1.
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
2.
Crystallography
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Crystallography is the experimental science of determining the arrangement of atoms in the crystalline solids. The word crystallography derives from the Greek words crystallon cold drop, frozen drop, with its meaning extending to all solids with some degree of transparency, and graphein to write. In July 2012, the United Nations recognised the importance of the science of crystallography by proclaiming that 2014 would be the International Year of Crystallography, X-ray crystallography is used to determine the structure of large biomolecules such as proteins. Before the development of X-ray diffraction crystallography, the study of crystals was based on measurements of their geometry. This involved measuring the angles of crystal faces relative to other and to theoretical reference axes. This physical measurement is carried out using a goniometer, the position in 3D space of each crystal face is plotted on a stereographic net such as a Wulff net or Lambert net. The pole to face is plotted on the net. Each point is labelled with its Miller index, the final plot allows the symmetry of the crystal to be established. Crystallographic methods now depend on analysis of the patterns of a sample targeted by a beam of some type. X-rays are most commonly used, other beams used include electrons or neutrons and this is facilitated by the wave properties of the particles. Crystallographers often explicitly state the type of beam used, as in the terms X-ray crystallography and these three types of radiation interact with the specimen in different ways. X-rays interact with the distribution of electrons in the sample. Electrons are charged particles and therefore interact with the charge distribution of both the atomic nuclei and the electrons of the sample. Neutrons are scattered by the atomic nuclei through the nuclear forces, but in addition. They are therefore also scattered by magnetic fields, when neutrons are scattered from hydrogen-containing materials, they produce diffraction patterns with high noise levels. However, the material can sometimes be treated to substitute deuterium for hydrogen, because of these different forms of interaction, the three types of radiation are suitable for different crystallographic studies. An image of an object is made using a lens to focus the beam. However, the wavelength of light is three orders of magnitude longer than the length of typical atomic bonds and atoms themselves
3.
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
4.
Gemstone
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A gemstone is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks or organic materials that are not minerals are used for jewelry and are therefore often considered to be gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry because of their luster or other properties that have aesthetic value. Rarity is another characteristic that lends value to a gemstone, apart from jewelry, from earliest antiquity engraved gems and hardstone carvings, such as cups, were major luxury art forms. A gem maker is called a lapidary or gemcutter, a worker is a diamantaire. The carvings of Carl Fabergé are significant works in this tradition, the traditional classification in the West, which goes back to the ancient Greeks, begins with a distinction between precious and semi-precious, similar distinctions are made in other cultures. In modern usage the precious stones are diamond, ruby, sapphire, other stones are classified by their color, translucency and hardness. Another unscientific term for semi-precious gemstones used in art history and archaeology is hardstone, in modern times gemstones are identified by gemologists, who describe gems and their characteristics using technical terminology specific to the field of gemology. The first characteristic a gemologist uses to identify a gemstone is its chemical composition, for example, diamonds are made of carbon and rubies of aluminium oxide. Next, many gems are crystals which are classified by their crystal system such as cubic or trigonal or monoclinic, another term used is habit, the form the gem is usually found in. For example, diamonds, which have a crystal system, are often found as octahedrons. Gemstones are classified into different groups, species, and varieties, for example, ruby is the red variety of the species corundum, while any other color of corundum is considered sapphire. Other examples are the Emerald, aquamarine, red beryl, goshenite, heliodor, and morganite, gems are characterized in terms of refractive index, dispersion, specific gravity, hardness, cleavage, fracture, and luster. They may exhibit pleochroism or double refraction and they may have luminescence and a distinctive absorption spectrum. Material or flaws within a stone may be present as inclusions, gemstones may also be classified in terms of their water. This is a grading of the gems luster, transparency. Very transparent gems are considered first water, while second or third water gems are those of a lesser transparency, there is no universally accepted grading system for gemstones. Diamonds are graded using a system developed by the Gemological Institute of America in the early 1950s, historically, all gemstones were graded using the naked eye
5.
Brilliant (diamond cut)
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A brilliant is a diamond or other gemstone cut in a particular form with numerous facets so as to have exceptional brilliance. The shape resembles that of a cone and provides maximized light return through the top of the diamond, even with modern techniques, the cutting and polishing of a diamond crystal always result in a dramatic loss of weight, rarely is it less than 50%. The round brilliant cut is preferred when the crystal is an octahedron, oddly shaped crystals such as macles are more likely to be cut in a fancy cut—that is, a cut other than the round brilliant—which the particular crystal shape lends itself to. The original round brilliant-cut was developed by Marcel Tolkowsky in 1919, in recent decades, most girdles are faceted. Many girdles have 32,64,80, or 96 facets, while the facet count is standard, the actual proportions are not universally agreed upon. One may speak of the American cut or the Scandinavian standard, to give, today, Tolkowskys ideal model has been overused. The original model was a guideline, as there were several aspects of diamond-cutting that were not explored or accounted for in that model. Figures 1 and 2 show the facets of a round brilliant diamond, Figure 1 assumes that the thick part of the girdle is the same thickness at all 16 thick parts. It does not consider the effects of indexed upper girdle facets, Figure 2 is adapted from Figure 37 of Marcel Tolkowskys Diamond Design, which was originally published in 1919. Since 1919, the lower girdle facets have become longer, as a result, the pavilion main facets have become narrower. The relationship between the angle and the pavilion angle has the greatest effect on the look of the diamond. A slightly steep pavilion angle can be complemented by a shallower crown angle, other proportions also affect the look of the diamond, The table ratio is highly significant. The length of the lower girdle facets affects whether Hearts and arrows can be seen in the stone, most round brilliant diamonds have roughly the same girdle thickness at all 16 thick parts. So-called cheated girdles have thicker girdles where the main facets touch the girdle than where adjacent upper girdle facets touch the girdle and these stones weigh more, and have worse optical performance. So-called painted girdles have thinner girdles where the main facets touch the girdle than where adjacent upper girdle facets touch the girdle and these stones have less light leakage at the edge of the stone. Some diamonds with painted girdles receive lower grades in the GIAs cut grading system, several groups have developed diamond cut grading standards. They all disagree somewhat on which proportions make the best cut, there are certain proportions that are considered best by two or more groups however. The AGA standards may be the strictest, david Atlas has suggested that they are overly strict
6.
