantine lustre and high specific gravity. It dissolves with effervescence in nitric acid. A blowpipe test will cause it to fuse very readily, delicate acicular crystals of considerable length were found long ago in the Pentire Glaze mine near St Minver in Cornwall. Cerussite is often found in quantities, and has a lead content of up to 77. 5%. Lead carbonate is insoluble in neutral water, but will dissolve in dilute acids. White lead is the key ingredient in lead paints, ingestion of lead-based paint chips is the most common cause of lead poisoning in children. Both white lead and lead acetate have been used in cosmetics throughout history, though this practice has ceased in Western countries
12.
Cubic zirconia
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Cubic zirconia is the cubic crystalline form of zirconium dioxide. The synthesized material is hard, optically flawless and usually colorless and it should not be confused with zircon, which is a zirconium silicate. It is sometimes erroneously called cubic zirconium and its main competitor as a synthetic gemstone is a more recently cultivated material, synthetic moissanite. Cubic zirconia is crystallographically isometric, an important attribute of a diamond simulant. During synthesis zirconium oxide would naturally form monoclinic crystals, its stable form under normal atmospheric conditions, therefore, the physical and optical properties of synthesized CZ vary, all values being ranges. It is a substance, with a specific gravity between 5.6 and 6.0 — at least 1.6 times that of diamond. Cubic zirconia is relatively hard, 8–8.5 on the Mohs scale— slightly harder than most semi-precious natural gems and its refractive index is high at 2. 15–2.18 and its luster is adamantine. Its dispersion is very high at 0. 058–0.066, Cubic zirconia has no cleavage and exhibits a conchoidal fracture. Because of its hardness, it is generally considered brittle. Under shortwave UV cubic zirconia typically fluoresces a yellow, greenish yellow or beige, under longwave UV the effect is greatly diminished, with a whitish glow sometimes being seen. Colored stones may show a strong, complex rare earth absorption spectrum, discovered in 1892, the yellowish monoclinic mineral baddeleyite is a natural form of zirconium oxide. The high melting point of zirconia hinders controlled growth of single crystals, however, stabilization of cubic zirconium oxide had been realized early on, with the synthetic product stabilized zirconia introduced in 1929. Although cubic, it was in the form of a ceramic, it was used as a refractory material. In 1937, German mineralogists M. V. Stackelberg and K. Chudoba discovered naturally occurring cubic zirconia in the form of microscopic grains included in metamict zircon. This was thought to be a byproduct of the metamictization process, the discovery was confirmed through X-ray diffraction, proving the existence of a natural counterpart to the synthetic product. Its production eventually exceeded that of earlier synthetics, such as strontium titanate, synthetic rutile, YAG. Some of the earliest research into controlled single-crystal growth of cubic zirconia occurred in 1960s France, though promising, these attempts yielded only small crystals. Later, Soviet scientists under V. V. Osiko at the Lebedev Physical Institute in Moscow perfected the technique and they named the jewel Fianit after the institutes name FIAN, but the name was not used outside of the USSR
13.
Garnet
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Garnets are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. All species of garnets possess similar physical properties and crystal forms, the different species are pyrope, almandine, spessartine, grossular, uvarovite and andradite. The garnets make up two solid solution series, pyrope-almandine-spessartine and uvarovite-grossular-andradite, the word garnet comes from the 14th‑century Middle English word gernet, meaning dark red. It is derived from the Latin granatus, from granum, Garnet species are found in many colors including red, orange, yellow, green, purple, brown, blue, black, pink, and colorless, with reddish shades most common. Garnet species light transmission properties can range from the gemstone-quality transparent specimens to the varieties used for industrial purposes as abrasives. The minerals luster is categorized as vitreous or resinous, garnets are nesosilicates having the general formula X3Y23. The X site is occupied by divalent cations 2+ and the Y site by trivalent cations 3+ in an octahedral/tetrahedral framework with 4− occupying the tetrahedra. Garnets are most often found in the crystal habit, but are also commonly found in the trapezohedron habit. They crystallize in the system, having three axes that are all of equal length and perpendicular to each other. Garnets do not show cleavage, so when they fracture under stress, because the chemical composition of garnet varies, the atomic bonds in some species are stronger than in others. As a result, this group shows a range of hardness on the Mohs scale of about 6.5 to 7.5. The harder species like almandine are often used for abrasive purposes, for gem identification purposes, a pick-up response to a strong neodymium magnet separates garnet from all other natural transparent gemstones commonly used in the jewelry trade. Almandine, Fe3Al23 Pyrope, Mg3Al23 Spessartine, Mn3Al23 Almandine, sometimes incorrectly called almandite, is the modern gem known as carbuncle, the term carbuncle is derived from the Latin meaning live coal or burning charcoal. The name Almandine is a corruption of Alabanda, a region in Asia Minor where these stones were cut in ancient times, chemically, almandine is an iron-aluminium garnet with the formula Fe3Al23, the deep red transparent stones are often called precious garnet and are used as gemstones. Almandine occurs in metamorphic rocks like mica schists, associated with such as staurolite, kyanite, andalusite. Almandine has nicknames of Oriental garnet, almandine ruby, and carbuncle, Pyrope is red in color and chemically an aluminium silicate with the formula Mg3Al23, though the magnesium can be replaced in part by calcium and ferrous iron. The color of pyrope varies from red to black. A variety of pyrope from Macon County, North Carolina is a shade and has been called rhodolite
14.
Corundum
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Corundum is a crystalline form of aluminium oxide typically containing traces of iron, titanium, vanadium and chromium. It is a transparent material, but can have different colors when impurities are present. Transparent specimens are used as gems, called ruby if red, all other colors are called sapphire, e. g. green sapphire for a green specimen. The name corundum is derived from the Tamil word Kurundam which originates from the Sanskrit word Kuruvinda meaning ruby, because of corundums hardness, it can scratch almost every other mineral. It is commonly used as an abrasive on everything from sandpaper to large machines used in machining metals, plastics, some emery is a mix of corundum and other substances, and the mix is less abrasive, with an average Mohs hardness of 8.0. In addition to its hardness, corundum is unusual for its density of 4.02 g/cm3, corundum occurs as a mineral in mica schist, gneiss, and some marbles in metamorphic terranes. It also occurs in low silica igneous syenite and nepheline syenite intrusives, other occurrences are as masses adjacent to ultramafic intrusives, associated with lamprophyre dikes and as large crystals in pegmatites. It commonly occurs as a mineral in stream and beach sands because of its hardness. The largest documented crystal of corundum measured about 65×40×40 cm. The record has since surpassed by certain synthetic boules. Corundum for abrasives is mined in Zimbabwe, Russia, Sri Lanka, historically it was mined from deposits associated with dunites in North Carolina, US and from a nepheline syenite in Craigmont, Ontario. Emery-grade corundum is found on the Greek island of Naxos and near Peekskill, New York, abrasive corundum is synthetically manufactured from bauxite. Four corundum axes dating back to 2500 BCE from the Liangzhou culture have been discovered in China, in 1837, Marc Antoine Gaudin made the first synthetic rubies by fusing alumina at a high temperature with a small amount of chromium as a pigment. In 1847, Ebelmen made white synthetic sapphires by fusing alumina in boric acid, in 1877 Frenic and Freil made crystal corundum from which small stones could be cut. Frimy and Auguste Verneuil manufactured artificial ruby by fusing BaF2, in 1903, Verneuil announced he could produce synthetic rubies on a commercial scale using this flame fusion process. The Verneuil process allows the production of flawless single-crystal sapphires, rubies and it is also possible to grow gem-quality synthetic corundum by flux-growth and hydrothermal synthesis. Corundum crystallizes with trigonal symmetry in the space group R3c and has the lattice parameters a =4.75 Å and c =12.982 Å at standard conditions, the unit cell contains six formula units. In the lattice of corundum, the atoms form a slightly distorted hexagonal close packing
15.
Kaolinite
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Kaolinite /ˈkeɪəlᵻˌnaɪt/ is a clay mineral, part of the group of industrial minerals, with the chemical composition Al2Si2O54. It is a silicate mineral, with one tetrahedral sheet of silica linked through oxygen atoms to one octahedral sheet of alumina octahedra. Rocks that are rich in kaolinite are known as kaolin /ˈkeɪəlᵻn/ or china clay, the name kaolin is derived from Gaoling, a Chinese village near Jingdezhen in southeastern Chinas Jiangxi Province. The name entered English in 1727 from the French version of the word, kaolin, kaolinite has a low shrink–swell capacity and a low cation-exchange capacity. It is a soft, earthy, usually white, mineral, in many parts of the world it is colored pink-orange-red by iron oxide, giving it a distinct rust hue. Lighter concentrations yield white, yellow, or light orange colors, alternating layers are sometimes found, as at Providence Canyon State Park in Georgia, United States. Commercial grades of kaolin are supplied and transported as dry powder, kaolinite group clays undergo a series of phase transformations upon thermal treatment in air at atmospheric pressure. Below 100 °C, exposure to dry air will slowly remove liquid water from the kaolin, the end-state for this transformation is referred to as leather dry. Between 100 °C and about 550 °C, any remaining water is expelled from kaolinite. The end state for this transformation is referred to as bone dry, throughout this temperature range, the expulsion of water is reversible, if the kaolin is exposed to liquid water, it will be reabsorbed and disintegrate into its fine particulate form. Subsequent transformations are not reversible, and represent permanent chemical changes, endothermic dehydration of kaolinite begins at 550–600 °C producing disordered metakaolin, but continuous hydroxyl loss is observed up to 900 °C. Al2Si2O54 → Al2Si2O7 +2 H2O, further heating to 925–950 °C converts metakaolin to an aluminium-silicon spinel which is sometimes also referred to as a gamma-alumina type structure,2 Al2Si2O7 → Si3Al4O12 + SiO2. Upon calcination above 1050 °C, the spinel phase nucleates and transforms to platelet mullite, finally, at 1400 °C the needle form of mullite appears, offering substantial increases in structural strength and heat resistance. This is a structural but not chemical transformation, see stoneware for more information on this form. Kaolinite clay occurs in abundance in soils that have formed from the weathering of rocks in hot. Such climatically-related differences in mineral content are often used to infer changes in climates in the geological past. In the Institut National pour lEtude Agronomique au Congo Belge classification system, in the US the main kaolin deposits are found in central Georgia, on a stretch of the Atlantic Seaboard fall line between Augusta and Macon. The deposits were formed between the late Cretaceous and early Paleogene, about 100 million to 45 million years ago, in sediments derived from weathered igneous, Kaolin production in the US during 2011 was 5.5 million tonnes
16.
