1.
Forsterite
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Forsterite is the magnesium-rich end-member of the olivine solid solution series. It is isomorphous with the iron-rich end-member, fayalite, forsterite crystallizes in the orthorhombic system with cell parameters a 4.75 Å, b 10.20 Å and c 5.98 Å. Forsterite is associated with igneous and metamorphic rocks and has also found in meteorites. In 2005 it was found in cometary dust returned by the Stardust probe. In 2011 it was observed as tiny crystals in the dusty clouds of gas around a forming star, two polymorphs of forsterite are known, wadsleyite and ringwoodite. Both are mainly known from meteorites, peridot is the gemstone variety of forsterite olivine. Forsterite reacts with quartz to form the orthopyroxene mineral enstatite in the following reaction, pure forsterite is composed of magnesium, oxygen and silicon. Other minerals such as monticellite, an uncommon mineral, share the olivine structure. Monticellite is found in contact metamorphosed dolomites, forsterite-rich olivine is the most abundant mineral in the mantle above a depth of about 400 km, pyroxenes are also important minerals in this upper part of the mantle. Due to its melting point, olivine crystals are the first minerals to precipitate from a magmatic melt in a cumulate process. Forsterite-rich olivine is a common product of mantle-derived magma. Olivine in mafic and ultramafic rocks typically is rich in the forsterite end-member, forsterite also occurs in dolomitic marble which results from the metamorphism of high magnesium limestones and dolostones. Nearly pure forsterite occurs in some metamorphosed serpentinites, fayalite-rich olivine is much less common. Nearly pure fayalite is a constituent in some granite-like rocks. Forsterite is mainly composed of the anion SiO44− and the cation Mg2+ in a molar ratio 1,2, silicon is the central atom in the SiO44− anion. Each oxygen atom is bonded to the silicon by a covalent bond. The four oxygen atoms have a negative charge because of the covalent bond with silicon. Therefore, oxygen atoms need to stay far from other in order to reduce the repulsive force between them
2.
Silicate mineral
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Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of rock-forming minerals and they are classified based on the structure of their silicate groups, which contain different ratios of silicon and oxygen. Nesosilicates, or orthosilicates, have the orthosilicate ion, which constitute isolated 4− tetrahedra that are connected only by interstitial cations and these exist as 3-member 6− and 6-member 12− rings, where T stands for a tetrahedrally coordinated cation. Inosilicates, or chain silicates, have interlocking chains of silicate tetrahedra with either SiO3,1,3 ratio, for single chains or Si4O11,4,11 ratio, for double chains. Nickel–Strunz classification,09. D Pyroxene group Enstatite – orthoferrosilite series Enstatite – MgSiO3 Ferrosilite – FeSiO3 Pigeonite – Ca0.251, all phyllosilicate minerals are hydrated, with either water or hydroxyl groups attached. Serpentine subgroup Antigorite – Mg3Si2O54 Chrysotile – Mg3Si2O54 Lizardite – Mg3Si2O54 Clay minerals group Halloysite – Al2Si2O54 Kaolinite – Al2Si2O54 Illite – 24O10 Montmorillonite –0 and this group comprises nearly 75% of the crust of the Earth. Tectosilicates, with the exception of the group, are aluminosilicates. Nickel–Strunz classification,09. F and 09. G,04. A, an introduction to the rock-forming minerals. Wise, W. S. Zussman, J. Rock-forming minerals, P.982 pp. Hurlbut, Cornelius S. Danas Manual of Mineralogy. Mindat. org, Dana classification Webmineral, Danas New Silicate Classification Media related to Silicates at Wikimedia Commons
3.
Chemical formula
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These are limited to a single typographic line of symbols, which may include subscripts and superscripts. A chemical formula is not a name, and it contains no words. Although a chemical formula may imply certain simple chemical structures, it is not the same as a full chemical structural formula. Chemical formulas can fully specify the structure of only the simplest of molecules and chemical substances, the simplest types of chemical formulas are called empirical formulas, which use letters and numbers indicating the numerical proportions of atoms of each type. Molecular formulas indicate the numbers of each type of atom in a molecule. For example, the formula for glucose is CH2O, while its molecular formula is C6H12O6. This is possible if the relevant bonding is easy to show in one dimension, an example is the condensed molecular/chemical formula for ethanol, which is CH3-CH2-OH or CH3CH2OH. For reasons of structural complexity, there is no condensed chemical formula that specifies glucose, chemical formulas may be used in chemical equations to describe chemical reactions and other chemical transformations, such as the dissolving of ionic compounds into solution. A chemical formula identifies each constituent element by its chemical symbol, in empirical formulas, these proportions begin with a key element and then assign numbers of atoms of the other elements in the compound, as ratios to the key element. For molecular compounds, these numbers can all be expressed as whole numbers. For example, the formula of ethanol may be written C2H6O because the molecules of ethanol all contain two carbon atoms, six hydrogen atoms, and one oxygen atom. Some types of compounds, however, cannot be written with entirely whole-number empirical formulas. An example is boron carbide, whose formula of CBn is a variable non-whole number ratio with n ranging from over 4 to more than 6.5. When the chemical compound of the consists of simple molecules. These types of formulas are known as molecular formulas and condensed formulas. A molecular formula enumerates the number of atoms to reflect those in the molecule, so that the formula for glucose is C6H12O6 rather than the glucose empirical formula. However, except for very simple substances, molecular chemical formulas lack needed structural information, for simple molecules, a condensed formula is a type of chemical formula that may fully imply a correct structural formula. For example, ethanol may be represented by the chemical formula CH3CH2OH
4.