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
7.
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
8.
Culet
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In gemology, a culet is a flat face on the bottom of a gemstone. During the 14th century, after the adoption of the table cut, the term used for these bottom facets derives from the Latin word for bottom, culus. The culet is added largely to protect the integrity of the gemstone, on a diamond, the cleavage plane runs parallel to the octahedral faces, and so any damage to the tip of the diamond could cause a split up the entire length of the pavilion. With other gemstones that are not subject to cleavage, the culet is added to protect the fragility of the pointed tip. The culet has remained optional on many diamond cuts up to the present day, nonetheless, culet facets are common on modern brilliant-cut diamonds. History of Lapidary Gemstone Cutting History
9.
Spodumene
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Spodumene is a pyroxene mineral consisting of lithium aluminium inosilicate, LiAl2, and is a source of lithium. It occurs as colorless to yellowish, purplish, or lilac kunzite, yellowish-green or emerald-green hiddenite, prismatic crystals, single crystals of 14.3 m in size are reported from the Black Hills of South Dakota, United States. The normal low-temperature form α-spodumene is in the system whereas the high-temperature β-spodumene crystallizes in the tetragonal system. The normal α-spodumene converts to β-spodumene at temperatures above 900 °C, crystals are typically heavily striated parallel to the principal axis. Crystal faces are often etched and pitted with triangular markings, spodumene was first described in 1800 for an occurrence in the type locality in Utö, Södermanland, Sweden. It was discovered by Brazilian naturalist Jose Bonifacio de Andrada e Silva, the name is derived from the Greek spodumenos, meaning burnt to ashes, owing to the opaque, ash-grey appearance of material refined for use in industry. Spodumene occurs in granite pegmatites and aplites. Associated minerals include, quartz, albite, petalite, eucryptite, lepidolite, transparent material has long been used as a gemstone with varieties kunzite and hiddenite noted for their strong pleochroism. Source localities include Afghanistan, Australia, Brazil, Madagascar, Pakistan, Québec in Canada and North Carolina, spodumene is an important source of lithium for use in ceramics, mobile phone and automotive batteries, medicine, Pyroceram and as a fluxing agent. Lithium is extracted from spodumene by fusing in acid, world production of lithium via spodumene is around 80,000 metric tonnes per annum, primarily from the Greenbushes pegmatite of Western Australia and from some Chinese and Chilean sources. The Talison mine in Greenbushes, Western Australia has a reserve of 13 million tonnes. Some think that spodumene will become a important source of lithium due to the emergence of alkaline brine lake sources in Chile, China and Argentina. Lithium chloride is converted to lithium carbonate and lithium hydroxide by reaction with sodium carbonate, however, pegmatite-based projects benefit from being quicker to move into production than brines, which can take 18 months to 3 years, depending on evaporation rates. With pegmatites, once a mill is built, the production of lithium carbonate takes only a matter of days, another key advantage that spodumene has over its more popular brine rivals is the purity of the lithium carbonate it can produce. Hiddenite is an emerald green gem variety first reported from Alexander County, North Carolina. It was named in honor of William Earl Hidden, mining engineer, mineral collector and this emerald green variety of spodumene is colored by chromium, just like emeralds. Not all green spodumene is colored with chromium, which tend to have a lighter color, kunzite is a pink to lilac colored gemstone, a variety of spodumene with the color coming from minor to trace amounts of manganese. Some kunzite used for gemstones has been heated to enhance its color and it is also frequently irradiated to enhance the color
10.
