1.
Albite
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Albite is a plagioclase feldspar mineral. It is the sodium endmember of the solid solution series. As such it represents a plagioclase with less than 10% anorthite content, the pure albite endmember has the formula NaAlSi3O8. Its color is pure white, hence its name from Latin albus. It is a constituent in felsic rocks. Albite crystallizes with triclinic pinacoidal forms and its specific gravity is about 2.62 and it has a Mohs hardness of 6 -6.5. Albite almost always exhibits crystal twinning often as minute parallel striations on the crystal face, Albite often occurs as fine parallel segregations alternating with pink microcline in perthite as a result of exolution on cooling. There are two variants of albite, which are referred to as low albite and high albite, the latter is known as analbite. Although both variants are triclinic, they differ in the volume of their cell, which is slightly larger for the high form. The high form can be produced from the low form by heating above c.750 °C, upon further heating to more than c.1050 °C the crystal symmetry changes from triclinic to monoclinic, this variant is also known as monalbite. It occurs in granitic and pegmatite masses, in hydrothermal vein deposits. It was first reported in 1815 for an occurrence in Finnbo, Falun, Dalarna and it is used as a gemstone. Mineral galleries This article incorporates text from a now in the public domain, Chisholm, Hugh
2.
Basal plane
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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
3.
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
4.
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
5.
Crystal system
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In crystallography, the terms crystal system, crystal family and lattice system each refer to one of several classes of space groups, lattices, point groups or crystals. Informally, two crystals are in the crystal system if they have similar symmetries, though there are many exceptions to this. Space groups and crystals are divided into seven crystal systems according to their point groups, five of the crystal systems are essentially the same as five of the lattice systems, but the hexagonal and trigonal crystal systems differ from the hexagonal and rhombohedral lattice systems. The six crystal families are formed by combining the hexagonal and trigonal crystal systems into one hexagonal family, a lattice system is a class of lattices with the same set of lattice point groups, which are subgroups of the arithmetic crystal classes. The 14 Bravais lattices are grouped into seven lattice systems, triclinic, monoclinic, orthorhombic, tetragonal, rhombohedral, hexagonal, in a crystal system, a set of point groups and their corresponding space groups are assigned to a lattice system. Of the 32 point groups that exist in three dimensions, most are assigned to only one system, in which case both the crystal and lattice systems have the same name. However, five point groups are assigned to two systems, rhombohedral and hexagonal, because both exhibit threefold rotational symmetry. These point groups are assigned to the crystal system. In total there are seven crystal systems, triclinic, monoclinic, orthorhombic, tetragonal, trigonal, hexagonal, a crystal family is determined by lattices and point groups. It is formed by combining crystal systems which have space groups assigned to a lattice system. In three dimensions, the families and systems are identical, except the hexagonal and trigonal crystal systems. In total there are six families, triclinic, monoclinic, orthorhombic, tetragonal, hexagonal. Spaces with less than three dimensions have the number of crystal systems, crystal families and lattice systems. In one-dimensional space, there is one crystal system, in 2D space, there are four crystal systems, oblique, rectangular, square and hexagonal. The relation between three-dimensional crystal families, crystal systems and lattice systems is shown in the table, Note. To avoid confusion of terminology, the term trigonal lattice is not used, if the original structure and inverted structure are identical, then the structure is centrosymmetric. Still, even for non-centrosymmetric case, inverted structure in some cases can be rotated to align with the original structure and this is the case of non-centrosymmetric achiral structure. If the inverted structure cannot be rotated to align with the structure, then the structure is chiral
6.
X-ray crystallography
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By measuring the angles and intensities of these diffracted beams, a crystallographer can produce a three-dimensional picture of the density of electrons within the crystal. From this electron density, the positions of the atoms in the crystal can be determined, as well as their chemical bonds, their disorder. The method also revealed the structure and function of biological molecules, including vitamins, drugs, proteins. X-ray crystallography is still the method for characterizing the atomic structure of new materials. In a single-crystal X-ray diffraction measurement, a crystal is mounted on a goniometer, the goniometer is used to position the crystal at selected orientations. The crystal is illuminated with a finely focused monochromatic beam of X-rays, poor resolution or even errors may result if the crystals are too small, or not uniform enough in their internal makeup. X-ray crystallography is related to other methods for determining atomic structures. Similar diffraction patterns can be produced by scattering electrons or neutrons, for all above mentioned X-ray diffraction methods, the scattering is elastic, the scattered X-rays have the same wavelength as the incoming X-ray. By contrast, inelastic X-ray scattering methods are useful in studying excitations of the sample, Crystals, though long admired for their regularity and symmetry, were not investigated scientifically until the 17th century. Johannes Kepler hypothesized in his work Strena seu de Nive Sexangula that the symmetry of snowflake crystals was due to a regular packing of spherical water particles. The Danish scientist Nicolas Steno pioneered experimental investigations of crystal symmetry, hence, William Hallowes Miller in 1839 was able to give each face a unique label of three small integers, the Miller indices which remain in use today for identifying crystal faces. In the 19th century, a catalog of the possible symmetries of a crystal was worked out by Johan Hessel, Auguste Bravais, Evgraf Fedorov, Arthur Schönflies. Wilhelm Röntgen discovered X-rays in 1895, just as the studies of crystal symmetry were being concluded, physicists were initially uncertain of the nature of X-rays, but soon suspected that they were waves of electromagnetic radiation, in other words, another form of light. Single-slit experiments in the laboratory of Arnold Sommerfeld suggested that X-rays had a wavelength of about 1 angstrom, however, X-rays are composed of photons, and thus are not only waves of electromagnetic radiation but also exhibit particle-like properties. Albert Einstein introduced the concept in 1905, but it was not broadly accepted until 1922. Therefore, these properties of X-rays, such as their ionization of gases. Nevertheless, Braggs view was not broadly accepted and the observation of X-ray diffraction by Max von Laue in 1912 confirmed for most scientists that X-rays were a form of electromagnetic radiation, Crystals are regular arrays of atoms, and X-rays can be considered waves of electromagnetic radiation. Atoms scatter X-ray waves, primarily through the atoms electrons and this phenomenon is known as elastic scattering, and the electron is known as the scatterer
7.
X-ray scattering techniques
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These techniques are based on observing the scattered intensity of an X-ray beam hitting a sample as a function of incident and scattered angle, polarization, and wavelength or energy. However, both scattering and diffraction are related general phenomena and the distinction has not always existed, thus Guiniers classic text from 1963 is titled X-ray diffraction in Crystals, Imperfect Crystals and Amorphous Bodies so diffraction was clearly not restricted to crystals at that time. X-ray reflectivity is a technique for determining thickness, roughness. Wide-angle X-ray scattering, a technique concentrating on scattering angles 2θ larger than 5°, in IXS the energy and angle of inelastically scattered X-rays are monitored, giving the dynamic structure factor S. From this many properties of materials can be obtained, the specific property depending on the scale of the energy transfer, the table below, listing techniques, is adapted from. Inelastically scattered X-rays have intermediate phases and so in principle are not useful for X-ray crystallography
8.
Octahedron
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In geometry, an octahedron is a polyhedron with eight faces, twelve edges, and six vertices. A regular octahedron is a Platonic solid composed of eight equilateral triangles, a regular octahedron is the dual polyhedron of a cube. It is a square bipyramid in any of three orthogonal orientations and it is also a triangular antiprism in any of four orientations. An octahedron is the case of the more general concept of a cross polytope. A regular octahedron is a 3-ball in the Manhattan metric, the second and third correspond to the B2 and A2 Coxeter planes. The octahedron can also be represented as a tiling. This projection is conformal, preserving angles but not areas or lengths, straight lines on the sphere are projected as circular arcs on the plane. An octahedron with edge length √2 can be placed with its center at the origin and its vertices on the coordinate axes, the Cartesian coordinates of the vertices are then. In an x–y–z Cartesian coordinate system, the octahedron with center coordinates, additionally the inertia tensor of the stretched octahedron is I =. These reduce to the equations for the regular octahedron when x m = y m = z m = a 22, the interior of the compound of two dual tetrahedra is an octahedron, and this compound, called the stella octangula, is its first and only stellation. Correspondingly, an octahedron is the result of cutting off from a regular tetrahedron. One can also divide the edges of an octahedron in the ratio of the mean to define the vertices of an icosahedron. There are five octahedra that define any given icosahedron in this fashion, octahedra and tetrahedra can be alternated to form a vertex, edge, and face-uniform tessellation of space, called the octet truss by Buckminster Fuller. This is the only such tiling save the regular tessellation of cubes, another is a tessellation of octahedra and cuboctahedra. The octahedron is unique among the Platonic solids in having a number of faces meeting at each vertex. Consequently, it is the member of that group to possess mirror planes that do not pass through any of the faces. Using the standard nomenclature for Johnson solids, an octahedron would be called a square bipyramid, truncation of two opposite vertices results in a square bifrustum. The octahedron is 4-connected, meaning that it takes the removal of four vertices to disconnect the remaining vertices and it is one of only four 4-connected simplicial well-covered polyhedra, meaning that all of the maximal independent sets of its vertices have the same size
9.