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
5.
Monoclinic crystal system
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In crystallography, the monoclinic crystal system is one of the 7 crystal systems. A crystal system is described by three vectors, in the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic system. They form a rectangular prism with a parallelogram as its base, hence two vectors are perpendicular, while the third vector meets the other two at an angle other than 90°. There is only one monoclinic Bravais lattice in two dimensions, the oblique lattice, two monoclinic Bravais lattices exist, the primitive monoclinic and the centered monoclinic lattices. In this axis setting, the primitive and base-centered lattices interchange in centering type, sphenoidal is also monoclinic hemimorphic, Domatic is also monoclinic hemihedral, Prismatic is also monoclinic normal. Crystal structure Hurlbut, Cornelius S. Klein, Cornelis, hahn, Theo, ed. International Tables for Crystallography, Volume A, Space Group Symmetry
6.
Triclinic crystal system
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In crystallography, the triclinic crystal system is one of the 7 crystal systems. A crystal system is described by three basis vectors, in the triclinic system, the crystal is described by vectors of unequal length, as in the orthorhombic system. In addition, no vector is at right angles orthogonal to another, the triclinic lattice is the least symmetric of the 14 three-dimensional Bravais lattices. It is the lattice type that itself has no mirror planes. There are a total 2 space groups, with each only one space group is associated. Pinacoidal is also known as triclinic normal, pedial is also triclinic hemihedral Mineral examples include plagioclase, microcline, rhodonite, turquoise, wollastonite and amblygonite, all in triclinic normal. Crystal structure Hurlbut, Cornelius S. Klein, Cornelis,1985, Manual of Mineralogy, 20th ed. pp.64 –65, ISBN 0-471-80580-7
7.
Crystallographic point group
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For a periodic crystal, the group must also be consistent with maintenance of the three-dimensional translational symmetry that defines crystallinity. The macroscopic properties of a crystal would look exactly the same before, in the classification of crystals, each point group is also known as a crystal class. There are infinitely many three-dimensional point groups, however, the crystallographic restriction of the infinite families of general point groups results in there being only 32 crystallographic point groups. These 32 point groups are one-and-the same as the 32 types of morphological crystalline symmetries derived in 1830 by Johann Friedrich Christian Hessel from a consideration of observed crystal forms, the point groups are denoted by their component symmetries. There are a few standard notations used by crystallographers, mineralogists, for the correspondence of the two systems below, see crystal system. In Schoenflies notation, point groups are denoted by a symbol with a subscript. The symbols used in crystallography mean the following, Cn indicates that the group has a rotation axis. Cnh is Cn with the addition of a plane perpendicular to the axis of rotation. Cnv is Cn with the addition of n mirror planes parallel to the axis of rotation, s2n denotes a group that contains only a 2n-fold rotation-reflection axis. Dn indicates that the group has a rotation axis plus n twofold axes perpendicular to that axis. Dnh has, in addition, a plane perpendicular to the n-fold axis. Dnd has, in addition to the elements of Dn, mirror planes parallel to the n-fold axis, the letter T indicates that the group has the symmetry of a tetrahedron. Td includes improper rotation operations, T excludes improper rotation operations, the letter O indicates that the group has the symmetry of an octahedron, with or without improper operations. Due to the crystallographic restriction theorem, n =1,2,3,4, d4d and D6d are actually forbidden because they contain improper rotations with n=8 and 12 respectively. The 27 point groups in the table plus T, Td, Th, O, an abbreviated form of the Hermann–Mauguin notation commonly used for space groups also serves to describe crystallographic point groups. Group names are Molecular symmetry Point group Space group Point groups in three dimensions Crystal system Point-group symbols in International Tables for Crystallography,12.1, pp. 818-820 Names and symbols of the 32 crystal classes in International Tables for Crystallography. 10.1, p.794 Pictorial overview of the 32 groups Point Groups - Flow Chart Inorganic Chemistry Group Theory Practice Problems
8.