Faceting machine
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A faceting machine is broadly defined as any device that allows the user to place and polish facets onto a mineral specimen. Machines can range in sophistication from primitive jamb-peg machines to highly refined, a major division among machines is found between those that facet diamonds and those that do not. Specialized equipment is required for diamond faceting, and faceting as an occupation rarely bridges the gap between diamond and non-diamond workmanship, a second division can be made between industrial faceting and custom/hobby faceting. The vast majority of jewelry-store gemstones are faceted either abroad in factories or entirely by machines, a number of manufacturers sell non-commercial faceting machines. Among the more common names are Ultra-Tec, Facetron, Graves and Poly-Metric and they range in price from just over $1,000 to upwards of $4,000. The essentials of how a machine works will be explored through this type of machine. There are two components of a faceting machine, The mast/head assembly, and the grinding wheel. The mast assembly is the heart of the faceting machine, the rest of the machine is simple in construction, including the arbor for the grinding wheel, the motor that runs the arbor, a drip tank, and the controlling switches. These are described below, Arbor, Similar to the prong in the middle of a record player, the lap, or grinding wheel, is placed onto it rather than a record, and the arbor is machined to run perfectly flat when turning. Arbor Nut, The screw that fits through the top of the lap, motor, Typically the motor is housed beneath the machine and is attached by one of several means to the arbor. Motors are always velocity-variable and some can be reversed, i. e. clockwise as well as counterclockwise, drip Tank, The drip tank serves two purposes. 1) The friction produced from contact between the rough and the lap creates heat, which can damage the lap and create stress fractures in the stone. The drip tank allows the user to choose a drip rate via spigot and to position the spigot over the lap, 2) The dust produced from grinding minerals can cause pulmonary disease if inhaled. The flow of water captures the particles in a slurry, which drains into a container around. This container has a tube that drains into a second receptacle. Controls, The controls are simple and control the rotational velocity of the lap—the key control—and sometimes the direction of spin. As stated above, the mast assembly is what makes a machine a faceting machine. Its components are as follows, Mast, A vertical pole mounted into the base of the machine on which the assembly is positioned, the pole must be machined with extreme care to ensure its perpendicularity to the lap
11.
Transparency and translucency
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In the field of optics, transparency is the physical property of allowing light to pass through the material without being scattered. On a macroscopic scale, the photons can be said to follow Snells Law, in other words, a translucent medium allows the transport of light while a transparent medium not only allows the transport of light but allows for image formation. The opposite property of translucency is opacity, transparent materials appear clear, with the overall appearance of one color, or any combination leading up to a brilliant spectrum of every color. When light encounters a material, it can interact with it in different ways. These interactions depend on the wavelength of the light and the nature of the material, photons interact with an object by some combination of reflection, absorption and transmission. Some materials, such as glass and clean water, transmit much of the light that falls on them and reflect little of it. Many liquids and aqueous solutions are highly transparent, absence of structural defects and molecular structure of most liquids are mostly responsible for excellent optical transmission. Materials which do not transmit light are called opaque, many such substances have a chemical composition which includes what are referred to as absorption centers. Many substances are selective in their absorption of light frequencies. They absorb certain portions of the spectrum while reflecting others. The frequencies of the spectrum which are not absorbed are either reflected or transmitted for our physical observation and this is what gives rise to color. The attenuation of light of all frequencies and wavelengths is due to the mechanisms of absorption. Transparency can provide almost perfect camouflage for animals able to achieve it and this is easier in dimly-lit or turbid seawater than in good illumination. Many marine animals such as jellyfish are highly transparent, at the atomic or molecular level, physical absorption in the infrared portion of the spectrum depends on the frequencies of atomic or molecular vibrations or chemical bonds, and on selection rules. Nitrogen and oxygen are not greenhouse gases because there is no absorption because there is no molecular dipole moment. With regard to the scattering of light, the most critical factor is the scale of any or all of these structural features relative to the wavelength of the light being scattered. Primary material considerations include, Crystalline structure, whether or not the atoms or molecules exhibit the long-range order evidenced in crystalline solids, glassy structure, scattering centers include fluctuations in density or composition. Microstructure, scattering centers include internal surfaces such as boundaries, crystallographic defects
12.
Lustre (mineralogy)
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Lustre or luster is the way light interacts with the surface of a crystal, rock, or mineral. The word traces its origins back to the latin lux, meaning light, a range of terms are used to describe lustre, such as earthy, metallic, greasy, and silky. Similarly, the term refers to a glassy lustre. A list of terms is given below. Lustre varies over a continuum, and so there are no rigid boundaries between the different types of lustre. The terms are frequently combined to describe types of lustre. Some minerals exhibit unusual optical phenomena, such as asterism or chatoyancy, a list of such phenomena is given below. Adamantine minerals possess a superlative lustre, which is most notably seen in diamond, such minerals are transparent or translucent, and have a high refractive index. Minerals with an adamantine lustre are uncommon, with examples being cerussite. Minerals with a degree of lustre are referred to as subadamantine, with some examples being garnet. Dull minerals exhibit little to no lustre, due to coarse granulations which scatter light in all directions, a distinction is sometimes drawn between dull minerals and earthy minerals, with the latter being coarser, and having even less lustre. Greasy minerals resemble fat or grease, a greasy lustre often occurs in minerals containing a great abundance of microscopic inclusions, with examples including opal and cordierite. Many minerals with a greasy lustre also feel greasy to the touch, metallic minerals have the lustre of polished metal, and with ideal surfaces will work as a reflective surface. Examples include galena, pyrite and magnetite, pearly minerals consist of thin transparent co-planar sheets. Light reflecting from these layers give them a lustre reminiscent of pearls, such minerals possess perfect cleavage, with examples including muscovite and stilbite. Resinous minerals have the appearance of resin, chewing gum or plastic, a principal example is amber, which is a form of fossilized resin. Silky minerals have an arrangement of extremely fine fibres, giving them a lustre reminiscent of silk. Examples include asbestos, ulexite and the satin spar variety of gypsum, a fibrous lustre is similar, but has a coarser texture
13.