Opal
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Opal is a hydrated amorphous form of silica, its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Because of its amorphous character, it is classed as a mineraloid, unlike crystalline forms of silica, which are classed as minerals. It is deposited at a low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, marl. Opal is the gemstone of Australia. The internal structure of precious opal makes it diffract light, depending on the conditions in which it formed, it can take on many colors. Precious opal ranges from clear white, gray, red, orange, yellow, green, blue, magenta, rose, pink, slate, olive, brown. Of these hues, the black opals are the most rare, whereas white, opals vary in optical density from opaque to semitransparent. Precious opal shows a variable interplay of colors, and though it is a mineraloid. At microscopic scales, precious opal is composed of silica spheres some 150 to 300 nm in diameter in a hexagonal or cubic close-packed lattice, the regularity of the sizes and the packing of these spheres determines the quality of precious opal. The colors that are observed are determined by the spacing between the planes and the orientation of planes with respect to the incident light, the process can be described by Braggs law of diffraction. Visible light of diffracted wavelengths cannot pass through large thicknesses of the opal and this is the basis of the optical band gap in a photonic crystal. The notion that opals are photonic crystals for visible light was expressed in 1995 by Vasily Astratovs group, in addition, microfractures may be filled with secondary silica and form thin lamellae inside the opal during solidification. The term opalescence is commonly and erroneously used to describe this unique and beautiful phenomenon, contrarily, opalescence is correctly applied to the milky, turbid appearance of common or potch opal. Potch does not show a play of color, for gemstone use, most opal is cut and polished to form a cabochon. Solid opal refers to polished stones consisting wholly of precious opal, opals too thin to produce a solid may be combined with other materials to form attractive gems. An opal doublet consists of a thin layer of precious opal, backed by a layer of dark-colored material, most commonly ironstone, dark or black common opal, onyx. The darker backing emphasizes the play of color, and results in an attractive display than a lighter potch. An opal triplet is similar to a doublet, but has a third layer, the cap takes a high polish and acts as a protective layer for the opal
17.
Cordierite
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For the green variety of quartz see prasiolite. Cordierite or iolite is an iron aluminium cyclosilicate. Iron is almost always present and a solution exists between Mg-rich cordierite and Fe-rich sekaninaite with a series formula, 2Al3 to 2Al3. A high-temperature polymorph exists, indialite, which is isostructural with beryl and has a distribution of Al in the 6O18 rings. Cordierite, which was discovered in 1813, is named after the French geologist Louis Cordier, cordierite typically occurs in contact or regional metamorphism of pelitic rocks. It is especially common in hornfels produced by metamorphism of pelitic rocks. Two common metamorphic mineral assemblages include sillimanite-cordierite-spinel and cordierite-spinel-plagioclase-orthopyroxene, other associated minerals include garnet and anthophyllite. Cordierite also occurs in some granites, pegmatites, and norites in gabbroic magmas, alteration products include mica, chlorite, and talc. Cordierite occurs, for example, in the contact zone at Geevor Tin Mine in Cornwall. Catalytic converters are made from ceramics containing a large proportion of synthetic cordierite. The manufacturing process aligns the cordierite crystals to make use of the very low thermal expansion along one axis. This prevents thermal shock cracking from taking place when the catalytic converter is used, as the transparent variety iolite, it is often used as a gemstone. The name iolite comes from the Greek word for violet, another old name is dichroite, a Greek word meaning two-colored rock, a reference to cordierites strong pleochroism. It has also been called water-sapphire and Vikings Compass because of its usefulness in determining the direction of the sun on overcast days and this works by determining the direction of polarization of the sky overhead. Gem quality iolite varies in color from blue to blue violet to yellowish gray to light blue as the light angle changes. Iolite is sometimes used as a substitute for sapphire. It is much softer than sapphires and is found in Australia, Brazil, Burma, Canada, India, Madagascar, Namibia, Sri Lanka, Tanzania. The largest iolite crystal found weighed more than 24,000 carats, another name for blue iolite is steinheilite, after Fabian Steinheil, the Russian military governor of Finland who observed that it was a different mineral from quartz
18.
Pyrite
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The mineral pyrite, or iron pyrite, also known as fools gold, is an iron sulfide with the chemical formula FeS2. This minerals metallic luster and pale brass-yellow hue give it a resemblance to gold. The color has led to the nicknames brass, brazzle. Pyrite is the most common of the sulfide minerals, the name pyrite is derived from the Greek πυρίτης, of fire or in fire, in turn from πύρ, fire. 1550, the term had become a term for all of the sulfide minerals. Pyrite is usually associated with other sulfides or oxides in quartz veins, sedimentary rock. Despite being nicknamed fools gold, pyrite is sometimes found in association with small quantities of gold, Gold and arsenic occur as a coupled substitution in the pyrite structure. In the Carlin–type gold deposits, arsenian pyrite contains up to 0.37 wt% gold, Pyrite has been used since classical times to manufacture copperas, that is, iron sulfate. Iron pyrite was heaped up and allowed to weather, the acidic runoff from the heap was then boiled with iron to produce iron sulfate. In the 15th century, such leaching began to replace the burning of sulfur as a source of sulfuric acid, by the 19th century, it had become the dominant method. Pyrite remains in use for the production of sulfur dioxide, for use in such applications as the paper industry. Thermal decomposition of pyrite into FeS and elemental sulfur starts at 540 °C, a newer commercial use for pyrite is as the cathode material in Energizer brand non-rechargeable lithium batteries. Pyrite is a material with a band gap of 0.95 eV. During the early years of the 20th century, pyrite was used as a detector in radio receivers. Pyrite detectors occupied a midway point between galena detectors and the more mechanically complicated perikon mineral pairs, Pyrite detectors can be as sensitive as a modern 1N34A germanium diode detector. Pyrite has been proposed as an abundant, inexpensive material in low-cost photovoltaic solar panels, synthetic iron sulfide was used with copper sulfide to create the photovoltaic material. Pyrite is used to make marcasite jewelry, marcasite jewelry, made from small faceted pieces of pyrite, often set in silver, was known since ancient times and was popular in the Victorian era. Marcasite jewelry does not actually contain the mineral marcasite, from the perspective of classical inorganic chemistry, which assigns formal oxidation states to each atom, pyrite is probably best described as Fe2+S22−
19.
Ideal surface
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An ideal solid surface is flat, rigid, perfectly smooth, and chemically homogeneous, and has zero contact angle hysteresis. Zero hysteresis implies the advancing and receding contact angles are equal, in other words, only one thermodynamically stable contact angle exists. When a drop of liquid is placed on such a surface, furthermore, on an ideal surface, the drop will return to its original shape if it is disturbed. The following derivations apply only to solid surfaces, they are only valid for the state in which the interfaces are not moving. Figure 3 shows the line of contact where three phases meet, in equilibrium, the net force per unit length acting along the boundary line between the three phases must be zero. These relations can also be expressed by an analog to a known as Neumann’s triangle. If three fluids with surface energies that do not follow these inequalities are brought into contact, no equilibrium configuration consistent with Figure 3 will exist, subsequently, this predicts the contact angle of a liquid droplet on a solid surface from knowledge of the three surface energies involved. This equation also applies if the gas phase is another liquid, the Young equation assumes a perfectly flat and rigid surface. In many cases, surfaces are far from this ideal situation, even in a perfectly smooth surface, a drop will assume a wide spectrum of contact angles ranging from the so-called advancing contact angle, θ A, to the so-called receding contact angle, θ R. The consequence of this restriction is the prediction of complete wetting when γSG > γSL + γLG, the lack of a solution to the Young–Dupré equation is an indicator that there is no equilibrium configuration with a contact angle between 0 and 180° for those situations. A useful parameter for gauging wetting is the spreading parameter S, S = γ S G − When S >0, when S <0, partial wetting occurs. Combining the spreading parameter definition with the Young relation yields the Young–Dupré equation, contact angle hysteresis Wetting Surface roughness
20.
Reflection (physics)
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Reflection is the change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves, the law of reflection says that for specular reflection the angle at which the wave is incident on the surface equals the angle at which it is reflected. In acoustics, reflection causes echoes and is used in sonar, in geology, it is important in the study of seismic waves. Reflection is observed with surface waves in bodies of water, Reflection is observed with many types of electromagnetic wave, besides visible light. Reflection of VHF and higher frequencies is important for radio transmission, even hard X-rays and gamma rays can be reflected at shallow angles with special grazing mirrors. Reflection of light is either specular or diffuse depending on the nature of the interface, a mirror provides the most common model for specular light reflection, and typically consists of a glass sheet with a metallic coating where the reflection actually occurs. Reflection is enhanced in metals by suppression of wave propagation beyond their skin depths, Reflection also occurs at the surface of transparent media, such as water or glass. In the diagram, a light ray PO strikes a vertical mirror at point O, by projecting an imaginary line through point O perpendicular to the mirror, known as the normal, we can measure the angle of incidence, θi and the angle of reflection, θr. The law of reflection states that θi = θr, or in other words, in fact, reflection of light may occur whenever light travels from a medium of a given refractive index into a medium with a different refractive index. In the most general case, a fraction of the light is reflected from the interface. This is analogous to the way impedance mismatch in a circuit causes reflection of signals. Total internal reflection of light from a denser medium occurs if the angle of incidence is above the critical angle, total internal reflection is used as a means of focusing waves that cannot effectively be reflected by common means. X-ray telescopes are constructed by creating a tunnel for the waves. As the waves interact at low angle with the surface of this tunnel they are reflected toward the focus point, a conventional reflector would be useless as the X-rays would simply pass through the intended reflector. When light reflects off a material denser than the external medium, in contrast, a less dense, lower refractive index material will reflect light in phase. This is an important principle in the field of thin-film optics, specular reflection at a curved surface forms an image which may be magnified or demagnified, curved mirrors have optical power. Such mirrors may have surfaces that are spherical or parabolic, if the reflecting surface is very smooth, the reflection of light that occurs is called specular or regular reflection. The laws of reflection are as follows, The incident ray, the reflected ray, the angle which the incident ray makes with the normal is equal to the angle which the reflected ray makes to the same normal
21.