Crystal structure
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In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material. Ordered structures occur from the nature of the constituent particles to form symmetric patterns that repeat along the principal directions of three-dimensional space in matter. The smallest group of particles in the material that constitutes the pattern is the unit cell of the structure. The unit cell completely defines the symmetry and structure of the crystal lattice. The repeating patterns are said to be located at the points of the Bravais lattice, the lengths of the principal axes, or edges, of the unit cell and the angles between them are the lattice constants, also called lattice parameters. The symmetry properties of the crystal are described by the concept of space groups, all possible symmetric arrangements of particles in three-dimensional space may be described by the 230 space groups. The crystal structure and symmetry play a role in determining many physical properties, such as cleavage, electronic band structure. The crystal structure of a material can be described in terms of its unit cell, the unit cell is a box containing one or more atoms arranged in three dimensions. The unit cells stacked in three-dimensional space describe the arrangement of atoms of the crystal. Commonly, atomic positions are represented in terms of fractional coordinates, the atom positions within the unit cell can be calculated through application of symmetry operations to the asymmetric unit. The asymmetric unit refers to the smallest possible occupation of space within the unit cell and this does not, however imply that the entirety of the asymmetric unit must lie within the boundaries of the unit cell. Symmetric transformations of atom positions are calculated from the group of the crystal structure. Vectors and planes in a lattice are described by the three-value Miller index notation. It uses the indices ℓ, m, and n as directional parameters, which are separated by 90°, by definition, the syntax denotes a plane that intercepts the three points a1/ℓ, a2/m, and a3/n, or some multiple thereof. That is, the Miller indices are proportional to the inverses of the intercepts of the plane with the unit cell, if one or more of the indices is zero, it means that the planes do not intersect that axis. A plane containing a coordinate axis is translated so that it no longer contains that axis before its Miller indices are determined, the Miller indices for a plane are integers with no common factors. Negative indices are indicated with horizontal bars, as in, in an orthogonal coordinate system for a cubic cell, the Miller indices of a plane are the Cartesian components of a vector normal to the plane. Likewise, the planes are geometric planes linking nodes
9.
Crystal habit
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In mineralogy, crystal habit is the characteristic external shape of an individual crystal or crystal group. A single crystals habit is a description of its shape and its crystallographic forms. Recognizing the habit may help in identifying a mineral, when the faces are well-developed due to uncrowded growth a crystal is called euhedral, one with partially developed faces is subhedral, and one with undeveloped crystal faces is called anhedral. The long axis of a quartz crystal typically has a six-sided prismatic habit with parallel opposite faces. Aggregates can be formed of individual crystals with euhedral to anhedral grains, the arrangement of crystals within the aggregate can be characteristic of certain minerals. For example, minerals used for asbestos insulation often grow in a fibrous habit, the terms used by mineralogists to report crystal habits describe the typical appearance of an ideal mineral. Recognizing the habit can aid in identification as some habits are characteristic, most minerals, however, do not display ideal habits due to conditions during crystallization. Minerals belonging to the crystal system do not necessarily exhibit the same habit. Some habits of a mineral are unique to its variety and locality, For example, while most sapphires form elongate barrel-shaped crystals, ordinarily, the latter habit is seen only in ruby. Sapphire and ruby are both varieties of the mineral, corundum. Some minerals may replace other existing minerals while preserving the originals habit, a classic example is tigers eye quartz, crocidolite asbestos replaced by silica. While quartz typically forms prismatic crystals, in tigers eye the original fibrous habit of crocidolite is preserved, the names of crystal habits are derived from, Predominant crystal faces. Abnormal grain growth Grain growth Crystallization
10.