Pleonaste
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Ceylonite and pleonaste are dingy blue or grey to black varieties of spinel. Ceylonite, named for the island of Ceylon, is a ferroan spinel with Mg, Fe from 3,1 and 1,1, and little or no ferric iron. Pleonaste is named from the Greek for abundant, for its many crystal forms and it is sometimes used as a gemstone. The mineral ceylonite has the composition of Al2O4, putting it into a group of minerals known as the spinels. The oxide spinels have a formula of the model 2O4, where is commonly Fe2+, Mg2+, or Mn2+, ceylonite has the structural formula Al2O4, where cation is Mg2+ or Fe2+. This formula creates a face centered cubic Bravais lattice, with a group of Fd3m. The point symmetry can be three possibilities, 4*3m, 3*m, or mm, within the oxygen sub-lattice of ceylonite, the Mg2+ ions occupy tetrahedral 4c symmetry positions, and the Al3+ ions occupy octahedral 8f site. This allows for the remaining octahedral site to be open for defects, causing a variety in structure, ceylonite can actually undergo a solid solution series in which the composition changes, but it is still ceylonite. Magnesium rich ceylonite can undergo an increase in iron that will replace the magnesium cation in the A-block, the chemistry changes, but the mineral technically remains ceylonite. The ceylonite first discovered on the island of Ceylon, modern day Sri Lanka, was found imbedded in calcareous spar, the crystals were located in a low lying dried up river, and were relatively shallow in the soil,8 to 10 inches. On one side of the bank a mass of gneiss was exposed, on the other, the grains in the first discovered ceylonite looked of compacted soils, leading one to believe they were perhaps sedimentary in formation. This was a hypothesis, and did not hold true after further analysis. The Mg-ceylonite has a more reliable study of its geological occurrence. It is found in Mg and Al rich igneous rocks, as well as, like many rocks and mineral, ceylonite is weathered and can be found in sedimentary rocks. Ceylonite and pleonaste are historical terms in mineralogy, nevertheless, both terms are used in the current mineralogical literature. Grimes, R. W. Bacorisen, D. Smith, R. Uberuaga, June 2008, Defect processes in MgAl2O4 spinel, Solid State Sciences,10,6, 717-724. Ramprasad, T.30 June 2006, Seafloor spreading magnetic anomalies south off Sri Lanka, Marine Geology,229,34, king, R. J. Minerals explained 40, The spinels. Sickafus, K. E. Wills, J. M. and Grimes, journal of the American Ceramic Society
14.
Spinel
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Spinel is the magnesium aluminium member of the larger spinel group of minerals. It has the formula MgAl2O4 in the crystal system. Its name comes from Latin spina, balas ruby is an old name for a rose-tinted variety of spinel. Spinel crystallizes in the system, common crystal forms are octahedra. It has an imperfect cleavage and a conchoidal fracture. Its hardness is 8, its gravity is 3. 5–4.1. It may be colorless, but is usually shades of red, blue, green, yellow, brown, black. There is a natural white spinel, now lost, that surfaced briefly in what is now Sri Lanka. The Samarian Spinel is the largest known spinel in the world, the transparent red spinels were called spinel-rubies or balas rubies. In the past, before the arrival of modern science, spinels, after the 18th century the word ruby was only used for the red gem variety of the mineral corundum and the word spinel came to be used. Balas is derived from Balascia, the ancient name for Badakhshan, mines in the Gorno Badakhshan region of Tajikistan was for centuries the main source for red and pink spinels. Spinel has long been found in the gravel of Sri Lanka and in limestones of the Badakshan Province in modern-day Afghanistan and Tajikistan. Recently gem quality spinels also found in the marbles of Luc Yen, Mahenge and Matombo, Tsavo and in the gravels of Tunduru and this is why spinel and ruby are often found together. Spinel, 2O4, is common in peridotite in the uppermost Earths mantle, Spinel, Al2O4, is a common mineral in the Ca-Al-rich inclusions in some chondritic meteorites. Synthetic spinel, accidentally produced in the middle of the 18th century, has described more recently in scientific publications in 2000 and 2004. By 2015, transparent spinel was being made in sheets and other shapes through sintering, synthetic spinel which looks like glass but has notably higher strength against pressure, can also have applications in military and commercial use. Spinel group Ceylonite The Samarian Spinel, the largest known spinel in the world, part of the Iranian Crown Jewels Black Princes Ruby Deer, Howie, an Introduction to the Rock-Forming Minerals, Longman, pp. 424–433, ISBN 0-582-44210-9. Gemstones of the World 3rd edition, Sterling, pp. 116–117, Spinel structure at the University of Wisconsin - Green Bay Spinel structure at the Institut for materials science of the University of Kiel Value of Spinel
15.
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
16.