Galena
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Galena, also called lead glance, is the natural mineral form of lead sulfide. It is the most important ore of lead and an important source of silver, Galena is one of the most abundant and widely distributed sulfide minerals. It crystallizes in the crystal system often showing octahedral forms. It is often associated with the minerals sphalerite, calcite and fluorite, Galena is the main ore of lead, used since ancient times. Because of its low melting point, it was easy to liberate by smelting. In some deposits galena contains about 1–2% silver, a byproduct that far outweighs the main ore in revenue. Galena deposits often contain significant amounts of silver as included silver sulfide mineral phases or as limited solid solution within the galena structure. These argentiferous galenas have long been the most important ore of silver, Galena deposits are found worldwide in various environments. Galena also occurs in North African countries and at Mount Hermon in Northern Israel, in the United States, it occurs most notably in the Mississippi Valley type deposits of the Lead Belt in southeastern Missouri, and in the Driftless Area of Illinois, Iowa and Wisconsin. The economic importance of galena to the history of the Driftless Area was so great that one of the towns in the region was named Galena. Galena also was a mineral of the zinc-lead mines of the tri-state district around Joplin in southwestern Missouri. Galena is also an important ore mineral in the mining regions of Colorado, Idaho, Utah. Of the latter, the Coeur dAlene district of northern Idaho was most prominent, Galena is the official state mineral of the U. S. states of Missouri and Wisconsin, the former mining town of Galena, Kansas takes its name from deposits of this mineral. Derbyshire in the UK was one of the areas where galena was mined. The largest documented crystal of galena is composite cubo-octahedra from the Great Laxey Mine, Isle of Man, Galena belongs to the octahedral sulfide group of minerals that have metal ions in octahedral positions, such as the iron sulfide pyrrhotite and the nickel arsenide niccolite. The galena group is named after its most common member, with other members that include manganese bearing alabandite and niningerite. Divalent lead cations and sulfur anions form a cubic unit cell much like the mineral halite of the halide mineral group. Zinc, cadmium, iron, copper, antimony, arsenic, bismuth, selenium substitutes for sulfur in the structure constituting a solid solution series
22.
Magnetite
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Magnetite is a mineral and one of the main iron ores. With the chemical formula Fe3O4, it is one of the oxides of iron, Magnetite is ferrimagnetic, it is attracted to a magnet and can be magnetized to become a permanent magnet itself. It is the most magnetic of all the minerals on Earth. Naturally-magnetized pieces of magnetite, called lodestone, will attract small pieces of iron, today it is mined as iron ore. Small grains of magnetite occur in almost all igneous and metamorphic rocks, Magnetite is black or brownish-black with a metallic luster, has a Mohs hardness of 5–6 and leaves a black streak. The chemical IUPAC name is iron oxide and the chemical name is ferrous-ferric oxide. In addition to rocks, magnetite also occurs in sedimentary rocks, including banded iron formations and in lake. Magnetite nanoparticles are also thought to form in soils, where they probably oxidize rapidly to maghemite, Magnetite has an inverse spinel crystal structure. As a member of the group, it can form solid solutions with similarly structured minerals, including ulvospinel. Titanomagnetite, also known as titaniferous magnetite, is a solution between magnetite and ulvospinel that crystallizes in many mafic igneous rocks. Titanomagnetite may undergo oxyexsolution during cooling, resulting in ingrowths of magnetite and ilmenite, Magnetite has been important in understanding the conditions under which rocks form. Magnetite reacts with oxygen to produce hematite, and the pair forms a buffer that can control oxygen fugacity. Commonly, igneous rocks contain solid solutions of both titanomagnetite and hemoilmenite or titanohematite, Magnetite also is produced from peridotites and dunites by serpentinization. Lodestones were used as a form of magnetic compass. At low temperatures, magnetite undergoes a crystal structure phase transition from a structure to a cubic structure known as the Verwey transition. The Verwey transition occurs around 121 K and is dependent on size, domain state. An isotropic point also occurs near the Verwey transition around 130 K, the Curie temperature of magnetite is 858 K. Magnetite is sometimes found in large quantities in beach sand. Such black sands are found in places, such as Lung Kwu Tan of Hong Kong, California of the United States
23.
Muscovite
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Muscovite is a hydrated phyllosilicate mineral of aluminium and potassium with formula KAl22, or 236. It has a perfect basal cleavage yielding remarkably thin laminae which are often highly elastic. Sheets of muscovite 5 m ×3 m have been found in Nellore, Muscovite has a Mohs hardness of 2–2.25 parallel to the face,4 perpendicular to the and a specific gravity of 2. 76–3. It can be colorless or tinted through grays, browns, greens, yellows, or violet or red and it is anisotropic and has high birefringence. The green, chromium-rich variety is called fuchsite, mariposite is also a type of muscovite. In pegmatites, it is found in immense sheets that are commercially valuable. Muscovite is in demand for the manufacture of fireproofing and insulating materials, the name muscovite comes from Muscovy-glass, a name given to the mineral in Elizabethan England due to its use in medieval Russia as a cheaper alternative to glass in windows. Media related to Muscovite at Wikimedia Commons
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Pearl
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A pearl is a hard object produced within the soft tissue of a living shelled mollusk or another animal, such as a conulariid. Just like the shell of a clam, a pearl is composed of calcium carbonate. in minute crystalline form, the ideal pearl is perfectly round and smooth, but many other shapes, known as baroque pearls, can occur. The finest quality natural pearls have been valued as gemstones. Because of this, pearl has become a metaphor for something rare, fine, the most valuable pearls occur spontaneously in the wild, but are extremely rare. These wild pearls are referred to as natural pearls, cultured or farmed pearls from pearl oysters and freshwater mussels make up the majority of those currently sold. Imitation pearls are widely sold in inexpensive jewelry, but the quality of their iridescence is usually very poor and is easily distinguished from that of genuine pearls. Pearls have been harvested and cultivated primarily for use in jewelry and they have also been crushed and used in cosmetics, medicines and paint formulations. Whether wild or cultured, gem-quality pearls are almost always nacreous and iridescent, however, almost all species of shelled mollusks are capable of producing pearls of lesser shine or less spherical shape. The English word pearl comes from the French perle, originally from the Latin perna meaning leg, nacreous pearls, the best-known and most commercially significant, are primarily produced by two groups of molluskan bivalves or clams. A nacreous pearl is made from layers of nacre, by the same living process as is used in the secretion of the mother of pearl which lines the shell, natural pearls, formed without human intervention, are very rare. Cultured pearls are formed in pearl farms, using human intervention as well as natural processes, saltwater pearls can grow in several species of marine pearl oysters in the family Pteriidae. Freshwater pearls grow within certain species of mussels in the order Unionida. The unique luster of pearls depends upon the reflection, refraction, the thinner and more numerous the layers in the pearl, the finer the luster. The iridescence that pearls display is caused by the overlapping of successive layers, in addition, pearls can be dyed yellow, green, blue, brown, pink, purple, or black. The very best pearls have a metallic mirror-like luster, because pearls are made primarily of calcium carbonate, they can be dissolved in vinegar. Calcium carbonate is susceptible to even a weak acid solution because the crystals of calcium carbonate react with the acid in the vinegar to form calcium acetate. Freshwater and saltwater pearls may sometimes look quite similar, but they come from different sources, Freshwater pearls form in various species of freshwater mussels, family Unionidae, which live in lakes, rivers, ponds and other bodies of fresh water. These freshwater pearl mussels occur not only in hotter climates, most freshwater cultured pearls sold today come from China
25.
Cleavage (crystal)
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Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite crystallographic structural planes. Cleavage forms parallel to planes, Basal or pinacoidal cleavage occurs when there is only one cleavage plane. Mica also has basal cleavage, this is why mica can be peeled into thin sheets, cubic cleavage occurs on when there are three cleavage planes intersecting at 90 degrees. Halite has cubic cleavage, and therefore, when halite crystals are broken, octahedral cleavage occurs when there are four cleavage planes in a crystal. Octahedral cleavage is common for semiconductors, rhombohedral cleavage occurs when there are three cleavage planes intersecting at angles that are not 90 degrees. Prismatic cleavage occurs when there are two planes in a crystal. Dodecahedral cleavage occurs when there are six cleavage planes in a crystal, crystal parting occurs when minerals break along planes of structural weakness due to external stress or along twin composition planes. Parting breaks are very similar in appearance to cleavage, but only due to stress. Examples include magnetite which shows octahedral parting, the parting of corundum. Cleavage is a property traditionally used in mineral identification, both in hand specimen and microscopic examination of rock and mineral studies. As an example, the angles between the cleavage planes for the pyroxenes and the amphiboles are diagnostic. Crystal cleavage is of importance in the electronics industry and in the cutting of gemstones. Precious stones are generally cleaved by impact, as in diamond cutting, synthetic single crystals of semiconductor materials are generally sold as thin wafers which are much easier to cleave. Elemental semiconductors are diamond cubic, a group for which octahedral cleavage is observed. This means that some orientations of wafer allow near-perfect rectangles to be cleaved, most other commercial semiconductors can be made in the related zinc blende structure, with similar cleavage planes. Cleavage Mineral galleries, Mineral properties – Cleavage
26.
Stilbite
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Stilbite is the name of a series of tectosilicate minerals of the zeolite group. In the case of stilbite-Na, sodium dominates over calcium, the species are visually indistinguishable, and the series name stilbite is still used whenever testing has not been performed. At one time heulandite and stilbite were considered to be identical minerals, after they were found to be two separate species, in 1818, the name desmine was proposed for stilbite, and this name is still employed in Germany. The English name stilbite is from the Greek stilbein = to shine, stilbite shows a wide variation in exchangeable cations, silicon and aluminium ions occupy equivalent sites and can substitute for each other. Since silicon and aluminium have a different charge the ions occupying the site have to adjust to maintain charge balance. There is a series between stellerite, whose formula can be written as Ca4O72·28, and stilbite, and another continuous series between stilbite and barrerite, Na8O72·26. Epistilbite is a distinct zeolite species unrelated to stilbite, stilbite is usually monoclinic 2/m, meaning that it has one twofold axis of rotational symmetry perpendicular to a mirror plane. The twofold axis is the crystal axis b, and the a and c axes lie in the mirror plane. For a monoclinic crystal a and c are inclined to each other at an angle β which is not a right angle, for stilbite β is nearly 130°. The mineral is said to be pseudo-orthorhombic, non-endmember forms of stilbite may be triclinic or even truly orthorhombic, indeed the framework can have symmetry ranging from orthorhombic to triclinic in a single crystal. Crystals are typically tabular, flattened parallel to the dominant cleavage. Aggregates may be sheaf-like or in bow-ties, also fibrous and globular, twinning, cruciform and penetration, is extremely common on. The color is colorless or white, also yellow, brown, pink, salmon, orange, red, green. The luster is vitreous, and on the perfect cleavage parallel to the plane of symmetry it is markedly pearly. The streak is white and crystals are transparent to translucent, the hardness is 3½ to 4 and the specific gravity 2.12 to 2.22. Cleavage is perfect on, poor on, the mineral is brittle, with a conchoidal or uneven fracture. The unit cell can be considered as a cell with β close to 130° and one formula unit per unit cell, or as a larger pseudo-orthorhombic cell with β close to 90°. It has 10-member rings and 8-member rings forming channels parallel to a, the open channels in the stilbite structure act like a molecular sieve, enabling it to separate hydrocarbons in the process of petroleum refining
27.