Dodecahedron
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In geometry, a dodecahedron is any polyhedron with twelve flat faces. The most familiar dodecahedron is the dodecahedron, which is a Platonic solid. There are also three regular star dodecahedra, which are constructed as stellations of the convex form, all of these have icosahedral symmetry, order 120. The pyritohedron is a pentagonal dodecahedron, having the same topology as the regular one. The rhombic dodecahedron, seen as a case of the pyritohedron has octahedral symmetry. The elongated dodecahedron and trapezo-rhombic dodecahedron variations, along with the rhombic dodecahedra are space-filling, there are a large number of other dodecahedra. The convex regular dodecahedron is one of the five regular Platonic solids, the dual polyhedron is the regular icosahedron, having five equilateral triangles around each vertex. Like the regular dodecahedron, it has twelve pentagonal faces. However, the pentagons are not constrained to be regular, and its 30 edges are divided into two sets – containing 24 and 6 edges of the same length. The only axes of symmetry are three mutually perpendicular twofold axes and four threefold axes. Note that the regular dodecahedron can occur as a shape for quasicrystals with icosahedral symmetry. Its name comes from one of the two common crystal habits shown by pyrite, the one being the cube. The coordinates of the eight vertices of the cube are, The coordinates of the 12 vertices of the cross-edges are. When h =1, the six cross-edges degenerate to points, when h =0, the cross-edges are absorbed in the facets of the cube, and the pyritohedron reduces to a cube. When h = √5 − 1/2, the inverse of the golden ratio, a reflected pyritohedron is made by swapping the nonzero coordinates above. The two pyritohedra can be superimposed to give the compound of two dodecahedra as seen in the image here, the regular dodecahedron represents a special intermediate case where all edges and angles are equal. A tetartoid is a dodecahedron with chiral tetrahedral symmetry, like the regular dodecahedron, it has twelve identical pentagonal faces, with three meeting in each of the 20 vertices. However, the pentagons are not regular and the figure has no fivefold symmetry axes, although regular dodecahedra do not exist in crystals, the tetartoid form does
10.
Calcite
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Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate. The Mohs scale of hardness, based on scratch hardness comparison. Other polymorphs of calcium carbonate are the minerals aragonite and vaterite, aragonite will change to calcite at 380–470 °C, and vaterite is even less stable. Calcite is derived from the German Calcit, a term coined in the 19th century from the Latin word for lime and it is thus etymologically related to chalk. Calcite crystals are trigonal-rhombohedral, though actual calcite rhombohedra are rare as natural crystals, however, they show a remarkable variety of habits including acute to obtuse rhombohedra, tabular forms, prisms, or various scalenohedra. Calcite exhibits several twinning types adding to the variety of observed forms and it may occur as fibrous, granular, lamellar, or compact. Cleavage is usually in three directions parallel to the rhombohedron form and its fracture is conchoidal, but difficult to obtain. It has a defining Mohs hardness of 3, a gravity of 2.71. Color is white or none, though shades of gray, red, orange, yellow, green, blue, violet, brown, calcite is transparent to opaque and may occasionally show phosphorescence or fluorescence. A transparent variety called Iceland spar is used for optical purposes, acute scalenohedral crystals are sometimes referred to as dogtooth spar while the rhombohedral form is sometimes referred to as nailhead spar. Single calcite crystals display an optical property called birefringence and this strong birefringence causes objects viewed through a clear piece of calcite to appear doubled. The birefringent effect was first described by the Danish scientist Rasmus Bartholin in 1669, at a wavelength of ~590 nm calcite has ordinary and extraordinary refractive indices of 1.658 and 1.486, respectively. Between 190 and 1700 nm, the refractive index varies roughly between 1.9 and 1.5, while the extraordinary refractive index varies between 1.6 and 1.4. Calcite, like most carbonates, will dissolve with most forms of acid, calcite can be either dissolved by groundwater or precipitated by groundwater, depending on several factors including the water temperature, pH, and dissolved ion concentrations. Although calcite is fairly insoluble in water, acidity can cause dissolution of calcite. Ambient carbon dioxide, due to its acidity, has a slight solubilizing effect on calcite, calcite exhibits an unusual characteristic called retrograde solubility in which it becomes less soluble in water as the temperature increases. When conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together or it can fill fractures. On a landscape scale, continued dissolution of calcium carbonate-rich rocks can lead to the expansion and eventual collapse of cave systems, high-grade optical calcite was used in World War II for gun sights, specifically in bomb sights and anti-aircraft weaponry
11.
Rutile
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Rutile is a mineral composed primarily of titanium dioxide, TiO2. Rutile is the most common form of TiO2. Three rarer polymorphs of TiO2 are known, Anatase, a metastable tetragonal mineral of pseudo-octahedral habit Brookite, an orthorhombic mineral TiO2, rutile has among the highest refractive indices at visible wavelengths of any known crystal, and also exhibits a particularly large birefringence and high dispersion. Owing to these properties, it is useful for the manufacture of optical elements, especially polarization optics, for longer visible. Natural rutile may contain up to 10% iron and significant amounts of niobium and tantalum, rutile derives its name from the Latin rutilus, red, in reference to the deep red color observed in some specimens when viewed by transmitted light. Rutile is an accessory mineral in high-temperature and high-pressure metamorphic rocks. Thermodynamically, rutile is the most stable polymorph of TiO2 at all temperatures, consequently, the transformation of the metastable TiO2 polymorphs to rutile is irreversible. As it has the lowest molecular volume of the three polymorphs, it is generally the primary titanium bearing phase in most high-pressure metamorphic rocks. The occurrence of large specimen crystals is most common in pegmatites, skarns, rutile is found as an accessory mineral in some altered igneous rocks, and in certain gneisses and schists. In groups of acicular crystals it is frequently seen penetrating quartz as in the fléches damour from Graubünden, in 2005 the Republic of Sierra Leone in West Africa had a production capacity of 23% of the worlds annual rutile supply, which rose to approximately 30% in 2008. The reserves, lasting for about 19 years, are estimated at 259,000,000 metric tons, rutile has a body-centred tetragonal unit cell, with unit cell parameters a=b=4.584 Å, and c=2.953 Å. The titanium cations have a number of 6 meaning they are surrounded by an octahedron of 6 oxygen atoms. The oxygen anions have a number of 3 resulting in a trigonal planar co-ordination. Rutile also shows a screw axis when its octahedra are viewed sequentially, rutile crystals are most commonly observed to exhibit a prsimatic or acicular growth habit with preferential orientation along their c-axis, the direction. This growth habit is favored as the facets of rutile exhibit the lowest surface free energy and are therefore thermodynamically most stable, the c-axis oriented growth of rutile appears clearly in nanorods, nanowires and Abnormal grain growth phenomena of this phase. In large enough quantities in beach sands, rutile forms an important constituent of heavy minerals, miners extract and separate the valuable minerals—e. g. The main uses for rutile are the manufacture of ceramic, as a pigment. Finely powdered rutile is a brilliant white pigment and is used in paints, plastics, paper, foods, titanium dioxide pigment is the single greatest use of titanium worldwide
12.
Cassiterite
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Cassiterite is a tin oxide mineral, SnO2. It is generally opaque, but it is translucent in thin crystals and its luster and multiple crystal faces produce a desirable gem. Cassiterite has been the chief tin ore throughout ancient history and remains the most important source of tin today, most sources of cassiterite today are found in alluvial or placer deposits containing the resistant weathered grains. The best sources of primary cassiterite are found in the tin mines of Bolivia, rwanda has a nascent cassiterite mining industry. Fighting over cassiterite deposits is a cause of the conflict waged in eastern parts of the Democratic Republic of the Congo. This has led to cassiterite being considered a conflict mineral, cassiterite is a widespread minor constituent of igneous rocks. The Bolivian veins and the old exhausted workings of Cornwall, England, are concentrated in high temperature quartz veins, the veins commonly contain tourmaline, topaz, fluorite, apatite, wolframite, molybdenite, and arsenopyrite. The mineral occurs extensively in Cornwall as surface deposits on Bodmin Moor, for example, the current major tin production comes from placer or alluvial deposits in Malaysia, Thailand, Indonesia, the Maakhir region of Somalia, and Russia. Hydraulic mining methods are used to concentrate mined ore, a process which relies on the specific gravity of the SnO2 ore. Crystal twinning is common in cassiterite and most aggregate specimens show crystal twins, the typical twin is bent at a near-60-degree angle, forming an elbow twin. Botryoidal or reniform cassiterite is called wood tin, cassiterite is also used as a gemstone and collector specimens when quality crystals are found
13.
Aragonite
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Aragonite is a carbonate mineral, one of the two most common, naturally occurring, crystal forms of calcium carbonate, CaCO3. It is formed by biological and physical processes, including precipitation from marine, aragonites crystal lattice differs from that of calcite, resulting in a different crystal shape, an orthorhombic crystal system with acicular crystal. Repeated twinning results in pseudo-hexagonal forms, Aragonite may be columnar or fibrous, occasionally in branching stalactitic forms called flos-ferri from their association with the ores at the Carinthian iron mines. The type location for aragonite is Molina de Aragón,25 km from Aragon for which it was named in 1797, an aragonite cave, the Ochtinská Aragonite Cave, is situated in Slovakia. In the US, aragonite in the form of stalactites and cave flowers is known from Carlsbad Caverns, massive deposits of oolitic aragonite sand are found on the seabed in the Bahamas. Aragonite is the high pressure polymorph of calcium carbonate, as such, it occurs in high pressure metamorphic rocks such as those formed at subduction zones. Aragonite forms naturally in almost all mollusk shells, and as the calcareous endoskeleton of warm-, because the mineral deposition in mollusk shells is strongly biologically controlled, some crystal forms are distinctively different from those of inorganic aragonite. In some mollusks, the shell is aragonite, in others. The nacreous layer of the fossil shells of some extinct ammonites forms an iridescent material called ammolite. Aragonite also forms in the ocean and in caves as inorganic precipitates called marine cements and speleothems, Aragonite is not uncommon in serpentinites where high Mg in pore solutions apparently inhibits calcite growth and promotes aragonite precipitation. Aragonite is metastable at the low pressures near the Earths surface and is commonly replaced by calcite in fossils. Aragonite older than the Carboniferous is essentially unknown and it can also be synthesized by adding a calcium chloride solution to a sodium carbonate solution at temperatures above 60 °C or in water-ethanol mixtures at ambient temperatures. Aragonite is thermodynamically unstable at temperature and pressure, and tends to alter to calcite on scales of 107 to 108 years. The mineral vaterite, also known as μ-CaCO3, is another phase of calcium carbonate that is metastable at ambient conditions typical of Earths surface, in aquaria, aragonite is considered essential for the replication of reef conditions. Aragonite provides the necessary for much sea life and also keeps the pH of the water close to its natural level. Aragonite has been tested for the removal of pollutants like zinc, cobalt. Aragonite sea Ikaite, CaCO3·6H2O Monohydrocalcite, CaCO3·H2O Nacre, otherwise known as Mother-of-Pearl Oolitic aragonite sand The Ochtinska aragonite cave Kosovo Caves Aragonite Formations
14.