Total internal reflection
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Total internal reflection is the phenomenon which occurs when a propagated wave strikes a medium boundary at an angle larger than a particular critical angle with respect to the normal to the surface. If the refractive index is lower on the side of the boundary and the incident angle is greater than the critical angle. The critical angle is the angle of incidence above which the internal reflection occurs. This is particularly common as a phenomenon, where light waves are involved. When a wave reaches a boundary between different materials with different refractive indices, the wave will in general be partially refracted at the boundary surface, and partially reflected. This can only occur when the wave in a medium with a refractive index reaches a boundary with a medium of lower refractive index. For example, it will occur with light reaching air from glass, Total internal reflection of light can be demonstrated using a semi-circular block of glass or plastic. A ray box shines a beam of light onto the glass medium. At the glass/air boundary of the surface, what happens will depend on the angle. If θc is the angle, then the following scenarios depict what will happen according to the size of the incident angle. If θ ≤ θc, the ray will split, some of the ray will reflect off the boundary and this is not total internal reflection. If θ > θc, the ray reflects from the boundary. This is called total internal reflection and this physical property makes optical fibers useful and prismatic binoculars possible. It is also what gives diamonds their distinctive sparkle, as diamond has a high refractive index. The critical angle is the angle of incidence for which the angle of refraction is 90°, the angle of incidence is measured with respect to the normal at the refractive boundary. Consider a light ray passing from glass into air, the light emanating from the interface is bent towards the glass. When the incident angle is increased sufficiently, the transmitted angle reaches 90 degrees and it is at this point no light is transmitted into air. The critical angle θ c is given by Snells law, n 1 sin θ i = n 2 sin θ t, rearranging Snells Law, we get incidence sin θ i = n 2 n 1 sin θ t
17.
Lapping
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Lapping is a machining process, in which two surfaces are rubbed together with an abrasive between them, by hand movement or using a machine. This produces microscopic conchoidal fractures as the abrasive rolls about between the two surfaces and removes material from both, the other form of lapping involves a softer material such as pitch or a ceramic for the lap, which is charged with the abrasive. The lap is then used to cut a harder material — the workpiece, the abrasive embeds within the softer material, which holds it and permits it to score across and cut the harder material. Taken to a limit, this will produce a polished surface such as with a polishing cloth on an automobile. This is one twentieth of the wavelength of light from the commonly used 632.8 nm helium neon laser light source, surfaces this flat can be molecularly bonded by bringing them together under the right conditions. By way of example, a piece of lead may be used as the lap, charged with emery, the small plate shown in the first picture is a hand lapping plate. That particular plate is made of cast iron, in use, a slurry of emery powder would be spread on the plate and the workpiece simply rubbed against the plate, usually in a figure-eight pattern. The second picture is of a commercially available lapping machine, the lap or lapping plate in this machine is 30 centimetres in diameter, about the smallest size available commercially. At the other end of the spectrum, machines with 8-to-10-foot-diameter plates are not uncommon. Referring to the picture again, the lap is the large circular disk on the top of the machine. On top of the lap are two rings, the workpiece would be placed inside one of these rings. A weight would then be placed on top of the workpiece, the weights can also be seen in the picture along with two fiber spacer disks that are used to even the load. In operation, the stay in one location as the lapping plate rotates beneath them. In this machine, a slurry pump can be seen at the side. When there is a requirement to lap very small specimens, a jig can be used to hold the material while it is lapped. A jig allows precise control of the orientation of the specimen to the lapping plate, due to the dimensions of such small samples, traditional loads and weights are too heavy as they would destroy delicate materials. The jig sits in a cradle on top of the lapping plate, where the mating of the two surfaces is more important than the flatness, the two pieces can be lapped together. This yields closeness-of-fit results comparable to that of two pieces, without quite the same degree of testing required for the latter
18.
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
19.
Diamond blade
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A diamond blade is a saw blade which has diamonds fixed on its edge for cutting hard or abrasive materials. Diamond blades are available in different shapes, Circular diamond saw blades are the most widely used type of diamond blade, a diamond gang saw blade is a long steel plate with diamond segments welded onto it. Normally, tens or hundreds of diamond saw blades are used together to saw raw stone blocks. A diamond band saw blade is a closed steel band with diamonds fixed on one edge of the band. Diamond blades designed for specific uses include marble, granite, concrete, asphalt, masonry, general purpose blades are also available. Vacuum brazed diamond saws are manufactured by welding synthetic diamond particles to the edge of the circular saw blade in a vacuum brazing furnace. All of the particles are on the exterior cutting edge of the blade. Finer synthetic diamond grits will reduce the chipping of tile and burring of steel, larger diamond grits will provide a higher cutting speed, but will be more likely to cause chipping, burring, or cracking. Fire departments require blades to be made with a large diamond grit. An intermediate grit size is used by the production industry, sintered metal-bonded diamond blades are the most common type of blade. These blades consist of a core and diamond segments, which are made by combining synthetic diamond crystals with metal powder. The diamond segments are also known as the teeth of the blade. The steel core can vary in design, some cores have spaces between segments to provide cooling and slurry removal, while others have a single continuous rim for smoother cutting. The type of core that can be used depends on the type of materials that the blade is designed to cut. A wholly sintered diamond blade is made by putting the core, together with the diamonds. Consequently, the diameter of wholly sintered diamond blades is not very large, because it is participating in the sintering process, the steel core cannot be quenched, so the hardness and strength of the core are not very high. This means that these types of diamond blade may deform in high-load and high-intensity cutting processes, silver brazed and laser welded diamond blades do not have this weakness because their diamond segments and steel core are treated separately. Silver brazed diamond blades diamond segments are brazed to the core using a silver solder
20.
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
21.