Amber
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Amber is fossilized tree resin, which has been appreciated for its color and natural beauty since Neolithic times. Much valued from antiquity to the present as a gemstone, amber is made into a variety of decorative objects and it has also been used as a healing agent in folk medicine. There are five classes of amber, defined on the basis of their chemical constituents, because it originates as a soft, sticky tree resin, amber sometimes contains animal and plant material as inclusions. Amber occurring in coal seams is also called resinite, and the term ambrite is applied to that found specifically within New Zealand coal seams, the English word amber derives from Arabic ʿanbar عنبر via Middle Latin ambar and Middle French ambre. The word was adopted in Middle English in the 14th century as referring to what is now known as ambergris, in the Romance languages, the sense of the word had come to be extended to Baltic amber from as early as the late 13th century. At first called white or yellow amber, this meaning was adopted in English by the early 15th century, as the use of ambergris waned, this became the main sense of the word. The two substances conceivably became associated or confused because they both were washed up on beaches. Ambergris is less dense water and floats, whereas amber is too dense to float. The classical names for amber, Latin electrum and Ancient Greek ἤλεκτρον, are connected to a term ἠλέκτωρ meaning beaming Sun, according to myth, when Phaëton son of Helios was killed, his mourning sisters became poplar trees, and their tears became elektron, amber. Earlier Pliny says that an island of three days sail from the Scythian coast called Balcia by Xenophon of Lampsacus, author of a fanciful travel book in Greek, is called Basilia by Pytheas. It is generally understood to be the same as Abalus and it is assumed that there were well-established trade routes for amber connecting the Baltic with the Mediterranean. Pliny states explicitly that the Germans export amber to Pannonia, from where it was traded further abroad by the Veneti, the ancient Italic peoples of southern Italy were working amber, the most important examples are on display at the National Archaeological Museum of Siritide to Matera. Amber used in antiquity as at Mycenae and in the prehistory of the Mediterranean comes from deposits of Sicily. Besides the fanciful explanations according to which amber is produced by the Sun, Pliny cites opinions that are aware of its origin in tree resin. Amber is produced from a marrow discharged by trees belonging to the genus, like gum from the cherry. This is confirmed by the recorded Old High German glas and Old English glær for amber, in Middle Low German, amber was known as berne-, barn-, börnstēn. The Low German term became dominant also in High German by the 18th century, the Baltic Lithuanian term for amber is gintaras and Latvian dzintars. They, and the Slavic jantar or Hungarian gyanta, are thought to originate from Phoenician jainitar, Early in the nineteenth century, the first reports of amber from North America came from discoveries in New Jersey along Crosswicks Creek near Trenton, at Camden, and near Woodbury
28.
Resin
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In polymer chemistry and materials science, resin is a solid or highly viscous substance of plant or synthetic origin that is typically convertible into polymers. They are often mixtures of compounds, principally terpenes. Many plants, particularly woody plants, produce resin in response to injury, the resin acts as a bandage protecting the plant from invading insects and pathogens. Plants secrete resins and rosins for their protective benefits, the resin produced by most plants is composed mainly of terpenes and derivatives. Some resins also contain a proportion of resin acids. The individual components of resin can be separated by fractional distillation, rosins on the other hand are less volatile and consist, inter alia, of diterpenes. Amber is fossil resin from coniferous and other tree species, copal, kauri gum, dammar and other resins may also be found as subfossil deposits. Subfossil copal can be distinguished from genuine fossil amber because it becomes tacky when a drop of a solvent such as acetone or chloroform is placed on it, african copal and the kauri gum of New Zealand are also procured in a semi-fossil condition. Solidified resin from which the volatile terpene components have been removed by distillation is known as rosin, typical rosin is a transparent or translucent mass, with a vitreous fracture and a faintly yellow or brown colour, non-odorous or having only a slight turpentine odor and taste. Rosin is insoluble in water, mostly soluble in alcohol, essential oils, ether and hot fatty oils, and softens and melts under the influence of heat, rosin consists of a complex mixture of different substances including organic acids named the resin acids. These are closely related to the terpenes, and derive from them through partial oxidation, Resin acids can be dissolved in alkalis to form resin soaps, from which the purified resin acids are regenerated by treatment with acids. Examples of resin acids are abietic acid, C20H30O2, plicatic acid contained in cedar, and pimaric acid, C20H30O2, a constituent of galipot resin. Abietic acid can also be extracted from rosin by means of hot alcohol, it crystallizes in leaflets, pimaric acid closely resembles abietic acid into which it passes when distilled in a vacuum, it has been supposed to consist of three isomers. Rosin is obtained from pines and some plants, mostly conifers. Propolis, consisting largely of resins collected from such as poplars and conifers, is used by honey bees to seal gaps in their hives. Shellac and lacquer are examples of insect-derived resins, asphaltite and Utah resin are petroleum bitumens, not a product secreted by plants, although it was ultimately derived from plants. These were highly prized substances, and required as incense in religious rites. The word resin has been applied in the world to nearly any component of a liquid that will set into a hard lacquer or enamel-like finish
29.
Chewing gum
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Chewing gum is a soft, cohesive substance designed to be chewed without being swallowed. Modern chewing gum is composed of gum base, sweeteners, softeners/ plasticizers, flavors, colors, and, typically, a hard or powdered polyol coating. The cultural tradition of chewing gum seems to have developed through a convergent evolution process, each of the early precursors to chewing gum were derived from natural growths local to the region and were chewed purely out the instinctual desire to masticate. Early chewers did not necessarily desire to derive benefits from their chewable substances. Chewing gum in many forms has existed since the Neolithic period,6, 000-year-old chewing gum made from birch bark tar, with tooth imprints, has been found in Kierikki in Finland. The tar from which the gums were made is believed to have antiseptic properties and it is chemically similar to petroleum tar and is in this way different from most other early gum. The Aztecs, as the ancient Mayans before them, used chicle, forms of chewing gums were also chewed in Ancient Greece. The Ancient Greeks chewed mastic gum, made from the resin of the mastic tree, mastic gum, like birch bark tar, has antiseptic properties and is believed to have been used to maintain oral health. Both chicle and mastic are tree resins, many other cultures have chewed gum-like substances made from plants, grasses, and resins. Although chewing gum can be traced back to civilizations around the world, the American Indians chewed resin made from the sap of spruce trees. The New England settlers picked up this practice, and in 1848, John B. Curtis developed, in this way, the industrializing West, having forgotten about tree gums, rediscovered chewing gum through the First Americans. Around 1850 a gum made from wax, which is a petroleum product, was developed. To sweeten these early gums the chewer would often use of a plate of powdered sugar. William Semple filed a patent on chewing gum, patent number 98,304. The first flavored chewing gum was created in the 1860s by John Colgan, Colgan mixed with powdered sugar the aromatic flavoring tolu, a powder obtained from an extract of the balsam tree, creating small sticks of flavored chewing gum he named Taffy Tolu. Colgan also lead the way in the manufacturing and packaging of chicle-based chewing gum, derived from Manilkara chicle, chicle did not succeed as a replacement for rubber, but as a gum, which was cut into strips and marketed as Adams New York Chewing Gum in 1871. Black Jack, which is flavored with licorice, Chiclets, Chewing gum gained worldwide popularity through American GIs in WWII, who were supplied chewing gum as a ration and traded it with locals. Synthetic gums were first introduced to the U. S. after chicle no longer satisfied the needs of making chewing gum
30.
Selenite (mineral)
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Selenite, satin spar, desert rose, and gypsum flower are four varieties of the mineral gypsum, all four varieties show obvious crystalline structure. The four crystalline varieties of gypsum are sometimes grouped together and called selenite, all varieties of gypsum, including selenite and alabaster, are composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. Selenite contains no significant selenium, the similarity of names comes from both substances being named from the Ancient Greek word for the Moon. The etymology of selenite is through Middle English selinete, from Latin selenites, from Greek selēnitēs, literally, moonstone or stone of the moon, the ancients had a belief that certain transparent crystals waxed and waned with the moon. From the 15th century, selenite has referred specifically to the variety of gypsum that occurs in transparent crystals or crystalline masses, all varieties of gypsum are very soft minerals. This is the most important identifying characteristic of gypsum, as any variety of gypsum can be scratched with a fingernail. Also, because gypsum has natural thermal insulating properties, all varieties feel warm to the touch, though sometimes grouped together as selenite, the four crystalline varieties have differences. General identifying descriptions of the related crystalline varieties are, most often transparent and colorless, crystal habit refers to the shapes that crystals exhibit. Selenite crystals commonly occur as tabular, reticular, and columnar crystals, often with no imperfections or inclusions, many collectible selenite crystals have interesting inclusions such as, accompanying related minerals, interior druse, dendrites, and fossils. In some rare instances, water was encased as a fluid inclusion when the crystal formed, selenite crystals sometimes form in thin tabular or mica-like sheets and have been used as glass panes as at Santa Sabina in Rome. Selenite crystals sometimes will also exhibit bladed rosette habit often with accompanying transparent, selenite crystals can be found both attached to a matrix or base rock, but can commonly be found as entire free-floating crystals, often in clay beds. Satin spar is almost always prismatic and fibrous in a crystal habit. Satin spar often occurs in seams, some of them quite long, desert roses are most often bladed, exhibiting the familiar shape of a rose, and almost always have an exterior druse. Desert roses are almost always unattached to a matrix or base rock, gypsum flowers are most often acicular, scaly, stellate, and lenticular. Selenite crystals can also exhibit “arrow/spear-head” as well as “duck-bill” twins, both selenite crystals and gypsum flowers sometimes form quite densely in acicular mats or nets, and can be quite brittle and fragile. Gypsum flowers are attached to a matrix or base rock. Gypsum crystals are colorless, white, gray, brown, beige, orange, pink, yellow, light red, and green. Colors are caused by the presence of mineral inclusions such as, copper ores, sulfur and sulfides, silver, iron ores, coal, calcite, dolomite
31.