Chrysoberyl
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The mineral or gemstone chrysoberyl is an aluminate of beryllium with the formula BeAl2O4. The name chrysoberyl is derived from the Greek words χρυσός chrysos and βήρυλλος beryllos, despite the similarity of their names, chrysoberyl and beryl are two completely different gemstones, although they both contain beryllium. Chrysoberyl is the third-hardest frequently encountered natural gemstone and lies at 8.5 on the hardness scale, an interesting feature of its crystals are the cyclic twins called trillings. These twinned crystals have an appearance, but are the result of a triplet of twins with each twin oriented at 120° to its neighbors. If only two of the three possible twin orientations are present, a V-shaped twin results, ordinary chrysoberyl is yellowish-green and transparent to translucent. When the mineral exhibits good pale green to yellow color and is transparent, the three main varieties of chrysoberyl are, ordinary yellow-to-green chrysoberyl, cats eye or cymophane, and alexandrite. Alexandrite, a strongly pleochroic gem, will exhibit emerald green, red, however, its most distinctive property is that it also changes color in artificial light compared to daylight. Which of these prevails to give the perceived hue depends on the balance of the illumination. Fine-quality alexandrite has a green to bluish-green color in daylight, changing to a red to purplish-red color in incandescent light, however, fine-color material is extremely rare. Less-desirable stones may have daylight colors of yellowish-green and incandescent colors of brownish red, cymophane is popularly known as cats eye. This variety exhibits pleasing chatoyancy or opalescence that reminds one of the eye of a cat, when cut to produce a cabochon, the mineral forms a light-green specimen with a silky band of light extending across the surface of the stone. Chrysoberyl forms as a result of pegmatitic processes, melting in the Earths crust produces relatively low-density molten magma which can rise upwards towards the surface. The remnant magma thus becomes richer in water, and also in rare elements that similarly do not fit in the structures of major rock-forming minerals. The high water content of the magma made it possible for the crystals to grow quickly, so pegmatite crystals are quite large. Chrysoberyl can also grow in the rocks near to pegmatites. Hence, it can be found in mica schists and in contact metamorphic deposits of dolomitic marble. When found in placers, it will have rounded edges instead of sharp. Much of the chrysoberyl mined in Brazil and Sri Lanka is recovered from placers, if the pegmatite fluid is rich in beryllium, crystals of beryl or chrysoberyl could form
15.
Cerussite
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Cerussite is a mineral consisting of lead carbonate, and an important ore of lead. The name is from the Latin cerussa, white lead, cerussa nativa was mentioned by Conrad Gessner in 1565, and in 1832 F. S. Beudant applied the name cruise to the mineral, whilst the present form, cerussite, is due to W. Haidinger. Miners names in use were lead-spar and white-lead-ore. Cerussite crystallizes in the system and is isomorphous with aragonite. Like aragonite it is very frequently twinned, the compound crystals being pseudo-hexagonal in form, three crystals are usually twinned together on two faces of the prism, producing six-rayed stellate groups with the individual crystals intercrossing at angles of nearly 60°. Crystals are of frequent occurrence and they usually have very bright, the mineral also occurs in compact granular masses, and sometimes in fibrous forms. The mineral is colorless or white, sometimes grey or greenish in tint. It is very brittle, and has a conchoidal fracture and it has a Mohs hardness of 3 to 3.75 and a specific gravity of 6.5. A variety containing 7% of zinc carbonate, replacing lead carbonate, is known as iglesiasite, from Iglesias in Sardinia, the mineral may be readily recognized by its characteristic twinning, in conjunction with the adamantine lustre and high specific gravity. It dissolves with effervescence in nitric acid. A blowpipe test will cause it to fuse very readily, delicate acicular crystals of considerable length were found long ago in the Pentire Glaze mine near St Minver in Cornwall. Cerussite is often found in quantities, and has a lead content of up to 77. 5%. Lead carbonate is insoluble in neutral water, but will dissolve in dilute acids. White lead is the key ingredient in lead paints, ingestion of lead-based paint chips is the most common cause of lead poisoning in children. Both white lead and lead acetate have been used in cosmetics throughout history, though this practice has ceased in Western countries
16.
Orthoclase
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Orthoclase, or orthoclase feldspar, is an important tectosilicate mineral which forms igneous rock. The name is from the Ancient Greek for straight fracture, because its two planes are at right angles to each other. It is a type of potassium feldspar, also known as K-feldspar, the gem known as moonstone is largely composed of orthoclase. Orthoclase is a constituent of most granites and other felsic igneous rocks and often forms huge crystals. Typically, the pure potassium endmember of orthoclase forms a solution with albite. While slowly cooling within the earth, sodium-rich albite lamellae form by exsolution, the resulting intergrowth of the two feldspars is called perthite. The higher-temperature polymorph of KAlSi3O8 is sanidine, sanidine is common in rapidly cooled volcanic rocks such as obsidian and felsic pyroclastic rocks, and is notably found in trachytes of the Drachenfels, Germany. The lower-temperature polymorph of KAlSi3O8 is microcline, adularia is a low temperature form of either microcline or orthoclase originally reported from the low temperature hydrothermal deposits in the Adula Alps of Switzerland. It was first described by Ermenegildo Pini in 1781, the optical effect of adularescence in moonstone is typically due to adularia. The largest documented crystal of orthoclase was found in Ural mountains. It measured ~10×10×0.4 m and weighed ~100 tons, together with the other potassium feldspars, orthoclase is a common raw material for the manufacture of some glasses and some ceramics such as porcelain, and as a constituent of scouring powder. Some intergrowths of orthoclase and albite have an attractive pale luster and are called moonstone when used in jewellery, most moonstones are translucent and white, although grey and peach-colored varieties also occur. In gemology, their luster is called adularescence and is described as creamy or silvery white with a billowy quality. It is the gem of Florida. Orthoclase is one of the ten defining minerals of the Mohs scale of mineral hardness, nASAs Curiosity Rover discovery of high levels of orthoclase in Martian sandstones suggested that some Martian rocks may have experienced complex geological processing, such as repeated melting
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Gypsum
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Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is widely mined and is used as a fertilizer, and as the constituent in many forms of plaster, blackboard chalk. Mohs scale of hardness, based on scratch Hardness comparison. It forms as a mineral and as a hydration product of anhydrite. The word gypsum is derived from the Greek word γύψος, plaster, because the quarries of the Montmartre district of Paris have long furnished burnt gypsum used for various purposes, this dehydrated gypsum became known as plaster of Paris. Upon addition of water, after a few tens of minutes plaster of Paris becomes regular gypsum again, causing the material to harden or set in ways that are useful for casting, Gypsum was known in Old English as spærstān, spear stone, referring to its crystalline projections. Gypsum may act as a source of sulfur for plant growth, which was discovered by J. M. Mayer, american farmers were so anxious to acquire it that a lively smuggling trade with Nova Scotia evolved, resulting in the so-called Plaster War of 1820. In the 19th century, it was known as lime sulfate or sulfate of lime. Gypsum is moderately water-soluble and, in contrast to most other salts, it exhibits retrograde solubility, when gypsum is heated in air it loses water and converts first to calcium sulfate hemihydrate, and, if heated further, to anhydrous calcium sulfate. As for anhydrite, its solubility in saline solutions and in brines is also dependent on NaCl concentration. Gypsum crystals are found to contain water and hydrogen bonding. Gypsum occurs in nature as flattened and often twinned crystals, and transparent, selenite contains no significant selenium, rather, both substances were named for the ancient Greek word for the Moon. Selenite may also occur in a silky, fibrous form, in case it is commonly called satin spar. Finally, it may also be granular or quite compact, in hand-sized samples, it can be anywhere from transparent to opaque. A very fine-grained white or lightly tinted variety of gypsum, called alabaster, is prized for ornamental work of various sorts, in arid areas, gypsum can occur in a flower-like form, typically opaque, with embedded sand grains called desert rose. It also forms some of the largest crystals found in nature, up to 12 m long, Gypsum is a common mineral, with thick and extensive evaporite beds in association with sedimentary rocks. Deposits are known to occur in strata from as far back as the Archaean eon, Gypsum is deposited from lake and sea water, as well as in hot springs, from volcanic vapors, and sulfate solutions in veins. Hydrothermal anhydrite in veins is commonly hydrated to gypsum by groundwater in near-surface exposures and it is often associated with the minerals halite and sulfur
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Feldspar