Crystal structure
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In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material. Ordered structures occur from the nature of the constituent particles to form symmetric patterns that repeat along the principal directions of three-dimensional space in matter. The smallest group of particles in the material that constitutes the pattern is the unit cell of the structure. The unit cell completely defines the symmetry and structure of the crystal lattice. The repeating patterns are said to be located at the points of the Bravais lattice, the lengths of the principal axes, or edges, of the unit cell and the angles between them are the lattice constants, also called lattice parameters. The symmetry properties of the crystal are described by the concept of space groups, all possible symmetric arrangements of particles in three-dimensional space may be described by the 230 space groups. The crystal structure and symmetry play a role in determining many physical properties, such as cleavage, electronic band structure. The crystal structure of a material can be described in terms of its unit cell, the unit cell is a box containing one or more atoms arranged in three dimensions. The unit cells stacked in three-dimensional space describe the arrangement of atoms of the crystal. Commonly, atomic positions are represented in terms of fractional coordinates, the atom positions within the unit cell can be calculated through application of symmetry operations to the asymmetric unit. The asymmetric unit refers to the smallest possible occupation of space within the unit cell and this does not, however imply that the entirety of the asymmetric unit must lie within the boundaries of the unit cell. Symmetric transformations of atom positions are calculated from the group of the crystal structure. Vectors and planes in a lattice are described by the three-value Miller index notation. It uses the indices ℓ, m, and n as directional parameters, which are separated by 90°, by definition, the syntax denotes a plane that intercepts the three points a1/ℓ, a2/m, and a3/n, or some multiple thereof. That is, the Miller indices are proportional to the inverses of the intercepts of the plane with the unit cell, if one or more of the indices is zero, it means that the planes do not intersect that axis. A plane containing a coordinate axis is translated so that it no longer contains that axis before its Miller indices are determined, the Miller indices for a plane are integers with no common factors. Negative indices are indicated with horizontal bars, as in, in an orthogonal coordinate system for a cubic cell, the Miller indices of a plane are the Cartesian components of a vector normal to the plane. Likewise, the planes are geometric planes linking nodes
22.
Surface energy
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Surface energy, or interface energy, quantifies the disruption of intermolecular bonds that occur when a surface is created. The surface energy may therefore be defined as the energy at the surface of a material compared to the bulk. Another way to view the energy is to relate it to the work required to cut a bulk sample. Cutting a solid body into pieces disrupts its bonds, and therefore consumes energy, if the cutting is done reversibly, then conservation of energy means that the energy consumed by the cutting process will be equal to the energy inherent in the two new surfaces created. The unit surface energy of a material would therefore be half of its energy of cohesion, all things being equal, in practice. Surfaces often change their form away from the cleaved bond model just implied above. They are found to be highly dynamic regions, which readily rearrange or react, measuring the surface energy of a solid The surface energy of a liquid may be measured by stretching a liquid membrane. In that case, in order to increase the area of a mass of liquid by an amount, δA. However, such a method cannot be used to measure the energy of a solid because stretching of a solid membrane induces elastic energy in the bulk in addition to increasing the surface energy. The surface energy of a solid is measured at high temperatures. At such temperatures the solid creeps and even though the area changes. V = π r 2 l = constant ⟹ δ V =2 π r l δ r + π r 2 δ l =0 ⟹ δ r = − r 2 l δ l. Therefore, the energy density can be expressed as γ = P l π r. The surface energy density of the solid can be computed by measuring P, r and this method is valid only if the solid is isotropic, meaning the surface energy is the same for all crystallographic orientations. While this is strictly true for amorphous solids and liquids. In particular, if the sample is polygranular or made by powder sintering this is a good approximation, in the case of single-crystal materials, such as natural gemstones, anisotropy in the surface energy leads to faceting. The shape of the crystal is related to the energy by the Wulff construction. The surface energy of the facets can thus be found to within a constant by measuring the relative sizes of the facets
23.
Bravais lattice
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This discrete set of vectors must be closed under vector addition and subtraction. For any choice of position vector R, the lattice looks exactly the same, when the discrete points are atoms, ions, or polymer strings of solid matter, the Bravais lattice concept is used to formally define a crystalline arrangement and its frontiers. A crystal is made up of an arrangement of one or more atoms repeated at each lattice point. Consequently, the crystal looks the same when viewed from any equivalent lattice point, two Bravais lattices are often considered equivalent if they have isomorphic symmetry groups. In this sense, there are 14 possible Bravais lattices in three-dimensional space, the 14 possible symmetry groups of Bravais lattices are 14 of the 230 space groups. In two-dimensional space, there are 5 Bravais lattices, grouped into four crystal families, the unit cells are specified according to the relative lengths of the cell edges and the angle between them. The area of the cell can be calculated by evaluating the norm || a × b ||. The properties of the families are given below, In three-dimensional space. These are obtained by combining one of the six families with one of the centering types. For example, the monoclinic I lattice can be described by a monoclinic C lattice by different choice of crystal axes, similarly, all A- or B-centred lattices can be described either by a C- or P-centering. This reduces the number of combinations to 14 conventional Bravais lattices, the unit cells are specified according to the relative lengths of the cell edges and the angles between them. The volume of the cell can be calculated by evaluating the triple product a ·, where a, b. The properties of the families are given below, In four dimensions. Of these,23 are primitive and 41 are centered, ten Bravais lattices split into enantiomorphic pairs. Bravais, A. Mémoire sur les systèmes formés par les points distribués régulièrement sur un plan ou dans lespace, hahn, Theo, ed. International Tables for Crystallography, Volume A, Space Group Symmetry. Catalogue of Lattices Smith, Walter Fox
24.