Cleavage (crystal)
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Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite crystallographic structural planes. Cleavage forms parallel to planes, Basal or pinacoidal cleavage occurs when there is only one cleavage plane. Mica also has basal cleavage, this is why mica can be peeled into thin sheets, cubic cleavage occurs on when there are three cleavage planes intersecting at 90 degrees. Halite has cubic cleavage, and therefore, when halite crystals are broken, octahedral cleavage occurs when there are four cleavage planes in a crystal. Octahedral cleavage is common for semiconductors, rhombohedral cleavage occurs when there are three cleavage planes intersecting at angles that are not 90 degrees. Prismatic cleavage occurs when there are two planes in a crystal. Dodecahedral cleavage occurs when there are six cleavage planes in a crystal, crystal parting occurs when minerals break along planes of structural weakness due to external stress or along twin composition planes. Parting breaks are very similar in appearance to cleavage, but only due to stress. Examples include magnetite which shows octahedral parting, the parting of corundum. Cleavage is a property traditionally used in mineral identification, both in hand specimen and microscopic examination of rock and mineral studies. As an example, the angles between the cleavage planes for the pyroxenes and the amphiboles are diagnostic. Crystal cleavage is of importance in the electronics industry and in the cutting of gemstones. Precious stones are generally cleaved by impact, as in diamond cutting, synthetic single crystals of semiconductor materials are generally sold as thin wafers which are much easier to cleave. Elemental semiconductors are diamond cubic, a group for which octahedral cleavage is observed. This means that some orientations of wafer allow near-perfect rectangles to be cleaved, most other commercial semiconductors can be made in the related zinc blende structure, with similar cleavage planes. Cleavage Mineral galleries, Mineral properties – Cleavage
11.
Fracture (mineralogy)
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In the field of mineralogy, fracture is the texture and shape of a rocks surface formed when a mineral is fractured. Minerals often have a highly distinctive fracture, making it a feature used in their identification. Fracture differs from cleavage in that the latter involves clean splitting along the planes of the minerals crystal structure. All minerals exhibit fracture, but when very strong cleavage is present, conchoidal fracture breakage that resembles the concentric ripples of a mussel shell. It often occurs in amorphous or fine-grained minerals such as flint, opal or obsidian, subconchoidal fracture is similar to conchoidal fracture, but with less significant curvature. Earthy fracture is reminiscent of freshly broken soil and it is frequently seen in relatively soft, loosely bound minerals, such as limonite, kaolinite and aluminite. Hackly fracture is jagged, sharp and not even and it occurs when metals are torn, and so is often encountered in native metals such as copper and silver. Splintery fracture comprises sharp elongated points and it is particularly seen in fibrous minerals such as chrysotile, but may also occur in non-fibrous minerals such as kyanite. Uneven fracture is a surface or one with random irregularities. It occurs in a range of minerals including arsenopyrite, pyrite and magnetite. Rudolf Duda and Lubos Rejl, Minerals of the World http, //www. galleries. com/minerals/property/fracture. htm
12.
Mohs scale of mineral hardness
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The Mohs scale of mineral hardness is a qualitative ordinal scale characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. Created in 1812 by German geologist and mineralogist Friedrich Mohs, it is one of several definitions of hardness in materials science, while greatly facilitating the identification of minerals in the field, the Mohs scale does not show how well hard materials perform in an industrial setting. Despite its lack of precision, the Mohs scale is highly relevant for field geologists, the Mohs scale hardness of minerals can be commonly found in reference sheets. Reference materials may be expected to have a uniform Mohs hardness, the Mohs scale of mineral hardness is based on the ability of one natural sample of mineral to scratch another mineral visibly. The samples of matter used by Mohs are all different minerals, Minerals are pure substances found in nature. Rocks are made up of one or more minerals, as the hardest known naturally occurring substance when the scale was designed, diamonds are at the top of the scale. The hardness of a material is measured against the scale by finding the hardest material that the material can scratch. For example, if material is scratched by apatite but not by fluorite. Scratching a material for the purposes of the Mohs scale means creating non-elastic dislocations visible to the naked eye, frequently, materials that are lower on the Mohs scale can create microscopic, non-elastic dislocations on materials that have a higher Mohs number. The Mohs scale is an ordinal scale. For example, corundum is twice as hard as topaz, the table below shows the comparison with the absolute hardness measured by a sclerometer, with pictorial examples. On the Mohs scale, a streak plate has a hardness of 7.0, using these ordinary materials of known hardness can be a simple way to approximate the position of a mineral on the scale. The table below incorporates additional substances that may fall between levels, Comparison between Hardness and Hardness, Mohs hardness of elements is taken from G. V, samsonov in Handbook of the physicochemical properties of the elements, IFI-Plenum, New York, USA,1968. The Hardness of Minerals and Rocks
13.