Gypsum
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Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is widely mined and is used as a fertilizer, and as the constituent in many forms of plaster, blackboard chalk. Mohs scale of hardness, based on scratch Hardness comparison. It forms as a mineral and as a hydration product of anhydrite. The word gypsum is derived from the Greek word γύψος, plaster, because the quarries of the Montmartre district of Paris have long furnished burnt gypsum used for various purposes, this dehydrated gypsum became known as plaster of Paris. Upon addition of water, after a few tens of minutes plaster of Paris becomes regular gypsum again, causing the material to harden or set in ways that are useful for casting, Gypsum was known in Old English as spærstān, spear stone, referring to its crystalline projections. Gypsum may act as a source of sulfur for plant growth, which was discovered by J. M. Mayer, american farmers were so anxious to acquire it that a lively smuggling trade with Nova Scotia evolved, resulting in the so-called Plaster War of 1820. In the 19th century, it was known as lime sulfate or sulfate of lime. Gypsum is moderately water-soluble and, in contrast to most other salts, it exhibits retrograde solubility, when gypsum is heated in air it loses water and converts first to calcium sulfate hemihydrate, and, if heated further, to anhydrous calcium sulfate. As for anhydrite, its solubility in saline solutions and in brines is also dependent on NaCl concentration. Gypsum crystals are found to contain water and hydrogen bonding. Gypsum occurs in nature as flattened and often twinned crystals, and transparent, selenite contains no significant selenium, rather, both substances were named for the ancient Greek word for the Moon. Selenite may also occur in a silky, fibrous form, in case it is commonly called satin spar. Finally, it may also be granular or quite compact, in hand-sized samples, it can be anywhere from transparent to opaque. A very fine-grained white or lightly tinted variety of gypsum, called alabaster, is prized for ornamental work of various sorts, in arid areas, gypsum can occur in a flower-like form, typically opaque, with embedded sand grains called desert rose. It also forms some of the largest crystals found in nature, up to 12 m long, Gypsum is a common mineral, with thick and extensive evaporite beds in association with sedimentary rocks. Deposits are known to occur in strata from as far back as the Archaean eon, Gypsum is deposited from lake and sea water, as well as in hot springs, from volcanic vapors, and sulfate solutions in veins. Hydrothermal anhydrite in veins is commonly hydrated to gypsum by groundwater in near-surface exposures and it is often associated with the minerals halite and sulfur
32.
Silk
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Silk is a natural protein fiber, some forms of which can be woven into textiles. The protein fiber of silk is composed mainly of fibroin and is produced by insect larvae to form cocoons. The best-known silk is obtained from the cocoons of the larvae of the mulberry silkworm Bombyx mori reared in captivity, Silk is produced by several insects, but generally only the silk of moth caterpillars has been used for textile manufacturing. There has been research into other types of silk, which differ at the molecular level. Silk is mainly produced by the larvae of insects undergoing complete metamorphosis, Silk production also occurs in Hymenoptera, silverfish, mayflies, thrips, leafhoppers, beetles, lacewings, fleas, flies, and midges. Other types of arthropod produce silk, most notably various arachnids such as spiders, the word silk comes from Old English sioloc, from Greek σηρικός serikos, silken, ultimately from an Asian source. Several kinds of silk, which are produced by caterpillars other than the mulberry silkworm, have been known and used in China, South Asia. However, the scale of production was far smaller than for cultivated silks. Thus, the way to obtain silk suitable for spinning into textiles in areas where commercial silks are not cultivated was by tedious. Commercial silks originate from reared silkworm pupae, which are bred to produce a silk thread with no mineral on the surface. The pupae are killed by either dipping them in boiling water before the adult moths emerge or by piercing them with a needle. These factors all contribute to the ability of the cocoon to be unravelled as one continuous thread. Wild silks also tend to be difficult to dye than silk from the cultivated silkworm. Genetic modification of domesticated silkworms is used to facilitate the production of more types of silk. Silk fabric was first developed in ancient China, the earliest example of silk fabric is from 3630 BC, and it was used as wrapping for the body of a child from a Yangshao culture site in Qingtaicun at Xingyang, Henan. Legend gives credit for developing silk to a Chinese empress, Leizu, because of its texture and lustre, silk rapidly became a popular luxury fabric in the many areas accessible to Chinese merchants. Silk was in demand, and became a staple of pre-industrial international trade. In July 2007, archaeologists discovered intricately woven and dyed silk textiles in a tomb in Jiangxi province, Silk is described in a chapter on mulberry planting by Si Shengzhi of the Western Han
33.
Asbestos
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They are commonly known by their colors, as blue asbestos, brown asbestos, white asbestos, and green asbestos. It was used in applications as electrical insulation for hotplate wiring. When asbestos is used for its resistance to fire or heat and these desirable properties made asbestos very widely used. Prolonged inhalation of asbestos fibers can cause serious and fatal illnesses including cancer, mesothelioma. Concern of asbestos-related illness in modern times began in the 20th century, by the 1980s and 1990s, asbestos trade and use were heavily restricted, phased out, or banned outright in an increasing number of countries. S. History and a much lesser legal issue in most other countries involved, asbestos-related liability also remains an ongoing concern for many manufacturers, insurers and reinsurers. Asbestos derives from the ancient Greek ἄσβεστος, meaning unquenchable or inextinguishable, the word is pronounced /æsˈbɛstəs/, /æzˈbɛstəs/ or /æzˈbɛstɒs/. Six mineral types are defined by the United States Environmental Protection Agency as asbestos including those belonging to the serpentine class, all six asbestos mineral types are known to be human carcinogens. The visible fibers are themselves composed of millions of microscopic fibrils that can be released by abrasion. Chrysotile is the member of the serpentine class. 12001-29-5, is obtained from rocks which are common throughout the world. Its idealized chemical formula is Mg34, chrysotile appears under the microscope as a white fiber. Chrysotile has been used more than any type and accounts for about 95% of the asbestos found in buildings in America. Chrysotile is more flexible than amphibole types of asbestos, and can be spun, the most common use was corrugated asbestos cement roofing primarily for outbuildings, warehouses and garages. It may also be found in sheets or panels used for ceilings and sometimes for walls, chrysotile has been a component in joint compound and some plasters. Amosite, crocidolite, tremolite, anthophyllite and actinolite are members of the amphibole class, one formula given for amosite is Fe7Si8O222. Amosite is seen under a microscope as a grey-white vitreous fiber and it is found most frequently as a fire retardant in thermal insulation products, asbestos insulating board and ceiling tiles. 12001-28-4, is the form of the amphibole riebeckite, found primarily in southern Africa
34.
Ulexite
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Ulexite, sometimes known as TV rock, is a mineral occurring in silky white rounded crystalline masses or in parallel fibers. The natural fibers of ulexite conduct light along their long axes, ulexite was named for the German chemist Georg Ludwig Ulex who first discovered it. Ulexite is a complex mineral, with a basic structure containing chains of sodium, water. The chains are linked together by calcium, water, hydroxide and oxygen polyhedra, the boron units have a formula of 3– and a charge of −3. They are composed of three borate tetrahedra and two borate triangular groups, ulexite is found in evaporite deposits and the precipitated ulexite commonly forms a cotton ball tuft of acicular crystals. Ulexite is frequently associated with colemanite, borax, meyerhofferite, hydroboracite, probertite, glauberite, trona, mirabilite, calcite, gypsum. It is found principally in California and Nevada, US, Tarapacá Region in Chile, ulexite is also found in a vein-like bedding habit composed of closely packed fibrous crystals. Ulexite is also known as TV rock due to its optical characteristics. The fibers of ulexite act as optical fibers, transmitting light along their lengths by internal reflection, an interesting consequence is the generation of three cones, two of which are polarized, when a laser beam obliquely illuminates the fibers. These cones can be seen when viewing a light source through the mineral, ulexite is a borate mineral because its formula contains boron and oxygen. The isolated borate polyanion 3− has five boron atoms, therefore placing ulexite in the pentaborate group, borate minerals are rare because their main component, boron, only makes up less than 10 ppm of Earths crust. Because boron is an element, the majority of borate minerals occur only in one specific geologic environment. Borates are formed when boron bearing solutions, caused from the leaching of pyroclastic rocks, over time, borates deposit and form into stratified layers. Ulexite occurs in salt playas and dry lakes in association with large-scale gypsum deposits. There are no known polymorphs of ulexite nor does ulexite form a solid solution series with any other minerals, na, Ca, and Na-Ca borates are found in relation to ulexite. Crystals are rare, but will form fiborous, elongated crystals either oriented parallel or radial to each other, crystals may also be acicular, resembling needles. The point group of ulexite is 1, which means that the show very little symmetry as there are no rotational axes or mirror planes. The most common twinning plane is, ulexite collected from the Flat Bay gypsum quarry in Newfoundland exhibits acicular cottonballs of crystals with a nearly square cross section formed by the equal development of two pinacoids
35.
Sphalerite
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Sphalerite is a mineral that is the chief ore of zinc. It consists largely of zinc sulfide in crystalline form but almost always contains variable iron, when iron content is high it is an opaque black variety, marmatite. It is usually found in association with galena, pyrite, and other sulfides along with calcite, dolomite, miners have also been known to refer to sphalerite as zinc blende, black-jack, and ruby jack. The mineral crystallizes in the crystal system. In the crystal structure, zinc and sulfur atoms are tetrahedrally coordinated, the structure is closely related to the structure of diamond. The hexagonal analog is known as the wurtzite structure, the lattice constant for zinc sulfide in the zinc blende crystal structure is 0.541 nm, calculated from geometry and ionic radii of 0.074 nm and 0.184 nm. Its color is yellow, brown, or gray to gray-black. Its luster is adamantine, resinous to submetallic for high iron varieties and it has a yellow or light brown streak, a Mohs hardness of 3. 5–4, and a specific gravity of 3. 9–4.1. Some specimens have a red iridescence within the crystals, these are called ruby sphalerite. The pale yellow and red varieties have very little iron and are translucent, the darker, more opaque varieties contain more iron. Some specimens are also fluorescent in ultraviolet light, the refractive index of sphalerite is 2.37. Sphalerite crystallizes in the crystal system and possesses perfect dodecahedral cleavage. Gemmy, pale specimens from Franklin, New Jersey, are highly fluorescent orange and/or blue under ultraviolet light and are known as cleiophane. Sphalerite is the ore of zinc and is found in thousands of locations worldwide. Sources of high quality crystals include, Freiberg, Saxony, and Neudorf, Harz Mountains of Germany The Lengenbach Quarry, Binntal, Valais, freshly cut gems have an adamantine luster. Owing to their softness and fragility the gems are often left unset as collectors or museum pieces, gem-quality material is usually a yellowish to honey brown, red to orange, or green. List of minerals Danas Manual of Mineralogy ISBN 0-471-03288-3 Webster, R. Read, P. G. Gems, Their sources, descriptions and identification, p.386. ISBN 0-7506-1674-1 Minerals. net Minerals of Franklin, NJ The sphalerite structure Possible relation of Sphalerite to origins of life and precursor chemicals in Primordial Soup
36.