Thermodynamic free energy
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The thermodynamic free energy is the amount of work that a thermodynamic system can perform. The concept is useful in the thermodynamics of chemical or thermal processes in engineering, the free energy is the internal energy of a system minus the amount of energy that cannot be used to perform work. This unusable energy is given by the entropy of a multiplied by the temperature of the system. Like the internal energy, the energy is a thermodynamic state function. Energy is a generalization of free energy, since energy is the ability to do work which is free energy, free energy is that portion of any first-law energy that is available to perform thermodynamic work, i. e. work mediated by thermal energy. Free energy is subject to loss in the course of such work. Since first-law energy is conserved, it is evident that free energy is an expendable. Several free energy functions may be formulated based on system criteria, free energy functions are Legendre transformations of the internal energy. The Helmholtz free energy has a theoretical importance since it is proportional to the logarithm of the partition function for the canonical ensemble in statistical mechanics. The historically earlier Helmholtz free energy is defined as A = U − TS, where U is the energy, T is the absolute temperature. Its change is equal to the amount of work done on, or obtainable from. Thus its appellation work content, and the designation A from Arbeit, the Gibbs free energy is given by G = H − TS, where H is the enthalpy. Historically, these terms have been used inconsistently. In physics, free energy most often refers to the Helmholtz free energy, denoted by A, while in chemistry, since both fields use both functions, a compromise has been suggested, using A to denote the Helmholtz function and G for the Gibbs function. While A is preferred by IUPAC, G is sometimes still in use, the use of the words “latent heat” implied a similarity to latent heat in the more usual sense, it was regarded as chemically bound to the molecules of the body. In the adiabatic compression of a gas, the heat remained constant. During the early 19th century, the concept of perceptible or free caloric began to be referred to as “free heat” or heat set free. In 1824, for example, the French physicist Sadi Carnot, in his famous “Reflections on the Motive Power of Fire”, an increasing number of books and journal articles do not include the attachment “free”, referring to G as simply Gibbs energy
25.
Crystal growth
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A crystal is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. Crystal growth is a stage of a crystallization process, and consists in the addition of new atoms, ions. The growth typically follows a stage of either homogeneous or heterogeneous nucleation, unless a seed crystal. The action of crystal growth yields a crystalline solid whose atoms or molecules are close packed. The crystalline state of matter is characterized by a distinct structural rigidity, most crystalline solids have high values both of Youngs modulus and of the shear modulus of elasticity. This contrasts with most liquids or fluids, which have a low shear modulus, crystalline solids are typically formed by cooling and solidification from the liquid state. According to the Ehrenfest classification of first-order phase transitions, there is a change in volume at the melting point. Within this context, the crystal and melt are distinct phases with an interfacial discontinuity having a surface of tension with a surface energy. Thus, a metastable parent phase is stable with respect to the nucleation of small embryos or droplets from a daughter phase. Such first-order transitions must proceed by the advancement of a region whose structure. The process of nucleation and growth generally occurs in two different stages, in the first nucleation stage, a small nucleus containing the newly forming crystal is created. Nucleation occurs relatively slowly as the initial components must impinge on each other in the correct orientation and placement for them to adhere. After crystal nucleation, the stage of growth rapidly ensues. Crystal growth spreads outwards from the nucleating site, in this faster process, the elements which form the motif add to the growing crystal in a prearranged system, the crystal lattice, started in crystal nucleation. As first pointed out by Frank, perfect crystals would only grow exceedingly slowly, the conditions of a homogeneous environment are often approximated to but rarely ever realized. Crystal growth always involves some form of transport of matter or heat, and homogeneous conditions for the transport process can only exist for spherical, cylindrical, or infinite plane surfaces. A polyhedral crystal cannot grow with uniform levels of supersaturation over its faces, in general, the supersaturation is greatest at its corners. This refutes the assumption that the rate is a function of orientation
26.
Stealth technology
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It corresponds to military camouflage for these parts of the electromagnetic spectrum. Designers turned to develop a particular shape for planes that tended to reduce detection, radar-absorbent material was also tested and made to reduce or block radar signals that reflect off from the surface of planes. Such changes to shape and surface composition form stealth technology as used on the Northrop Grumman B-2 Spirit Stealth Bomber. The concept of stealth is to operate or hide without giving enemy forces any indications as to the presence of friendly forces and this concept was first explored through camouflage by blending into the background visual clutter. Some military uniforms are treated with chemicals to reduce their infrared signature, a modern stealth vehicle is designed from the outset to have a chosen spectral signature. The degree of stealth embodied in a design is chosen according to the predicted capabilities of projected threats. The concept of camouflage is known to predate warfare itself, hunters have been using vegetation to conceal themselves perhaps as long as people have been hunting. In England, irregular units of gamekeepers in the 17th century were the first to adopt drab colours as a form of camouflage, following examples from the continent. During World War I, the Germans experimented with the use of Cellon, single examples of the Fokker E. III Eindecker fighter monoplane, the Albatros C. I two-seat observation biplane, and the Linke-Hofmann R. I prototype heavy bomber were covered with Cellon. In fact, sunlight glinting from the material made the even more visible. Celon was also found to be quickly degraded both by sunlight and in-flight temperature changes so the attempt to make transparent aircraft was not proceeded with, in 1916, the British modified a small SS class airship for the purpose of night-time reconnaissance over German lines on the Western Front. Diffused lighting camouflage, a form of counter-illumination camouflage, was trialled by the Royal Canadian Navy from 1941 to 1943. The concept was followed up, but for aircraft, by the Americans and this ability was rendered obsolete by radar. The U-boat U-480 may have been the first stealth submarine and it featured an anechoic tile rubber coating, one layer of which contained circular air pockets to defeat ASDIC sonar. Radar absorbent rubber/semiconductor composite paints and materials were used by the Kriegsmarine on submarines in World War II, tests showed they were effective in reducing radar signatures at both short and long wavelengths. In 1960, the first stealth technology development program was initiated by USAF and this was achieved through specially designed screens over the air intake, radar-absorbent material on the fuselage and a special radar-absorbing paint. Central Intelligence Agency requested funding for an aircraft to replace the existing U-2 spy planes. Radar absorbent material was used on U-2 spy planes, and various plane shapes designed to reduce radar detection were developed in earlier prototypes, in 1964, an optimal plane shape taking into account compactness was developed for another Blackbird, the Lockheed SR-71
27.