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Feldspars are a group of rock-forming tectosilicate minerals that make up about 40% of the Earths continental crust. Feldspars crystallize from magma as veins in both intrusive and extrusive rocks and are also present in many types of metamorphic rock. Rock formed almost entirely of plagioclase feldspar is known as anorthosite. Feldspars are also found in types of sedimentary rocks. The name feldspar derives from the German Feldspat, a compound of the words Feld, field, and Spat, the change from Spat to -spar was influenced by the English word spar, a synonym for mineral. Feldspathic refers to materials that contain feldspar, the alternate spelling, felspar, has largely fallen out of use. This group of minerals consists of tectosilicates, solid solutions between albite and anorthite are called plagioclase, or more properly plagioclase feldspar. Only limited solid solution occurs between K-feldspar and anorthite, and in the two solid solutions, immiscibility occurs at temperatures common in the crust of the earth. Albite is considered both a plagioclase and alkali feldspar, the alkali feldspars are as follows, orthoclase —KAlSi3O8 sanidine —AlSi3O8 microcline —KAlSi3O8 anorthoclase —AlSi3O8 Sanidine is stable at the highest temperatures, and microcline at the lowest. Perthite is a texture in alkali feldspar, due to exsolution of contrasting alkali feldspar compositions during cooling of an intermediate composition. The perthitic textures in the alkali feldspars of many granites can be seen with the naked eye, microperthitic textures in crystals are visible using a light microscope, whereas cryptoperthitic textures can be seen only with an electron microscope. Barium feldspars are also considered alkali feldspars, barium feldspars form as the result of the substitution of barium for potassium in the mineral structure. The barium feldspars are monoclinic and include the following, celsian—BaAl2Si2O8 hyalophane—4O8 The plagioclase feldspars are triclinic, the immiscibility gaps in the plagioclase solid solutions are complex compared to the gap in the alkali feldspars. The play of colours visible in some feldspar of labradorite composition is due to very fine-grained exsolution lamellae, chemical weathering of feldspars results in the formation of clay minerals. About 20 million tonnes of feldspar were produced in 2010, mostly by three countries, Italy, Turkey, and China, Feldspar is a common raw material used in glassmaking, ceramics, and to some extent as a filler and extender in paint, plastics, and rubber. In glassmaking, alumina from feldspar improves product hardness, durability, in ceramics, the alkalis in feldspar act as a flux, lowering the melting temperature of a mixture. Fluxes melt at a stage in the firing process, forming a glassy matrix that bonds the other components of the system together. In the US, about 66% of feldspar is consumed in glassmaking, including glass containers, ceramics and other uses, such as fillers, accounted for the remainder
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Plagioclase
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Plagioclase is a series of tectosilicate minerals within the feldspar group. Rather than referring to a mineral with a specific chemical composition, plagioclase is a continuous solid solution series. This was first shown by the German mineralogist Johann Friedrich Christian Hessel in 1826, the series ranges from albite to anorthite endmembers, where sodium and calcium atoms can substitute for each other in the minerals crystal lattice structure. Plagioclase in hand samples is often identified by its polysynthetic crystal twinning or record-groove effect, plagioclase is a major constituent mineral in the Earths crust, and is consequently an important diagnostic tool in petrology for identifying the composition, origin and evolution of igneous rocks. Plagioclase is also a constituent of rock in the highlands of the Earths moon. Analysis of thermal emission spectra from the surface of Mars suggests that plagioclase is the most abundant mineral in the crust of Mars, the extinction angle is an optical characteristic and varies with the albite fraction. There are several named plagioclase feldspars that fall between albite and anorthite in the series, the following table shows their compositions in terms of constituent anorthite and albite percentages. Anorthite was named by Gustav Rose in 1823 from the Ancient Greek meaning oblique, anorthite is a comparatively rare mineral but occurs in the basic plutonic rocks of some orogenic calc-alkaline suites. Albite is named from the Latin albus, in reference to its pure white color. It is a common and important rock-making mineral associated with the more acid rock types and in pegmatite dikes, often with rarer minerals like tourmaline. The intermediate members of the group are very similar to each other. Bytownite, named after the name for Ottawa, Canada, is a rare mineral occasionally found in more basic rocks. Labradorite is the characteristic feldspar of the basic rock types such as diorite, gabbro, andesite. Labradorite frequently shows an iridescent display of colors due to light refracting within the lamellae of the crystal and it is named after Labrador, where it is a constituent of the intrusive igneous rock anorthosite which is composed almost entirely of plagioclase. A variety of known as spectrolite is found in Finland. Andesine is a mineral of rocks such as diorite which contain a moderate amount of silica. Oligoclase is common in granite, syenite, diorite, and gneiss and it is a frequent associate of orthoclase. The name oligoclase is derived from the Greek for little and fracture, sunstone is mainly oligoclase with flakes of hematite
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Microcline
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Microcline is an important igneous rock-forming tectosilicate mineral. It is an alkali feldspar. Microcline typically contains minor amounts of sodium and it is common in granite and pegmatites. Microcline forms during cooling of orthoclase, it is more stable at lower temperatures than orthoclase. Sanidine is a polymorph of alkali feldspar stable at yet higher temperature and it is a fully ordered triclinic modification of potassium feldspar and is dimorphous with orthoclase. Perthite is either microcline or orthoclase with thin lamellae of exsolved albite, Amazon stone, or amazonite, is a green variety of microcline. It is not found anywhere in the Amazon Basin, however, the Spanish explorers who named it apparently confused it with another green mineral from that region. The largest documented single crystals of microcline were found in Devils Hole Beryl Mine, Colorado, US and this could be one of the largest crystals of any material found so far. Microcline is commonly used for the manufacturing of porcelain, list of minerals Alkali feldspars U
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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
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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
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Metazeunerite
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Metazeunerite is an arsenate mineral with a chemical formula of Cu22·8H2O. The origin of this comes from the dehydration process that metazeunerite must go through. As dehydration occurs, zeunerite loses an electron and is then metamorphosed into metazeunerite, when looking at a thin section, metzeunerite is anisotropic, meaning that it has pleochroism. When a mineral is anisotropic, one can see whether it is uniaxial or biaxial and this mineral is uniaxial negative due to the ordinary ray being slower than the extraordinary ray. Metazeunerite is an uncommon secondary mineral found in arsenic bearing hydrothermal uranium deposits across the world. This widespread mineral occurs specifically in Europe, western North America, Australia, Brazil and Chile, Namibia and it is currently studied through thermal decomposition by calculating the different levels of dehydration, as zeunerite is transformed into metazeunerite
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Staurolite
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Staurolite is a red brown to black, mostly opaque, nesosilicate mineral with a white streak. It crystallizes in the crystal system, has a Mohs hardness of 7 to 7.5. Magnesium, zinc and manganese substitute in the site and trivalent iron can substitute for aluminium. Staurolite often occurs twinned in a characteristic cross-shape, called cruciform penetration twinning, in handsamples, macroscopically visible staurolite crystals are of prismatic shape. In thin sections staurolite is commonly twinned and shows lower first order birefringence similar to quartz and it can be identified in metamorphic rocks by its swiss cheese appearance and often mantled porphyroblastic character. The name is derived from the Greek, stauros for cross, staurolite is a regional metamorphic mineral of intermediate to high grade. It occurs with almandine garnet, micas, kyanite, as well as albite, biotite and it is the official state mineral of the U. S. state of Georgia and is also to be found in the Lepontine Alps in Switzerland. Staurolite is most commonly found in Fannin County, Georgia and it is also found in Fairy Stone State Park in Patrick County, Virginia. The park is named for a name for staurolite from a legend in the area. Samples are also found in Island Park, Idaho, near Henrys Lake, Taos, New Mexico, near Blanchard Dam in Minnesota, staurolite is one of the index minerals that are used to estimate the temperature, depth, and pressure at which a rock undergoes metamorphism
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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−
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Fluorite
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Fluorite is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals and it crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon. Mohs scale of hardness, based on scratch Hardness comparison. Fluorite is a mineral, both in visible and ultraviolet light, and the stone has ornamental and lapidary uses. Industrially, fluorite is used as a flux for smelting, and in the production of certain glasses, the purest grades of fluorite are a source of fluoride for hydrofluoric acid manufacture, which is the intermediate source of most fluorine-containing fine chemicals. Optically clear transparent fluorite lenses have low dispersion, so made from it exhibit less chromatic aberration. Fluorite optics are also usable in the range, where conventional glasses are too absorbent for use. The word fluorite is derived from the Latin verb fluere, meaning to flow, the mineral is used as a flux in iron smelting to decrease the viscosity of slags. The term flux comes from the Latin adjective fluxus, meaning flowing, loose, agricola, a German scientist with expertise in philology, mining, and metallurgy, named fluorspar as a neo-Latinization of the German Flussspat from Fluß and Spat. In 1852, fluorite gave its name to the phenomenon of fluorescence, Fluorite also gave the name to its constitutive element fluorine. Presently, the fluorspar is most commonly used for fluorite as the industrial and chemical commodity, while fluorite is used mineralogically. Fluorite crystallises in a cubic motif, crystal twinning is common and adds complexity to the observed crystal habits. Fluorite has four perfect cleavage planes that help produce octahedral fragments, element substitution for the calcium cation often includes certain rare earth elements, such as yttrium and cerium. Iron, sodium, and barium are also common impurities, some fluorine may be replaced by the chloride anion. Fluorite is a widely occurring mineral that occurs globally with significant deposits in over 9,000 areas. It may occur as a deposit, especially with metallic minerals, where it often forms a part of the gangue and may be associated with galena, sphalerite, barite, quartz. It is a mineral in deposits of hydrothermal origin and has been noted as a primary mineral in granites and other igneous rocks. The world reserves of fluorite are estimated at 230 million tonnes with the largest deposits being in South Africa, Mexico, China is leading the world production with about 3 Mt annually, followed by Mexico, Mongolia, Russia, South Africa, Spain and Namibia
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Galvanization