Cinnabar
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Cinnabar generally occurs as a vein-filling mineral associated with recent volcanic activity and alkaline hot springs. The mineral resembles quartz in symmetry and in its exhibiting birefringence, cinnabar has a refractive index of ~3.2. The color and properties derive from a structure that is a crystalline lattice belonging to the hexagonal crystal system. Associated modern precautions for use and handling of cinnabar arise from the toxicity of the mercury component, the name comes from Ancient Greek, κιννάβαρι, a Greek word most likely applied by Theophrastus to several distinct substances. Other sources say the word comes from the Persian, شنگرف shangarf, in Latin it was sometimes known as minium, meaning also red cinnamon, though both of these terms now refer specifically to lead tetroxide. Cinnabar is generally found in a massive, granular or earthy form and is bright scarlet to brick-red in color and it resembles quartz in its symmetry. It exhibits birefringence, and it has the highest refractive index of any mineral and its mean refractive index is 3.08, versus the indices for diamond and the non-mineral gallium arsenide, which are 2.42 and 3.93, respectively. The hardness of cinnabar is 2. 0–2.5 on the Mohs scale, structurally, cinnabar belongs to the trigonal crystal system. It occurs as thick tabular or slender prismatic crystals or as granular to massive incrustations, crystal twinning occurs as simple contact twins. Note, mercury sulfide, HgS, adopts the structure described. Cinnabar is the stable form, and is a structure akin to that of HgO. In addition, HgS is found in a black, non-cinnabar polymorph that has the zincblende structure, Cinnabar generally occurs as a vein-filling mineral associated with recent volcanic activity and alkaline hot springs. Cinnabar is deposited by epithermal ascending aqueous solutions far removed from their igneous source and it is associated with native mercury, stibnite, realgar, pyrite, marcasite, opal, quartz, chalcedony, dolomite, calcite and barite. Cinnabar is essentially found in all mineral extraction localities that yield mercury, notably Puerto Princesa, Almadén, New Almaden, Hastings Mine and it was also mined near Red Devil, Alaska on the middle Kuskokwim River. Red Devil was named after the Red Devil cinnabar mine, a source of mercury. It has been found in Dominica near its sulfur springs at the end of the island along the west coast. Cinnabar is still being deposited, e. g. at the present day from the hot waters of Sulphur Bank Mine in California and Steamboat Springs, Nevada. As the most common source of mercury in nature, cinnabar has been mined for thousands of years, during the Roman Empire it was mined both as a pigment, and for its mercury content
37.
Cuprite
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Cuprite is an oxide mineral composed of copper oxide Cu2O, and is a minor ore of copper. Its dark crystals with red reflections are in the isometric system hexoctahedral class, appearing as cubic, octahedral, or dodecahedral forms. In spite of its color it is rarely used for jewelry because of its low Mohs hardness of 3.5 to 4. It has a high specific gravity of 6.1, imperfect cleavage. The luster is sub-metallic to brilliant adamantine, the chalcotrichite variety typically shows greatly elongated capillary or needle like crystals forms. It is a mineral which forms in the oxidized zone of copper sulfide deposits. It frequently occurs in association with native copper, azurite, chrysocolla, malachite, tenorite and it is known as ruby copper due to its distinctive red color. Cuprite was first described in 1845 and the name derives from the Latin cuprum for its copper content, cuprite is found in the Ural Mountains, Altai Mountains, and Sardinia, and in more isolated locations in Cornwall, France, Arizona, Chile, Bolivia, and Namibia. Virtually every faceted stone over one carat in weight is from this single deposit, only the gems soft nature prevents it from being among the most valuable jewelry stones
38.
Quartz
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Quartz is the second most abundant mineral in Earths continental crust, behind feldspar. There are many different varieties of quartz, several of which are semi-precious gemstones, since antiquity, varieties of quartz have been the most commonly used minerals in the making of jewelry and hardstone carvings, especially in Eurasia. The word quartz is derived from the German word Quarz and its Middle High German ancestor twarc, the Ancient Greeks referred to quartz as κρύσταλλος derived from the Ancient Greek κρύος meaning icy cold, because some philosophers apparently believed the mineral to be a form of supercooled ice. Today, the rock crystal is sometimes used as an alternative name for the purest form of quartz. Quartz belongs to the crystal system. The ideal crystal shape is a six-sided prism terminating with six-sided pyramids at each end, well-formed crystals typically form in a bed that has unconstrained growth into a void, usually the crystals are attached at the other end to a matrix and only one termination pyramid is present. However, doubly terminated crystals do occur where they develop freely without attachment, a quartz geode is such a situation where the void is approximately spherical in shape, lined with a bed of crystals pointing inward. α-quartz crystallizes in the crystal system, space group P3121 and P3221 respectively. β-quartz belongs to the system, space group P6222 and P6422. These space groups are truly chiral, both α-quartz and β-quartz are examples of chiral crystal structures composed of achiral building blocks. The transformation between α- and β-quartz only involves a comparatively minor rotation of the tetrahedra with respect to one another, although many of the varietal names historically arose from the color of the mineral, current scientific naming schemes refer primarily to the microstructure of the mineral. Color is an identifier for the cryptocrystalline minerals, although it is a primary identifier for the macrocrystalline varieties. Pure quartz, traditionally called rock crystal or clear quartz, is colorless and transparent or translucent, common colored varieties include citrine, rose quartz, amethyst, smoky quartz, milky quartz, and others. The most important distinction between types of quartz is that of macrocrystalline and the microcrystalline or cryptocrystalline varieties, the cryptocrystalline varieties are either translucent or mostly opaque, while the transparent varieties tend to be macrocrystalline. Chalcedony is a form of silica consisting of fine intergrowths of both quartz, and its monoclinic polymorph moganite. Other opaque gemstone varieties of quartz, or mixed rocks including quartz, often including contrasting bands or patterns of color, are agate, carnelian or sard, onyx, heliotrope, amethyst is a form of quartz that ranges from a bright to dark or dull purple color. The worlds largest deposits of amethysts can be found in Brazil, Mexico, Uruguay, Russia, France, Namibia, sometimes amethyst and citrine are found growing in the same crystal. It is then referred to as ametrine, an amethyst is formed when there is iron in the area where it was formed
39.
Calcite
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Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate. The Mohs scale of hardness, based on scratch hardness comparison. Other polymorphs of calcium carbonate are the minerals aragonite and vaterite, aragonite will change to calcite at 380–470 °C, and vaterite is even less stable. Calcite is derived from the German Calcit, a term coined in the 19th century from the Latin word for lime and it is thus etymologically related to chalk. Calcite crystals are trigonal-rhombohedral, though actual calcite rhombohedra are rare as natural crystals, however, they show a remarkable variety of habits including acute to obtuse rhombohedra, tabular forms, prisms, or various scalenohedra. Calcite exhibits several twinning types adding to the variety of observed forms and it may occur as fibrous, granular, lamellar, or compact. Cleavage is usually in three directions parallel to the rhombohedron form and its fracture is conchoidal, but difficult to obtain. It has a defining Mohs hardness of 3, a gravity of 2.71. Color is white or none, though shades of gray, red, orange, yellow, green, blue, violet, brown, calcite is transparent to opaque and may occasionally show phosphorescence or fluorescence. A transparent variety called Iceland spar is used for optical purposes, acute scalenohedral crystals are sometimes referred to as dogtooth spar while the rhombohedral form is sometimes referred to as nailhead spar. Single calcite crystals display an optical property called birefringence and this strong birefringence causes objects viewed through a clear piece of calcite to appear doubled. The birefringent effect was first described by the Danish scientist Rasmus Bartholin in 1669, at a wavelength of ~590 nm calcite has ordinary and extraordinary refractive indices of 1.658 and 1.486, respectively. Between 190 and 1700 nm, the refractive index varies roughly between 1.9 and 1.5, while the extraordinary refractive index varies between 1.6 and 1.4. Calcite, like most carbonates, will dissolve with most forms of acid, calcite can be either dissolved by groundwater or precipitated by groundwater, depending on several factors including the water temperature, pH, and dissolved ion concentrations. Although calcite is fairly insoluble in water, acidity can cause dissolution of calcite. Ambient carbon dioxide, due to its acidity, has a slight solubilizing effect on calcite, calcite exhibits an unusual characteristic called retrograde solubility in which it becomes less soluble in water as the temperature increases. When conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together or it can fill fractures. On a landscape scale, continued dissolution of calcium carbonate-rich rocks can lead to the expansion and eventual collapse of cave systems, high-grade optical calcite was used in World War II for gun sights, specifically in bomb sights and anti-aircraft weaponry
40.
Topaz
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Topaz is a silicate mineral of aluminium and fluorine with the chemical formula Al2SiO42. Topaz crystallizes in the system, and its crystals are mostly prismatic terminated by pyramidal. Pure topaz is colorless and transparent but is usually tinted by impurities, typical topaz is wine red, yellow, pale gray, reddish-orange and it can also be white, pale green, blue, gold, pink, reddish-yellow or opaque to transparent/translucent. Orange topaz, also known as precious topaz, is the traditional November birthstone, the symbol of friendship, Imperial topaz is yellow, pink or pink-orange. Brazilian Imperial Topaz can often have a yellow to deep golden brown hue. Many brown or pale topazes are treated to make them bright yellow, gold, some imperial topaz stones can fade on exposure to sunlight for an extended period of time. Blue topaz is the gemstone of the US state of Texas. Naturally occurring blue topaz is quite rare, typically, colorless, gray or pale yellow and blue material is heat treated and irradiated to produce a more desired darker blue. Mystic topaz is colorless topaz which has been artificially coated giving it the desired rainbow effect, Topaz is commonly associated with silicic igneous rocks of the granite and rhyolite type. It typically crystallizes in granitic pegmatites or in cavities in rhyolite lava flows including those at Topaz Mountain in western Utah. Brazil is one of the largest producers of topaz, some clear topaz crystals from Brazilian pegmatites can reach boulder size, crystals of this size may be seen in museum collections. The Topaz of Aurangzeb, observed by Jean Baptiste Tavernier weighed 157.75 carats, the American Golden Topaz, a more recent gem, weighed a massive 22,892.5 carats. Large, vivid blue topaz specimens from the St. Anns mine in Zimbabwe were found in the late 1980s, colorless and light-blue varieties of topaz are found in Precambrian granite in Mason County, Texas within the Llano Uplift. There is no mining of topaz in that area. Pliny said that Topazos is an island in the Red Sea. Alternatively, the word topaz may be related to the Sanskrit word तपस् tapas, nicols, the author of one of the first systematic treatises on minerals and gemstones, dedicated two chapters to the topic in 1652. In the Middle Ages, the name topaz was used to refer to any yellow gemstone, many modern English translations of the Bible, including the King James Version mention topaz. The masoretic text has pitdah as the gem the stone is made from, more likely, pitdah is derived from Sanskrit words, meaning yellow burn or, metaphorically, fiery
41.
