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.
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
5.
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
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.
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
8.
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
9.
Jadeite
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Jadeite is a pyroxene mineral with composition NaAlSi2O6. It has a Mohs hardness of about 6.5 to 7.0 depending on the composition, the mineral is dense, with a specific gravity of about 3.4. The name jadeite is derived from the Spanish phrase piedra de ijada which means stone of the side and it was believed to cure kidney stones if it was rubbed against the side of the afflicted persons body. The Latin version of the name, lapis nephriticus, is the origin of the term nephrite, Jadeite forms solid solutions with other pyroxene endmembers such as augite and diopside, aegirine, and kosmochlor. Pyroxenes rich in both the jadeite and augite endmembers are known as omphacite, Jadeite is formed in metamorphic rocks under high pressure and relatively low temperature conditions. Albite is a mineral of the Earths crust, and it has a specific gravity of about 2.6. With increasing pressure, albite breaks down to form the high-pressure assemblage of jadeite plus quartz, minerals associated with jadeite include, glaucophane, lawsonite, muscovite, aragonite, serpentine and quartz. Rocks that consist almost entirely of jadeite are called jadeitite, in all well-documented occurrences, jadeitite appears to have formed from subduction zone fluids in association with serpentinite. Jadeitite is resistant to weathering, and boulders of jadeitite released from the environments in which they formed are found in a variety of environments. Jadeites color commonly ranges from white through pale apple green to deep green but can also be blue-green, pink, lavender. Chloromelanite is a dark green to black variety. Color is largely affected by the presence of elements such as chromium. Its translucence can be anywhere from entirely solid through opaque to almost clear, variations in color and translucence are often found even within a single specimen. Jadeite is reported from California, US, Myanmar, New Zealand, Guatemala, Itoigawa, Japan, other localities of jadeite include Kazakhstan, Russia, British Columbia, Canada, Italy and Turkestan. Over 180 axe heads made from jadeitite quarried in northern Italy in the Neolithic era have been found across the British Isles, a great many jadeite beads and axe heads as well as the remains of jadeite workshops from the Neolithic era have been uncovered in Itoigawa, Japan. These beads and axes were traded throughout Japan and the Korean Peninsula and were produced by the worlds oldest known jadeite-using culture, Jadeite is one of the minerals recognized as the gemstone jade. Jadeite from the Motagua Valley, Guatemala, was used by the Olmec and Maya peoples, typically, the most highly valued colors of jadeite are the most intensely green, translucent varieties, though traditionally white has been considered the most valuable of the jades by the Chinese. It is thus difficult to obtain and as yet too rare, when purchasing jade, quality is determined by the degree of translucence, cleanness of color and purity of color
10.
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−
11.
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
12.
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