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Galvanization is the process of applying a protective zinc coating to steel or iron, to prevent rusting. The most common method is hot-dip galvanizing, in parts are submerged in a bath of molten zinc. Galvanizing protects the metal in three ways, It forms a coating of zinc which, when intact, prevents corrosive substances from reaching the underlying steel or iron. The zinc serves as a sacrificial anode so that if the coating is scratched. The zinc protects its base metal by corroding before iron, for better results, application of chromates over zinc is also seen as an industrial trend. The earliest known example of galvanized iron was encountered by Europeans on 17th-century Indian armor in the Royal Armouries Museum collection and it was named in English via French from the name of Italian scientist Luigi Galvani. Originally in the 19th century, the term galvanizing was used to describe the administration of electric shocks and this usage is the origin of the metaphorical use of the verb galvanize, such as to galvanize into action meaning stimulating a complacent person or group to take action. In modern usage, the term galvanizing has largely come to be associated with zinc coatings, galvanic paint, a precursor to hot-dip galvanizing, was patented by Stanislas Sorel, of Paris, in December 1837. Hot-dip galvanizing deposits a thick robust layer of iron alloys on the surface of a steel item. In the case of bodies, where additional decorative coatings of paint will be applied. The hot-dip process generally does not reduce strength on a measurable scale and this deficiency is a consideration affecting the manufacture of wire rope and other highly-stressed products. The protection provided by hot-dip galvanizing is insufficient for products that will be exposed to corrosive materials such as acids. For these applications, more expensive stainless steel is preferred, some nails made today are galvanized. Nonetheless, electroplating is used on its own for many applications because it is cheaper than hot-dip zinc coating. Another reason not to use hot-dip zinc coating is that for bolts and nuts of size M10 or smaller, the thick hot-dipped coating fills in too much of the threads, the size of crystallites in galvanized coatings is a visible and aesthetic feature, known as spangle. Visible crystallites are rare in other engineering materials, even though they are usually present, thermal diffusion galvanizing, or Sherardizing, provides a zinc diffusion coating on iron- or copper-based materials. Parts and zinc powder are tumbled in a rotating drum. Around 300 °C, zinc will diffuse into the substrate to form a zinc alloy, the advance surface preparation of the goods can be carried out by shot blasting
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Crystallite
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A crystallite is a small or even microscopic crystal which forms, for example, during the cooling of many materials. The orientation of crystallites can be random with no preferred direction, called random texture, or directed, possibly due to growth, fiber texture is an example of the latter. Crystallites are also referred to as grains, the areas where crystallite grains meet are known as grain boundaries. Polycrystalline or multicrystalline materials, or polycrystals are solids that are composed of many crystallites of varying size, most inorganic solids are polycrystalline, including all common metals, many ceramics, rocks and ice. The extent to which a solid is crystalline has important effects on its physical properties, sulfur, while usually polycrystalline, may also occur in other allotropic forms with completely different properties. Although crystallites are referred to as grains, powder grains are different, while the structure of a crystal is highly ordered and its lattice is continuous and unbroken. Amorphous materials, such as glass and many polymers, are non-crystalline, Polycrystalline structures and paracrystalline phases are in between these two extremes. Crystal size is measured from X-ray diffraction patterns and grain size by other experimental techniques like transmission electron microscopy. Solid objects that are enough to see and handle are rarely composed of a single crystal. Most materials are polycrystalline, they are made of a number of single crystals — crystallites — held together by thin layers of amorphous solid. The crystallite size can vary from a few nanometers to several millimeters, if the individual crystallites are oriented completely at random, a large enough volume of polycrystalline material will be approximately isotropic. This property helps the simplifying assumptions of continuum mechanics to apply to real-world solids, however, most manufactured materials have some alignment to their crystallites, resulting in texture that must be taken into account for accurate predictions of their behavior and characteristics. When the crystallites are mostly ordered with just some random spread of orientations, material fractures can be intergranular fracture or a transgranular fracture. There is an ambiguity with powder grains, a grain can be made of several crystallites. Thus, the size found by laser granulometry can be different from the grain size found by X-ray diffraction, by optical microscopy under polarised light. Coarse grained rocks are formed very slowly, while fine grained rocks are formed quickly, if a rock forms very quickly, such as the solidification of lava ejected from a volcano, there may be no crystals at all. Grain boundaries are interfaces where crystals of different orientations meet, a grain boundary is a single-phase interface, with crystals on each side of the boundary being identical except in orientation. The term crystallite boundary is sometimes, though rarely, used, grain boundary areas contain those atoms that have been perturbed from their original lattice sites, dislocations, and impurities that have migrated to the lower energy grain boundary
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Metamorphism
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Metamorphism is the change of minerals or geologic texture in pre-existing rocks, without the protolith melting into liquid magma. The change occurs primarily due to heat, pressure, and the introduction of chemically active fluids, the chemical components and crystal structures of the minerals making up the rock may change even though the rock remains a solid. Changes at or just beneath Earths surface due to weathering and/or diagenesis are not classified as metamorphism, Metamorphism typically occurs between diagenesis, and melting. Three types of metamorphism exist, contact, dynamic, and regional, Metamorphism produced with increasing pressure and temperature conditions is known as prograde metamorphism. Conversely, decreasing temperatures and pressure characterize retrograde metamorphism, Metamorphic rocks can change without melting. When pressure is applied, somewhat flattened grains that orient in the same direction have a stable configuration. The upper boundary of metamorphic conditions is related to the onset of melting processes in the rock, the maximum temperature for metamorphism is typically 700 –900 °C, depending on the pressure and on the composition of the rock. Migmatites are rocks formed at this limit, which contain pods. Since the 1980s it has recognized that rocks are rarely dry enough. Conditions producing widespread regionally metamorphosed rocks occur during an orogenic event, the collision of two continental plates or island arcs with continental plates produce the extreme compressional forces required for the metamorphic changes typical of regional metamorphism. These orogenic mountains are eroded, exposing the intensely deformed rocks typical of their cores. The conditions within the slab as it plunges toward the mantle in a subduction zone also produce regional metamorphic effects. The techniques of structural geology are used to unravel the collisional history, regional metamorphism can be described and classified into metamorphic facies or metamorphic zones of temperature/pressure conditions throughout the orogenic terrane. Contact metamorphism occurs typically around intrusive igneous rocks as a result of the increase caused by the intrusion of magma into cooler country rock. The area surrounding the intrusion where the contact metamorphism effects are present is called the metamorphic aureole, contact metamorphic rocks are usually known as hornfels. Rocks formed by contact metamorphism may not present signs of deformation and are often fine-grained. Contact metamorphism is greater adjacent to the intrusion and dissipates with distance from the contact, the size of the aureole depends on the heat of the intrusion, its size, and the temperature difference with the wall rocks. Dikes generally have small aureoles with minimal metamorphism whereas large ultramafic intrusions can have significantly thick, the metamorphic grade of an aureole is measured by the peak metamorphic mineral which forms in the aureole
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Orogeny
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An Orogeny is an event that leads to a large structural deformation of the Earths lithosphere due to the interaction between tectonic plates. Orogens or orogenic belts develop when a plate is crumpled and is pushed upwards to form mountain ranges. Orogeny is the mechanism by which mountains are built on continents. The word orogeny comes from Ancient Greek, though it was used before him, the term was employed by the American geologist G. K. Gilbert in 1890 to describe the process of mountain building as distinguished from epeirogeny. Formation of an orogen is accomplished in part by the processes of subduction or convergence of two or more continents. Orogeny usually produces long arcuate structures, known as orogenic belts, generally, orogenic belts consist of long parallel strips of rock exhibiting similar characteristics along the length of the belt. Orogenic belts are associated with zones, which consume crust, produce volcanoes. Geologists attribute the arcuate structure to the rigidity of the descending plate and these island arcs may be added to a continent during an orogenic event. The processes of orogeny can take tens of millions of years, frequently, rock formations that undergo orogeny are severely deformed and undergo metamorphism. Orogenic processes may push deeply buried rocks to the surface, sea-bottom and near-shore material may cover some or all of the orogenic area. If the orogeny is due to two continents colliding, very high mountains can result, an orogenic event may be studied, as a tectonic structural event, as a geographical event, and as a chronological event. The foreland basin forms ahead of the orogen due mainly to loading and resulting flexure of the lithosphere by the mountain belt. The basin migrates with the front and early deposited foreland basin sediments become progressively involved in folding and thrusting. Sediments deposited in the basin are mainly derived from the erosion of the actively uplifting rocks of the mountain range. The fill of many such shows an change in time from deepwater marine through shallow water to continental sediments. Although orogeny involves plate tectonics, the tectonic forces result in a variety of associated phenomena, including magmatism, metamorphism, crustal melting, what exactly happens in a specific orogen depends upon the strength and rheology of the continental lithosphere, and how these properties change during orogenesis. In addition to orogeny, the orogen is subject to other processes, for example, the Caledonian Orogeny refers to the Silurian and Devonian events that resulted from the collision of Laurentia with Eastern Avalonia and other former fragments of Gondwana. The Caledonian Orogen resulted from events and various others that are part of its peculiar orogenic cycle