Beryl
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Beryl is a mineral composed of beryllium aluminium cyclosilicate with the chemical formula Be3Al26. Well-known varieties of beryl include emerald and aquamarine, naturally occurring, hexagonal crystals of beryl can be up to several meters in size, but terminated crystals are relatively rare. Pure beryl is colorless, but it is tinted by impurities, possible colors are green, blue, yellow, red. The name beryl is derived from Greek βήρυλλος beryllos which referred to a precious blue-green color-of-sea-water stone, akin to Prakrit verulia, the term was later adopted for the mineral beryl more exclusively. When the first eyeglasses were constructed in 13th century Italy, the lenses were made of beryl as glass could not be clear enough. Consequently glasses were named Brillen in German, beryl of various colors is found most commonly in granitic pegmatites, but also occurs in mica schists in the Ural Mountains, and limestone in Colombia. Beryl is often associated with tin and tungsten ore bodies, beryl is found in Europe in Norway, Austria, Germany, Sweden, Ireland and Russia, as well as Brazil, Colombia, Madagascar, Mozambique, Pakistan, South Africa, the United States, and Zambia. US beryl locations are in California, Colorado, Connecticut, Georgia, Idaho, Maine, New Hampshire, North Carolina, South Dakota and Utah. As of 1999, the worlds largest known naturally occurring crystal of any mineral is a crystal of beryl from Malakialina, Madagascar,18 m long and 3.5 m in diameter, aquamarine is a blue or cyan variety of beryl. It occurs at most localities which yield ordinary beryl, the gem-gravel placer deposits of Sri Lanka contain aquamarine. Clear yellow beryl, such as occurring in Brazil, is sometimes called aquamarine chrysolite. The deep blue version of aquamarine is called maxixe, maxixe is commonly found in the country of Madagascar. Its color fades to white when exposed to sunlight or is subjected to heat treatment, the pale blue color of aquamarine is attributed to Fe2+. Fe3+ ions produce golden-yellow color, and when both Fe2+ and Fe3+ are present, the color is a darker blue as in maxixe, decoloration of maxixe by light or heat thus may be due to the charge transfer between Fe3+ and Fe2+. Dark-blue maxixe color can be produced in green, pink or yellow beryl by irradiating it with high-energy particles, in the United States, aquamarines can be found at the summit of Mt. Antero in the Sawatch Range in central Colorado. In Wyoming, aquamarine has been discovered in the Big Horn Mountains, another location within the United States is the Sawtooth Range near Stanley, Idaho, although the minerals are within a wilderness area which prevents collecting. In Brazil, there are mines in the states of Minas Gerais, Espírito Santo, and Bahia, the mines of Colombia, Zambia, Madagascar, Malawi, Tanzania and Kenya also produce aquamarine. The largest aquamarine of gemstone quality ever mined was found in Marambaia, Minas Gerais, Brazil and it weighed over 110 kg, and its dimensions were 48.5 cm long and 42 cm in diameter
42.
Tourmaline
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Tourmaline is a crystalline boron silicate mineral compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline is classified as a stone and the gemstone comes in a wide variety of colors. The name comes from the Tamil and Sinhalese word Turmali or Thoramalli, brightly colored Sri Lankan gem tourmalines were brought to Europe in great quantities by the Dutch East India Company to satisfy a demand for curiosities and gems. At the time it was not realised that schorl and tourmaline were the same mineral, tourmaline was sometimes called the Ceylonese Magnet because it could attract and then repel hot ashes due to its pyroelectric properties. Tourmalines were used by chemists in the 19th century to light by shining rays onto a cut. It may account for 95% or more of all tourmaline in nature, the early history of the mineral schorl shows that the name schorl was in use prior to 1400 because a village known today as Zschorlau was then named Schorl. This village had a tin mine where, in addition to cassiterite. The first description of schorl with the name schürl and its occurrence was written by Johannes Mathesius in 1562 under the title Sarepta oder Bergpostill, up to about 1600, additional names used in the German language were Schurel, Schörle, and Schurl. Beginning in the 18th century, the name Schörl was mainly used in the German-speaking area, in English, the names shorl and shirl were used in the 18th century. In the 19th century the names common schorl, schörl, schorl, dravite, also called brown tourmaline, is the sodium magnesium rich tourmaline endmember. Uvite, in comparison, is a calcium magnesium tourmaline, dravite forms multiple series, with other tourmaline members, including schorl and elbaite. Today this tourmaline locality at Dravograd, is a part of the Republic of Slovenia, tschermak gave this tourmaline the name dravite, for the Drava river area, which is the district along the Drava River in Austria and Slovenia. Dravite varieties include the green chromium dravite and the vanadium dravite. A lithium-tourmaline elbaite was one of three pegmatitic minerals from Utö, Sweden, in which the new alkali element lithium was determined in 1818 by Johan August Arfwedson for the first time. Elba Island, Italy, was one of the first localities where colored, in 1850 Karl Friedrich August Rammelsberg described fluorine in tourmaline for the first time. In 1870 he proved that all varieties of tourmaline contain chemically bound water, in 1889 Scharitzer proposed the substitution of by F in red Li-tourmaline from Sušice, Czech Republic. In 1914 Vladimir Vernadsky proposed the name Elbait for lithium-, sodium-, most likely the type material for elbaite was found at Fonte del Prete, San Piero in Campo, Campo nellElba, Elba Island, Province of Livorno, Tuscany, Italy. In 1933 Winchell published a formula for elbaite, H8Na2Li3Al3B6Al12Si12O62
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Fluorite
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Fluorite is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals and it crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon. Mohs scale of hardness, based on scratch Hardness comparison. Fluorite is a mineral, both in visible and ultraviolet light, and the stone has ornamental and lapidary uses. Industrially, fluorite is used as a flux for smelting, and in the production of certain glasses, the purest grades of fluorite are a source of fluoride for hydrofluoric acid manufacture, which is the intermediate source of most fluorine-containing fine chemicals. Optically clear transparent fluorite lenses have low dispersion, so made from it exhibit less chromatic aberration. Fluorite optics are also usable in the range, where conventional glasses are too absorbent for use. The word fluorite is derived from the Latin verb fluere, meaning to flow, the mineral is used as a flux in iron smelting to decrease the viscosity of slags. The term flux comes from the Latin adjective fluxus, meaning flowing, loose, agricola, a German scientist with expertise in philology, mining, and metallurgy, named fluorspar as a neo-Latinization of the German Flussspat from Fluß and Spat. In 1852, fluorite gave its name to the phenomenon of fluorescence, Fluorite also gave the name to its constitutive element fluorine. Presently, the fluorspar is most commonly used for fluorite as the industrial and chemical commodity, while fluorite is used mineralogically. Fluorite crystallises in a cubic motif, crystal twinning is common and adds complexity to the observed crystal habits. Fluorite has four perfect cleavage planes that help produce octahedral fragments, element substitution for the calcium cation often includes certain rare earth elements, such as yttrium and cerium. Iron, sodium, and barium are also common impurities, some fluorine may be replaced by the chloride anion. Fluorite is a widely occurring mineral that occurs globally with significant deposits in over 9,000 areas. It may occur as a deposit, especially with metallic minerals, where it often forms a part of the gangue and may be associated with galena, sphalerite, barite, quartz. It is a mineral in deposits of hydrothermal origin and has been noted as a primary mineral in granites and other igneous rocks. The world reserves of fluorite are estimated at 230 million tonnes with the largest deposits being in South Africa, Mexico, China is leading the world production with about 3 Mt annually, followed by Mexico, Mongolia, Russia, South Africa, Spain and Namibia
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Jade
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Jade is an ornamental green rock. The middle member of series with an intermediate composition is called actinolite. The higher the content, the greener the colour. Jadeite is a sodium- and aluminium-rich pyroxene, the precious form of jadeite jade is a microcrystalline interlocking growth of jadeite crystals. The English word jade is derived from the Spanish term piedra de ijada or loin stone, from its reputed efficacy in curing ailments of the loins, nephrite is derived from lapis nephriticus, a Latin translation of the Spanish piedra de ijada. Nephrite and jadeite were used from prehistoric periods for hardstone carving, jadeite has about the same hardness as quartz. Nephrite is slightly softer but tougher than jadeite and it was not until the 19th century that a French mineralogist, Alexis Damour, determined that jade was in fact two different minerals. Among the earliest known jade artifacts excavated from prehistoric sites are simple ornaments with bead, button, additionally, jade was used for adze heads, knives, and other weapons, which can be delicately shaped. As metal-working technologies became available, the beauty of jade made it valuable for ornaments and decorative objects. Jadeite measures between 6.0 and 7.0 Mohs hardness, and nephrite between 6.0 and 6.5, so it can be worked with quartz or garnet sand, of the two, jadeite is rarer, documented in fewer than 12 places worldwide. Translucent emerald-green jadeite is the most prized variety, both historically and today, Burma and Guatemala are the principal sources of modern gem jadeite. In the area of Mogaung in the Myitkyina District of Upper Burma, jadeite formed a layer in the dark-green serpentine, Canada provides the major share of modern lapidary nephrite. Nephrite jade was used mostly in pre-1800 China as well as in New Zealand, the Pacific Coast and the Atlantic Coast of North America, Neolithic Europe, in addition to Mesoamerica, jadeite was used by Neolithic Japanese and European cultures. Dushan Jade was being mined as early as 6000 BC, in the Yin Ruins of the Shang Dynasty in Anyang, Dushan Jade ornaments were unearthed in the tomb of the Shang kings. Jade was used to create many utilitarian and ceremonial objects, from indoor decorative items to jade burial suits, Jade was considered the imperial gem. There, white and greenish nephrite jade is found in quarries and as pebbles. The river jade collection is concentrated in the Yarkand, the White Jade, jadeite, with its bright emerald-green, pink, lavender, orange and brown colours was imported from Burma to China only after about 1800. The vivid green variety became known as Feicui or Kingfisher Jade, in the history of the art of the Chinese empire, jade has had a special significance, comparable with that of gold and diamonds in the West
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Wax