Lockheed F-117 Nighthawk
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The Lockheed F-117 Nighthawk is a single-seat, twin-engine stealth attack aircraft that was developed by Lockheeds secretive Skunk Works division and operated by the United States Air Force. The F-117 was based on the Have Blue technology demonstrator, and was the first operational aircraft to be designed around stealth technology, the maiden flight of the Nighthawk took place in 1981, and the aircraft achieved initial operating capability status in 1983. The Nighthawk was shrouded in secrecy until it was revealed to the public in 1988, the F-117 was widely publicized for its role in the Persian Gulf War of 1991. Although it was referred to as the Stealth Fighter, it was strictly an attack aircraft. F-117s took part in the conflict in Yugoslavia, where one was shot down by a missile on 27 March 1999. The U. S. Air Force retired the F-117 on 22 April 2008, sixty-four F-117s were built,59 of which were production versions, with the other five being demonstrators/prototypes. Ufimtsev was extending theoretical work published by the German physicist Arnold Sommerfeld, ufimtsev demonstrated that he could calculate the radar cross-section across a wings surface and along its edge. The obvious and logical conclusion was that even an aircraft could be made difficult to see by radar by exploiting this principle. By the 1970s, when Lockheed analyst Denys Overholser found Ufimtsevs paper, computers and software had advanced significantly, the F-117 was born after combat experience in the Vietnam War when increasingly sophisticated Soviet surface-to-air missiles downed heavy bombers. It was a project, an ultra-secret program for much of its life, very few people in the Pentagon knew the program even existed. The project began in 1975 with a called the Hopeless Diamond. The following year, the Defense Advanced Research Projects Agency issued Lockheed Skunk Works a contract to build and these subscale aircraft incorporated jet engines of the Northrop T-38A, fly-by-wire systems of the F-16, landing gear of the A-10, and environmental systems of the C-130. By bringing together existing technology and components, Lockheed built two demonstrators under budget, at $35 million for aircraft, and in record time. The maiden flight of the demonstrators occurred on 1 December 1977, although both aircraft were lost during the demonstration program, test data proved positive. The success of Have Blue led the government to increase funding for stealth technology, much of that increase was allocated towards the production of an operational stealth aircraft, the Lockheed F-117A, under the program code name Senior Trend. The decision to produce the F-117A was made on 1 November 1978, the program was led by Ben Rich, with Alan Brown as manager of the project. Rich called on Bill Schroeder, a Lockheed mathematician, and Denys Overholser, the first YF-117A, serial number 79-0780, made its maiden flight from Groom Lake, Nevada, on 18 June 1981, only 31 months after the full-scale development decision. The first production F-117A was delivered in 1982, and operational capability was achieved in October 1983, after the announcement pilots could fly the F-117 during daytime and no longer needed to be associated with the A-7, flying the T-38 supersonic trainer for travel and training instead
28.
Princess cut
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The princess cut is the second most popular cut shape for diamonds, next to a round brilliant. The face-up shape of the cut is square or rectangular. The princess cut is a new diamond cut, having been created in the 1960s. A princess cut with the width as the diameter of a round brilliant will weigh more as it has four corners which would otherwise have been cut off. The princess cut is referred to as a square modified brilliant. However, while displaying a good degree of brilliance, its style is unique. The Barion shaped cut has now renamed the Princess cut. The ability to retain more crystal weight makes this shape popular amongst diamond cutters, accredited Gem Appraisers and American Gem Society Laboratory and European Gem Laboratories-USA are currently the only labs that grade the Princess cut for cut. Measurements vary for a cut diamond and many diamond manufacturers market ideal diamonds with differing facet patterns. The name princess cut was used in connection with another diamond cut, otherwise known as the profile cut, designed by Arpad Nagy. The same name was used and made popular by Ygal Perlman, Betzalel Ambar. A similar cut with only 49 facets, as opposed to the original 58 facets of the cut, was later branded the Quadrillion. Three years of research yielded a square stone with faceting similar to that of a round brilliant cut diamond. The number of chevrons can affect the overall outlook of a cut diamond. This can usually be determined by the diagram that is plotted in diamond grading reports. By adding more chevrons on the side of the diamond. As a result, it can give a cut diamond a crushed ice look. Vice versa, when a cut diamond has fewer chevrons
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