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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
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Cubic crystal system
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In crystallography, the cubic crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals, there are three main varieties of these crystals, Primitive cubic Body-centered cubic, Face-centered cubic Each is subdivided into other variants listed below. Note that although the cell in these crystals is conventionally taken to be a cube. This is related to the fact that in most cubic crystal systems, a classic isometric crystal has square or pentagonal faces. The three Bravais lattices in the crystal system are, The primitive cubic system consists of one lattice point on each corner of the cube. Each atom at a point is then shared equally between eight adjacent cubes, and the unit cell therefore contains in total one atom. The body-centered cubic system has one point in the center of the unit cell in addition to the eight corner points. It has a net total of 2 lattice points per unit cell, Each sphere in a cF lattice has coordination number 12. The face-centered cubic system is related to the hexagonal close packed system. The plane of a cubic system is a hexagonal grid. Attempting to create a C-centered cubic crystal system would result in a simple tetragonal Bravais lattice, there are a total 36 cubic space groups. Other terms for hexoctahedral are, normal class, holohedral, ditesseral central class, a simple cubic unit cell has a single cubic void in the center. Additionally, there are 24 tetrahedral voids located in a square spacing around each octahedral void and these tetrahedral voids are not local maxima and are not technically voids, but they do occasionally appear in multi-atom unit cells. A face-centered cubic unit cell has eight tetrahedral voids located midway between each corner and the center of the cell, for a total of eight net tetrahedral voids. One important characteristic of a structure is its atomic packing factor. This is calculated by assuming all the atoms are identical spheres. The atomic packing factor is the proportion of space filled by these spheres, assuming one atom per lattice point, in a primitive cubic lattice with cube side length a, the sphere radius would be a⁄2 and the atomic packing factor turns out to be about 0.524. Similarly, in a bcc lattice, the atomic packing factor is 0.680, as a rule, since atoms in a solid attract each other, the more tightly packed arrangements of atoms tend to be more common
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Homogeneity and heterogeneity
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Homogeneity and heterogeneity are concepts often used in the sciences and statistics relating to the uniformity in a substance or organism. A material or image that is homogeneous is uniform in composition or character, the alternate spellings homogenous and heterogenous are commonly, but incorrectly, used. Heterogenous meanwhile is a term primarily confined to pathology which refers to the property of an object in the body having its origin outside the body, the concepts are the same to every level of complexity, from atoms to populations of animals or people, and galaxies. Hence, an element may be homogeneous on a larger scale and this is known as an effective medium approach, or effective medium approximations. Various disciplines understand heterogeneity, or being heterogeneous, in different ways, heterogeneous solids, liquids, and gases may be made homogeneous by melting, stirring, or by allowing time to pass for diffusion to distribute the molecules evenly. For example, adding dye to water will create a solution at first. Entropy allows for heterogeneous substances to become homogeneous over time, a heterogeneous mixture is a mixture of two or more compounds. Examples are, mixtures of sand and water or sand and iron filings, a rock, water and oil, a salad, trail mix. A mixture can be determined to be homogeneous when everything is settled and equal, various models have been proposed to model the concentrations in different phases. The phenomena to be considered are mass rates and reaction, homogeneous reactions are chemical reactions in which the reactants and products are in the same phase, while heterogeneous reactions have reactants in two or more phases. Reactions that take place on the surface of a catalyst of a different phase are also heterogeneous, a reaction between two gases or two miscible liquids is homogeneous. A reaction between a gas and a liquid, a gas and a solid or a liquid and a solid is heterogeneous, earth is a heterogeneous substance in many aspects. E. g. rocks are inherently heterogeneous, usually occurring at the micro-scale and mini-scale, in algebra, homogeneous polynomials have the same number of factors of a given kind. This can cause problems in attempts to summarize the meaning of the studies, in medicine and genetics, a genetic or allelic heterogeneous condition is one where the same disease or condition can be caused, or contributed to, by several factors. In the case of genetics, varying different genes or alleles, in cancer research, cancer cell heterogeneity is thought to be one of the underlying reasons that make treatment of cancer difficult. In physics, heterogeneous is understood to mean having physical properties that vary within the medium, in sociology, heterogeneous may refer to a society or group that includes individuals of differing ethnicities, cultural backgrounds, sexes, or ages. Academic Press Dictionary of Science and Technology
34.
Gold
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Gold is a chemical element with symbol Au and atomic number 79. In its purest form, it is a bright, slightly yellow, dense, soft, malleable. Chemically, gold is a metal and a group 11 element. It is one of the least reactive chemical elements and is solid under standard conditions, Gold often occurs in free elemental form, as nuggets or grains, in rocks, in veins, and in alluvial deposits. It occurs in a solid solution series with the element silver and also naturally alloyed with copper. Less commonly, it occurs in minerals as gold compounds, often with tellurium, golds atomic number of 79 makes it one of the higher numbered, naturally occurring elements. It is thought to have produced in supernova nucleosynthesis, from the collision of neutron stars. Because the Earth was molten when it was formed, almost all of the present in the early Earth probably sank into the planetary core. Gold is resistant to most acids, though it does dissolve in aqua regia, a mixture of acid and hydrochloric acid. Gold also dissolves in solutions of cyanide, which are used in mining and electroplating. Gold dissolves in mercury, forming amalgam alloys, but this is not a chemical reaction, as a precious metal, gold has been used for coinage, jewelry, and other arts throughout recorded history. A total of 186,700 tonnes of gold is in existence above ground, the world consumption of new gold produced is about 50% in jewelry, 40% in investments, and 10% in industry. Gold is also used in infrared shielding, colored-glass production, gold leafing, certain gold salts are still used as anti-inflammatories in medicine. As of 2014, the worlds largest gold producer by far was China with 450 tonnes, Gold is cognate with similar words in many Germanic languages, deriving via Proto-Germanic *gulþą from Proto-Indo-European *ǵʰelh₃-. The symbol Au is from the Latin, aurum, the Latin word for gold, the Proto-Indo-European ancestor of aurum was *h₂é-h₂us-o-, meaning glow. This word is derived from the root as *h₂éu̯sōs, the ancestor of the Latin word Aurora. This etymological relationship is presumably behind the frequent claim in scientific publications that aurum meant shining dawn, Gold is the most malleable of all metals, a single gram can be beaten into a sheet of 1 square meter, and an avoirdupois ounce into 300 square feet. Gold leaf can be thin enough to become semi-transparent
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Grain boundary
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A grain boundary is the interface between two grains, or crystallites, in a polycrystalline material. Grain boundaries are 2D defects in the structure, and tend to decrease the electrical and thermal conductivity of the material. Most grain boundaries are preferred sites for the onset of corrosion and they are also important to many of the mechanisms of creep. It is convenient to categorize grain boundaries according to the extent of misorientation between the two grains, low-angle grain boundaries or subgrain boundaries are those with a misorientation less than about 15 degrees. Generally speaking they are composed of an array of dislocations and their properties, in contrast the properties of high-angle grain boundaries, whose misorientation is greater than about 11 degrees, are normally found to be independent of the misorientation. However, there are special boundaries at particular orientations whose interfacial energies are markedly lower than those of general HAGBs, the simplest boundary is that of a tilt boundary where the rotation axis is parallel to the boundary plane. This boundary can be conceived as forming from a single, contiguous crystallite or grain which is bent by some external force. As the grain is bent further, more and more dislocations must be introduced to accommodate the resulting in a growing wall of dislocations – a low-angle boundary. The grain can now be considered to have split into two sub-grains of related crystallography but notably different orientations, an alternative is a twist boundary where the misorientation occurs around an axis that is perpendicular to the boundary plane. This type of boundary incorporates two sets of screw dislocations, if the Burgers vectors of the dislocations are orthogonal, then the dislocations do not strongly interact and form a square network. In other cases, the dislocations may interact to form a more complex hexagonal structure and these concepts of tilt and twist boundaries represent somewhat idealized cases. The majority of boundaries are of a type, containing dislocations of different types and Burgers vectors. If the dislocations in the boundary remain isolated and distinct, the boundary can be considered to be low-angle, if deformation continues, the density of dislocations will increase and so reduce the spacing between neighboring dislocations. Eventually, the cores of the dislocations will begin to overlap, at this point the boundary can be considered to be high-angle and the original grain to have separated into two entirely separate grains. In comparison to LAGBs, high-angle boundaries are considerably more disordered, with areas of poor fit. Indeed, they were thought to be some form of amorphous or even liquid layer between the grains. It is now accepted that a boundary consists of units which depend on both the misorientation of the two grains and the plane of the interface. In coincident site lattice theory, the degree of fit between the structures of the two grains is described by the reciprocal of the ratio of coincidence sites to the number of sites
36.