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Waxes are a diverse class of organic compounds that are hydrophobic, malleable solids near ambient temperatures. They include higher alkanes and lipids, typically with melting points above about 40 °C, waxes are insoluble in water but soluble in organic, nonpolar solvents. Natural waxes of different types are produced by plants and animals, waxes are organic compounds that characteristically consist of long alkyl chains. They may also include various groups such as fatty acids, primary and secondary long chain alcohols, unsaturated bonds, aromatics, amides, ketones. They frequently contain fatty acid esters as well, synthetic waxes are often long-chain hydrocarbons that lack functional groups. Waxes are synthesized by plants and animals. Those of animal origin typically consist of wax esters derived from a variety of carboxylic acids, in waxes of plant origin characteristic mixtures of unesterified hydrocarbons may predominate over esters. The composition depends not only on species, but also on location of the organism. The most commonly known animal wax is beeswax, but other insects secrete waxes, a major component of the beeswax used in constructing honeycombs is the ester myricyl palmitate which is an ester of triacontanol and palmitic acid. Its melting point is 62-65 °C, spermaceti occurs in large amounts in the head oil of the sperm whale. One of its constituents is cetyl palmitate, another ester of a fatty acid. Lanolin is a wax obtained from wool, consisting of esters of sterols, plants secrete waxes into and on the surface of their cuticles as a way to control evaporation, wettability and hydration. From the commercial perspective, the most important plant wax is carnauba wax, containing the ester myricyl cerotate, it has many applications, such as confectionery and other food coatings, car and furniture polish, floss coating, and surfboard wax. Other more specialized vegetable waxes include candelilla wax and ouricury wax, plant and animal based waxes or oils can undergo selective chemical modifications to produce waxes with more desirable properties than are available in the unmodified starting material. This approach has relied on green chemistry approaches including olefin metathesis and enzymatic reactions, although many natural waxes contain esters, paraffin waxes are hydrocarbons, mixtures of alkanes usually in a homologous series of chain lengths. These materials represent a significant fraction of petroleum and they are refined by vacuum distillation. Paraffin waxes are mixtures of saturated n- and iso- alkanes, naphthenes, a typical alkane paraffin wax chemical composition comprises hydrocarbons with the general formula CnH2n+2, such as Hentriacontane, C31H64. The degree of branching has an important influence on the properties, millions of tons of paraffin waxes are produced annually
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Chalcedony
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Chalcedony is a cryptocrystalline form of silica, composed of very fine intergrowths of quartz and moganite. These are both silica minerals, but they differ in that quartz has a crystal structure, while moganite is monoclinic. Chalcedonys standard chemical structure is SiO2, Chalcedony has a waxy luster, and may be semitransparent or translucent. It can assume a range of colors, but those most commonly seen are white to gray. The color of chalcedony sold commercially is often enhanced by dyeing or heating, the name chalcedony comes from the Latin chalcedonius. The name appears in Pliny the Elders Naturalis Historia as a term for a kind of Jaspis. The name is derived from the town Chalcedon in Asia Minor. The Greek word khalkedon also appears in the Book of Revelation and it is a hapax legomenon so it is hard to tell whether the precious gem mentioned in the Bible is the same mineral known by this name today. Chalcedony occurs in a range of varieties. Many semi-precious gemstones are in forms of chalcedony. The more notable varieties of chalcedony are as follows, Agate is a variety of chalcedony characterized by either transparency or color patterns, opaque varieties are sometimes referred to as jasper. Fire agate shows iridescent phenomena on a background, iris agate shows exceptional iridescence when light is shone through the stone. Landscape agate is chalcedony with a number of different mineral impurities making the stone resemble landscapes, aventurine is a form of quartz, characterised by its translucency and the presence of platy mineral inclusions that give a shimmering or glistening effect termed aventurescence. Chrome-bearing fuchsite is the inclusion, and gives a silvery green or blue sheen. Oranges and browns are attributed to hematite or goethite, carnelian is a clear-to-translucent reddish-brown variety of chalcedony. Its hue may vary from an orange, to an intense almost-black coloration. Similar to carnelian is sard, which is rather than red. Chrysoprase is a variety of chalcedony, which has been colored by nickel oxide
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Cabochon
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A cabochon, from the Middle French word caboche, is a gemstone which has been shaped and polished as opposed to faceted. The resulting form is usually a convex obverse with a flat reverse, cutting en cabochon is usually applied to opaque gems, while faceting is usually applied to transparent stones. Hardness is also taken into account as softer gemstones with a lower than 7 on the Mohs hardness scale are easily scratched, mainly by silicon dioxide in dust. This would quickly make translucent gems unattractive—instead they are polished as cabochons, the usual shape for cutting cabochons is an ellipse. An exception is cabochons on some watches crowns, which are round, the procedure is to cut a slab of the rough rock with a slab saw, and next to stencil a shape from a template. The slab is then trimmed near the line using a diamond blade saw—called a trim saw. Diamond impregnated wheels or silicon carbide wheels can be used to grind the rock down. Most lapidary workshops and production facilities have moved away from silicon carbide to diamond grinding wheels or flat lap disks, once the piece is trimmed it can be dopped or completed by hand. Dopping is normally done by adhering the stone with hard wax onto a length of wooden dowel called a dop stick, the piece is then ground to the template line, the back edges may be bevelled, and finally the top is sanded and polished to a uniform dome
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Sapphire
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Sapphire is a gemstone, a variety of the mineral corundum, an aluminium oxide. It is typically blue in color, but natural fancy sapphires also occur in yellow, purple, orange, the only color which sapphire cannot be is red - as red colored corundum is called ruby, another corundum variety. This variety in color is due to amounts of elements such as iron, titanium, chromium, copper. Commonly, natural sapphires are cut and polished into gemstones and worn in jewelry and they also may be created synthetically in laboratories for industrial or decorative purposes in large crystal boules. Sapphire is the birthstone for September and the gem of the 45th anniversary, a sapphire jubilee occurs after 65 years. Sapphire is one of the two gem-varieties of corundum, the other being ruby, although blue is the best-known sapphire color, they occur in other colors, including gray and black, and they can be colorless. A a pinkish orange variety of sapphire is called padparadscha, significant sapphire deposits are found in Eastern Australia, Thailand, Sri Lanka, China, Madagascar, East Africa, and in North America in a few locations, mostly in Montana. Sapphire and rubies are often found in the geological setting. Every sapphire mine produces a range of quality - and origin is not a guarantee of quality. For sapphire, Kashmir receives the highest premium although Burma, Sri Lanka, the cost of natural sapphires varies depending on their color, clarity, size, cut, and overall quality. For gems of exceptional quality, an independent determination from a respected laboratory such as the GIA, gemstone color can be described in terms of hue, saturation, and tone. Hue is commonly understood as the color of the gemstone, saturation refers to the vividness or brightness of the hue, and tone is the lightness to darkness of the hue. Blue sapphire exists in various mixtures of its primary and secondary hues, various tonal levels, blue sapphires are evaluated based upon the purity of their primary hue. Purple, violet, and green are the most common secondary hues found in blue sapphires, violet and purple can contribute to the overall beauty of the color, while green is considered to be distinctly negative. Blue sapphires with up to 15% violet or purple are generally said to be of fine quality, gray is the normal saturation modifier or mask found in blue sapphires. Gray reduces the saturation or brightness of the hue, and therefore has a negative effect. The 423-carat Logan sapphire in the National Museum of Natural History, in Washington, sapphires in colors other than blue are called fancy or parti colored sapphires. Fancy sapphires are found in yellow, orange, green sapphires, brown, purple
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Ruby
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A ruby is a pink to blood-red colored gemstone, a variety of the mineral corundum. Other varieties of gem-quality corundum are called sapphires, Ruby is one of the traditional cardinal gems, together with amethyst, sapphire, emerald, and diamond. They word ruby comes from ruber, Latin for red, the color of a ruby is due to the element chromium. The quality of a ruby is determined by its color, cut, and clarity, the brightest and most valuable red called blood-red or pigeon blood, commands a large premium over other rubies of similar quality. After color follows clarity, similar to diamonds, a stone will command a premium. Ruby is the birthstone for July and is usually more pink than garnet. The worlds most expensive ruby is the Sunrise Ruby, rubies have a hardness of 9.0 on the Mohs scale of mineral hardness. Among the natural gems only moissanite and diamond are harder, with diamond having a Mohs hardness of 10.0, when a chromium atom replaces an occasional aluminum atom, it too loses 3 electrons to become a chromium3+ ion to maintain the charge balance of the Al2O3 crystal. However, the Cr3+ ions are larger and have electron orbitals in different directions than aluminum, the octahedral arrangement of the O2− ions is distorted, and the energy levels of the different orbitals of those Cr3+ ions are slightly altered because of the directions to the O2− ions. Those energy differences correspond to absorption in the ultraviolet, violet, if one percent of the aluminum ions are replaced by chromium in ruby, the yellow-green absorption results in a red color for the gem. Additionally, absorption at any of the above wavelengths stimulates fluorescent emission of 694-nanometer-wavelength red light, after absorbing short-wavelength light, there is short interval of time when the crystal lattice of ruby is in an excited state before fluorescence occurs. If 694-nanometer photons pass through the crystal during that time, they can stimulate more fluorescent photons to be emitted in-phase with them, thus strengthening the intensity of that red light. By arranging mirrors or other means to pass emitted light repeatedly through the crystal, all natural rubies have imperfections in them, including color impurities and inclusions of rutile needles known as silk. Gemologists use these needle inclusions found in natural rubies to distinguish them from synthetics, simulants, usually, the rough stone is heated before cutting. These days, almost all rubies are treated in some form, untreated rubies of high quality command a large premium. Some rubies show a three-point or six-point asterism or star and these rubies are cut into cabochons to display the effect properly. Asterisms are best visible with a source and move across the stone as the light moves or the stone is rotated. Such effects occur when light is reflected off the silk in a certain way and this is one example where inclusions increase the value of a gemstone