Work hardening
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Work hardening, also known as strain hardening or cold working, is the strengthening of a metal by plastic deformation. This strengthening occurs because of dislocation movements and dislocation generation within the structure of the material. Many non-brittle metals with a high melting point as well as several polymers can be strengthened in this fashion. Alloys not amenable to treatment, including low-carbon steel, are often work-hardened. Some materials cannot be work-hardened at low temperatures, such as indium, however others can only be strengthened via work hardening, such as pure copper, Work hardening may be desirable or undesirable depending on the context. An example of work hardening is during machining when early passes of a cutter inadvertently work-harden the workpiece surface. Certain alloys are prone to this than others, superalloys such as Inconel require machining strategies that take it into account. An example of work hardening is that which occurs in metalworking processes that intentionally induce plastic deformation to exact a shape change. These processes are known as working or cold forming processes. They are characterized by shaping the workpiece at a temperature below its recrystallization temperature, cold forming techniques are usually classified into four major groups, squeezing, bending, drawing, and shearing. Applications include the heading of bolts and cap screws and the finishing of cold rolled steel, in cold forming, metal is formed at high speed and high pressure using tool steel or carbide dies. The cold working of the increasing the hardness, yield strength. Copper was the first metal in use for tools and containers since it is one of the few metals available in non-oxidized form. Copper is easily softened by heating and then cooling, in this annealed state it may then be hammered, stretched and otherwise formed, progressing toward the desired final shape, but becoming harder and less ductile as work progresses. If work continues beyond a certain hardness the metal will tend to fracture when worked, annealing is stopped when the workpiece is near its final desired shape, and so the final product will have a desired stiffness and hardness. The technique of repoussé exploits these properties of copper, enabling the construction of durable jewelry articles and sculptures, for this reason modern aluminum aircraft will have an imposed working lifetime, after which the aircraft must be retired. Before work hardening, the lattice of the material exhibits a regular, the defect-free lattice can be created or restored at any time by annealing. As the material is work hardened it becomes saturated with new dislocations
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Dislocation
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In materials science, a dislocation is a crystallographic defect or irregularity within a crystal structure. The presence of dislocations strongly influences many of the properties of materials, some types of dislocations can be visualized as being caused by the termination of a plane of atoms in the middle of a crystal. In such a case, the planes are not straight. The two primary types of dislocations are edge dislocations and screw dislocations, mixed dislocations are intermediate between these. Mathematically, dislocations are a type of defect, sometimes called a soliton. Dislocations behave as stable particles, they can move around, two dislocations of opposite orientation can cancel when brought together, but a single dislocation typically cannot disappear on its own. Two main types of dislocations exist, edge and screw, dislocations found in real materials are typically mixed, meaning that they have characteristics of both. A crystalline material consists of an array of atoms, arranged into lattice planes. One approach is to begin by considering a 3D representation of a crystal lattice. The viewer may then start to simplify the representation by visualising planes of atoms instead of the atoms themselves, an edge dislocation is a defect where an extra half-plane of atoms is introduced mid way through the crystal, distorting nearby planes of atoms. When enough force is applied from one side of the crystal structure, a simple schematic diagram of such atomic planes can be used to illustrate lattice defects such as dislocations. In an edge dislocation, the Burgers vector is perpendicular to the line direction, the stresses caused by an edge dislocation are complex due to its inherent asymmetry. A screw dislocation is much harder to visualize, imagine cutting a crystal along a plane and slipping one half across the other by a lattice vector, the halves fitting back together without leaving a defect. This is similar to the Riemann surface of the complex logarithm, if the cut only goes part way through the crystal, and then slipped, the boundary of the cut is a screw dislocation. It comprises a structure in which a path is traced around the linear defect by the atomic planes in the crystal lattice. Perhaps the closest analogy is a spiral-sliced ham, in pure screw dislocations, the Burgers vector is parallel to the line direction. Despite the difficulty in visualization, the caused by a screw dislocation are less complex than those of an edge dislocation. This equation suggests a long cylinder of stress radiating outward from the cylinder, please note, this simple model results in an infinite value for the core of the dislocation at r=0 and so it is only valid for stresses outside of the core of the dislocation
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Martensite
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It includes a class of hard minerals occurring as lath- or plate-shaped crystal grains. When viewed in section, the lenticular crystal grains may be incorrectly described as acicular. Austenite is γ-Fe, a solution of iron and alloying elements. As a result of the quenching, the cubic austenite transforms to a highly strained body-centered tetragonal form called martensite that is supersaturated with carbon. The shear deformations that result produce a number of dislocations. The highest hardness of a steel is 400 Brinell whereas martensite can achieve 700 Brinell. The martensitic reaction begins during cooling when the austenite reaches the start temperature. For a eutectoid steel, between 6 and 10% of austenite, called retained austenite, will remain. The percentage of retained austenite increases from insignificant for less than 0. 6% C steel, to 13% retained austenite at 0. 95% C, a very rapid quench is essential to create martensite. For steel 0-0. 6% carbon the martensite has the appearance of lath, for steel greater than 1% carbon it will form a plate like structure called plate martensite. Between those two percentages, the appearance of the grains is a mix of the two. The strength of the martensite is reduced as the amount of retained austenite grows, the process produces dislocation densities up to 1013/cm2. The great number of dislocations, combined with precipitates that originate and pin the dislocations in place, thus, martensite can be thermally induced or stress induced. One of the differences between the two phases is that martensite has a tetragonal crystal structure, whereas austenite has a face-centered cubic structure. Martensite has a lower density than austenite, so that the martensitic transformation results in a change of volume. Of considerably greater importance than the change is the shear strain which has a magnitude of about 0.26. Martensite is not shown in the phase diagram of the iron-carbon system because it is not an equilibrium phase. Equilibrium phases form by slow cooling rates that allow sufficient time for diffusion, since chemical processes accelerate at higher temperature, martensite is easily destroyed by the application of heat
39.
Nickel titanium
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Nickel titanium, also known as Nitinol, is a metal alloy of nickel and titanium, where the two elements are present in roughly equal atomic percentages e. g. Nitinol 55, Nitinol 60. Nitinol alloys exhibit two closely related and unique properties, shape memory effect and superelasticity, Shape memory is the ability of nitinol to undergo deformation at one temperature, then recover its original, undeformed shape upon heating above its transformation temperature. The word Nitinol is derived from its composition and its place of discovery, william J. Buehler along with Frederick Wang, discovered its properties during research at the Naval Ordnance Laboratory in 1959. Buehler was attempting to make a better missile nose cone, which could resist fatigue, heat, having found that a 1,1 alloy of nickel and titanium could do the job, in 1961 he presented a sample at a laboratory management meeting. The sample, folded up like an accordion, was passed around, one of them applied heat from his pipe lighter to the sample and, to everyones surprise, the accordion-shaped strip stretched and took its previous shape. While the potential applications for nitinol were realized immediately, practical efforts to commercialize the alloy did not take place until a decade later and this delay was largely because of the extraordinary difficulty of melting, processing and machining the alloy. Even these efforts encountered financial challenges that were not readily overcome until the 1980s, the discovery of the shape-memory effect in general dates back to 1932, when Swedish chemist Arne Ölander first observed the property in gold-cadmium alloys. The same effect was observed in Cu-Zn in the early 1950s, at high temperatures, nitinol assumes an interpenetrating simple cubic structure referred to as austenite. At low temperatures, nitinol spontaneously transforms to a more complicated crystal structure known as martensite. There are four transition temperatures associated to the austenite-to-martensite and martensite-to-austenite transformations, when the alloy is fully martensite and is subjected to heating, austenite starts to form at the austenite start temperature, As, and finishes at the austenite finish temperature, Af. The cooling/heating cycle shows thermal hysteresis, the hysteresis width depends on the precise nitinol composition and processing. Its typical value is a range spanning about 20-50 K. Crucial to nitinol properties are two key aspects of this phase transformation, first is that the transformation is reversible, meaning that heating above the transformation temperature will revert the crystal structure to the simpler austenite phase. The second key point is that the transformation in both directions is instantaneous, martensites crystal structure has the unique ability to undergo limited deformation in some ways without breaking atomic bonds. This type of deformation is known as twinning, which consists of the rearrangement of atomic planes without causing slip and it is able to undergo about 6–8% strain in this manner. When martensite is reverted to austenite by heating, the austenitic structure is restored. Thus the name shape memory refers to the fact that the shape of the high temperature austenite phase is remembered, even though the alloy is severely deformed at a lower temperature. A great deal of pressure can be produced by preventing the reversion of deformed martensite to austenite — from 35,000 psi to, in many cases, more than 100,000 psi
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Quenching
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In materials science, quenching is the rapid cooling of a workpiece to obtain certain material properties. A type of heat treating, quenching prevents undesired low-temperature processes, such as phase transformations, in steel alloyed with metals such as nickel and manganese, the eutectoid temperature becomes much lower, but the kinetic barriers to phase transformation remain the same. This allows quenching to start at a temperature, making the process much easier. High speed steel also has added tungsten, which serves to raise kinetic barriers, even cooling such alloys slowly in air has most of the desired effects of quenching. Extremely rapid cooling can prevent the formation of all crystal structure, if the percentage of carbon is less than 0.4 percent, quenching is not possible. Quench hardening is a process in which steel and cast iron alloys are strengthened and hardened. These metals consist of metals and alloys. This is done by heating the material to a certain temperature and this produces a harder material by either surface hardening or through-hardening varying on the rate at which the material is cooled. The material is often tempered to reduce the brittleness that may increase from the quench hardening process. Items that may be quenched include gears, shafts, and wear blocks, pearlite is not an ideal material for many common applications of steel alloys, as it is quite soft. Steels with this Martensitic structure are used in applications when the workpiece must be highly resistant to deformation. The process of quenching is a progression, beginning with heating the sample, most materials are heated to between 815 and 900 °C, with careful attention paid to keeping temperatures throughout the workpiece uniform. Minimizing uneven heating and overheating is key to imparting desired material properties, the second step in the quenching process is soaking. Workpieces can be soaked in air, a bath, or a vacuum. The recommended time allocation in salt or lead baths is up to 6 minutes, soaking times can range a little higher within a vacuum. As in the step, it is important that the temperature throughout the sample remains as uniform as possible during soaking. Once the workpiece has finished soaking, it moves on to the cooling step, during this step, the part is submerged into some kind of quenching fluid, different quenching fluids can have a significant effect on the final characteristics of a quenched part. Water is one of the most efficient quenching media where maximum hardness is desired, when hardness can be sacrificed, mineral oils are often used
41.
Steel
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Steel is an alloy of iron and other elements, primarily carbon, that is widely used in construction and other applications because of its high tensile strength and low cost. Steels base metal is iron, which is able to take on two forms, body centered cubic and face centered cubic, depending on its temperature. It is the interaction of those allotropes with the elements, primarily carbon. In the body-centred cubic arrangement, there is an atom in the centre of each cube. Carbon, other elements, and inclusions within iron act as hardening agents that prevent the movement of dislocations that otherwise occur in the lattices of iron atoms. The carbon in steel alloys may contribute up to 2. 1% of its weight. Steels strength compared to pure iron is possible at the expense of irons ductility. With the invention of the Bessemer process in the mid-19th century and this was followed by Siemens-Martin process and then Gilchrist-Thomas process that refined the quality of steel. With their introductions, mild steel replaced wrought iron, further refinements in the process, such as basic oxygen steelmaking, largely replaced earlier methods by further lowering the cost of production and increasing the quality of the product. Today, steel is one of the most common materials in the world and it is a major component in buildings, infrastructure, tools, ships, automobiles, machines, appliances, and weapons. Modern steel is generally identified by various grades defined by assorted standards organizations, the noun steel originates from the Proto-Germanic adjective stakhlijan, which is related to stakhla. The carbon content of steel is between 0. 002% and 2. 1% by weight for plain iron–carbon alloys and these values vary depending on alloying elements such as manganese, chromium, nickel, iron, tungsten, carbon and so on. Basically, steel is an alloy that does not undergo eutectic reaction. In contrast, cast iron does undergo eutectic reaction, too little carbon content leaves iron quite soft, ductile, and weak. Carbon contents higher than those of steel make an alloy, commonly called pig iron, while iron alloyed with carbon is called carbon steel, alloy steel is steel to which other alloying elements have been intentionally added to modify the characteristics of steel. Common alloying elements include, manganese, nickel, chromium, molybdenum, boron, titanium, vanadium, tungsten, cobalt, and niobium. Additional elements are important in steel, phosphorus, sulfur, silicon, and traces of oxygen, nitrogen, and copper. Alloys with a higher than 2. 1% carbon content, depending on other element content, cast iron is not malleable even when hot, but it can be formed by casting as it has a lower melting point than steel and good castability properties
42.
Body-centered cubic
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In crystallography, the cubic crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals, there are three main varieties of these crystals, Primitive cubic Body-centered cubic, Face-centered cubic Each is subdivided into other variants listed below. Note that although the cell in these crystals is conventionally taken to be a cube. This is related to the fact that in most cubic crystal systems, a classic isometric crystal has square or pentagonal faces. The three Bravais lattices in the crystal system are, The primitive cubic system consists of one lattice point on each corner of the cube. Each atom at a point is then shared equally between eight adjacent cubes, and the unit cell therefore contains in total one atom. The body-centered cubic system has one point in the center of the unit cell in addition to the eight corner points. It has a net total of 2 lattice points per unit cell, Each sphere in a cF lattice has coordination number 12. The face-centered cubic system is related to the hexagonal close packed system. The plane of a cubic system is a hexagonal grid. Attempting to create a C-centered cubic crystal system would result in a simple tetragonal Bravais lattice, there are a total 36 cubic space groups. Other terms for hexoctahedral are, normal class, holohedral, ditesseral central class, a simple cubic unit cell has a single cubic void in the center. Additionally, there are 24 tetrahedral voids located in a square spacing around each octahedral void and these tetrahedral voids are not local maxima and are not technically voids, but they do occasionally appear in multi-atom unit cells. A face-centered cubic unit cell has eight tetrahedral voids located midway between each corner and the center of the cell, for a total of eight net tetrahedral voids. One important characteristic of a structure is its atomic packing factor. This is calculated by assuming all the atoms are identical spheres. The atomic packing factor is the proportion of space filled by these spheres, assuming one atom per lattice point, in a primitive cubic lattice with cube side length a, the sphere radius would be a⁄2 and the atomic packing factor turns out to be about 0.524. Similarly, in a bcc lattice, the atomic packing factor is 0.680, as a rule, since atoms in a solid attract each other, the more tightly packed arrangements of atoms tend to be more common
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Close-packing of equal spheres
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In geometry, close-packing of equal spheres is a dense arrangement of congruent spheres in an infinite, regular arrangement. Carl Friedrich Gauss proved that the highest average density – that is, the same packing density can also be achieved by alternate stackings of the same close-packed planes of spheres, including structures that are aperiodic in the stacking direction. The Kepler conjecture states that this is the highest density that can be achieved by any arrangement of spheres and this conjecture was proven by T. C. Highest density is only in case of 1,2,3,8 and 24 dimensions. Many crystal structures are based on a close-packing of a kind of atom. The cubic and hexagonal arrangements are very close to one another in energy, there are two simple regular lattices that achieve this highest average density. They are called face-centered cubic and hexagonal close-packed, based on their symmetry, both are based upon sheets of spheres arranged at the vertices of a triangular tiling, they differ in how the sheets are stacked upon one another. The fcc lattice is known to mathematicians as that generated by the A3 root system. Cannonballs were usually piled in a rectangular or triangular wooden frame, both arrangements produce a face-centered cubic lattice – with different orientation to the ground. Hexagonal close-packing would result in a pyramid with a hexagonal base. In both the fcc and hcp arrangements each sphere has twelve neighbors, for every sphere there is one gap surrounded by six spheres and two smaller gaps surrounded by four spheres. The distances to the centers of these gaps from the centers of the spheres is √ 3⁄2 for the tetrahedral, and √2 for the octahedral. Relative to a layer with positioning A, two more positionings B and C are possible. Every sequence of A, B, and C without immediate repetition of the one is possible. The most regular ones are fcc = ABCABCA hcp = ABABABA, in close-packing, the center-to-center spacing of spheres in the xy plane is a simple honeycomb-like tessellation with a pitch of one sphere diameter. The coordination number of hcp and fcc is 12 and their atomic packing factors are equal to the mentioned above,0.74. The distance between the centers along the shortest path namely that straight line will therefore be r1 + r2 where r1 is the radius of the first sphere, in close packing all of the spheres share a common radius, r. Therefore two centers would simply have a distance 2r, hexagonal close packing of spheres, the coordinate points of the lattice will be the spheres centers
44.
Stacking-fault energy
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The stacking-fault energy is a materials property on a very small scale. It is noted as γSFE in units of energy per area, stacking-fault energy is a primary factor in determining the wear resistance of a metal and, primarily, its resistance to galling. A stacking fault is an interruption of the stacking sequence of atomic planes in a crystal structure. These interruptions carry a certain stacking-fault energy, the equilibrium width is thus partially determined by the stacking-fault energy. When the SFE is high the dissociation of a full dislocation into two partials is energetically unfavorable, and the material deforms only by dislocation glide, lower SFE materials display wider stacking faults and have more difficulties for cross-slip and climb. The SFE modifies the ability of a dislocation in a crystal to glide onto a slip plane. When the SFE is low, the mobility of dislocations in a material decreases and these irregularities carry a certain energy which is called stacking-fault energy. Stacking fault energy is heavily influenced by a few factors, specifically base metal, alloying metals, percent of alloy metals. It has long established that the addition of alloying elements significantly lowers the SFE of most metals. Which element and how much is added dramatically affects the SFE of a material, the figures on the right show how the SFE of copper lowers with the addition of two different alloying elements, zinc and aluminum. In both cases, the SFE of the brass decreases with increasing alloy content, however, the SFE of the Cu-Al alloy decreases faster and reaches a lower minimum. Another factor that has a significant effect on the SFE of a material and is very interrelated with alloy content is the e/a ratio, thornton showed this in 1962 by plotting the e/a ratio vs SFE for a few Cu based alloys. He found that the valence-electron to atom ratio is a predictor of stacking fault energy. This directly supports the graphs on the right, zinc is a heavier element and only has two valence electrons, whereas aluminum is lighter and has three valence electrons. Thus each weight percent of aluminum has a greater impact on the SFE of the Cu-based alloy than does zinc. The two primary methods of deformation in metals are slip and twinning, slip occurs by dislocation glide of either screw or edge dislocations within a slip plane. Slip is by far the most common mechanism, twinning is less common but readily occurs under some circumstances. Twinning occurs when there are not enough slip systems to accommodate deformation and/or when the material has a very low SFE, twins are abundant in many low SFE metals like copper alloys, but are rarely seen in high SFE metals like aluminum
45.
Icosahedral twins
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An icosahedral twin is a twenty-face cluster made of ten interlinked dual-tetrahedron crystals, typically joined along triangular faces having three-fold symmetry. One can think of their formation as a kind of nano-scale self-assembly, a variety of nanostructures assume icosahedral form on size scales where surface forces eclipse those from the bulk. A twinned-form of these nanostructures is sometimes found to occur e. g. in face-centered-cubic metal-atom clusters larger than 10 nm in diameter. This may occur when the building-blocks beneath each of the 20 facets of an initially icosahedral cluster make the case for conversion to a translationally symmetric crystalline form. When interatom bonding does not have strong directional preferences, it is not unusual for atoms to gravitate toward a number of 12 nearest neighbors. The three most symmetric ways to do this are by icosahedral clustering, or by crystalline face-centered-cubic and/or hexagonal close packing. Icosahedral arrangements, perhaps because of their slightly smaller area, may be preferred for small clusters e. g. noble gas. However, the Achilles heel for icosahedral clustering about a point is that it cannot fill space over large distances in a way that is translationally ordered. Hence bulk atoms generally revert to one of the crystalline close-packing configurations instead, thus icosahedral twins are born, with a certain amount of strain along the interfacial planes. Icosahedral-twinning has been seen in face-centered-cubic metal-nanoparticles that have nucleated, by evaporation onto surfaces, out of solution, icosahedral twinning seems to be the result when clusters growing outward from an icoashedral-seed get larger than about 10 in diameter. Quasicrystals are un-twinned structures with long range rotational but not translational periodicity, quasi-crystals let non-space-filling coordination persist to larger size scales. However, they form only when the compositional makeup serves as an antagonist to formation of one of the more common close-packed space-filling. Face-centered-cubic noble-metal atom-clusters are important chemical-reaction nano-catalysts, one example of this is the platinum used in automobile catalytic converters. Icosahedral twinning makes it possible to cover the surface of a nanoparticle with facets. Electron diffraction and high-resolution transmission electron microscope imaging are two methods for identifying the structure of individual clusters. Digital darkfield analysis of images shows promise for recognition of icosahedral twinning from most of the randomly oriented clusters in a microscope-image field of view. Nanotechnology Nanomaterial based catalyst Crystal twinning Self-assembly of nanoparticles Icosahedron Quasicrystals Dark field microscopy
Spencer, Leonard James (1911). "Crystallography". Encyclopædia Britannica. 7 (11th ed.). pp. 569–591. 
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Spencer, Leonard James (1911). "
This article incorporates text from this source, which is in the