Lustre (mineralogy)
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Lustre or luster is the way light interacts with the surface of a crystal, rock, or mineral. The word traces its origins back to the latin lux, meaning light, a range of terms are used to describe lustre, such as earthy, metallic, greasy, and silky. Similarly, the term refers to a glassy lustre. A list of terms is given below. Lustre varies over a continuum, and so there are no rigid boundaries between the different types of lustre. The terms are frequently combined to describe types of lustre. Some minerals exhibit unusual optical phenomena, such as asterism or chatoyancy, a list of such phenomena is given below. Adamantine minerals possess a superlative lustre, which is most notably seen in diamond, such minerals are transparent or translucent, and have a high refractive index. Minerals with an adamantine lustre are uncommon, with examples being cerussite. Minerals with a degree of lustre are referred to as subadamantine, with some examples being garnet. Dull minerals exhibit little to no lustre, due to coarse granulations which scatter light in all directions, a distinction is sometimes drawn between dull minerals and earthy minerals, with the latter being coarser, and having even less lustre. Greasy minerals resemble fat or grease, a greasy lustre often occurs in minerals containing a great abundance of microscopic inclusions, with examples including opal and cordierite. Many minerals with a greasy lustre also feel greasy to the touch, metallic minerals have the lustre of polished metal, and with ideal surfaces will work as a reflective surface. Examples include galena, pyrite and magnetite, pearly minerals consist of thin transparent co-planar sheets. Light reflecting from these layers give them a lustre reminiscent of pearls, such minerals possess perfect cleavage, with examples including muscovite and stilbite. Resinous minerals have the appearance of resin, chewing gum or plastic, a principal example is amber, which is a form of fossilized resin. Silky minerals have an arrangement of extremely fine fibres, giving them a lustre reminiscent of silk. Examples include asbestos, ulexite and the satin spar variety of gypsum, a fibrous lustre is similar, but has a coarser texture
14.
Streak (mineralogy)
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The streak of a mineral is the color of the powder produced when it is dragged across an un-weathered surface. If no streak seems to be made, the streak is said to be white or colorless. Streak is particularly important as a diagnostic for opaque and colored materials and it is less useful for silicate minerals, most of which have a white streak or are too hard to powder easily. The apparent color of a mineral can vary widely because of impurities or a disturbed macroscopic crystal structure. Small amounts of an impurity that strongly absorbs a particular wavelength can radically change the wavelengths of light that are reflected by the specimen, and thus change the apparent color. However, when the specimen is dragged to produce a streak, it is broken into randomly oriented microscopic crystals, the surface across which the mineral is dragged is called a streak plate, and is generally made of unglazed porcelain tile. In the absence of a plate, the unglazed underside of a porcelain bowl or vase or the back of a glazed tile will work. Sometimes a streak is more easily or accurately described by comparing it with the streak made by another streak plate. Because the trail left behind results from the mineral being crushed into powder, in case of harder minerals, the color of the powder can be determined by filing or crushing with a hammer a small sample, which is then usually rubbed on a streak plate. Most minerals that are harder have a white streak. Some minerals leave a similar to their natural color, such as cinnabar. Other minerals leave surprising colors, such as fluorite, which always has a streak, although it can appear in purple, blue, yellow. Hematite, which is black in appearance, leaves a red streak which accounts for its name, galena, which can be similar in appearance to hematite, is easily distinguished by its gray streak. Hamilton, W. R. Cambridge Guide to Minerals, Rocks, the Encyclopedia of Gemstones and Minerals. New York, Facts on File. p.251, physical Characteristics of Minerals, at Introduction to Mineralogy by Andrea Bangert What is Streak
15.
Transparency and translucency
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In the field of optics, transparency is the physical property of allowing light to pass through the material without being scattered. On a macroscopic scale, the photons can be said to follow Snells Law, in other words, a translucent medium allows the transport of light while a transparent medium not only allows the transport of light but allows for image formation. The opposite property of translucency is opacity, transparent materials appear clear, with the overall appearance of one color, or any combination leading up to a brilliant spectrum of every color. When light encounters a material, it can interact with it in different ways. These interactions depend on the wavelength of the light and the nature of the material, photons interact with an object by some combination of reflection, absorption and transmission. Some materials, such as glass and clean water, transmit much of the light that falls on them and reflect little of it. Many liquids and aqueous solutions are highly transparent, absence of structural defects and molecular structure of most liquids are mostly responsible for excellent optical transmission. Materials which do not transmit light are called opaque, many such substances have a chemical composition which includes what are referred to as absorption centers. Many substances are selective in their absorption of light frequencies. They absorb certain portions of the spectrum while reflecting others. The frequencies of the spectrum which are not absorbed are either reflected or transmitted for our physical observation and this is what gives rise to color. The attenuation of light of all frequencies and wavelengths is due to the mechanisms of absorption. Transparency can provide almost perfect camouflage for animals able to achieve it and this is easier in dimly-lit or turbid seawater than in good illumination. Many marine animals such as jellyfish are highly transparent, at the atomic or molecular level, physical absorption in the infrared portion of the spectrum depends on the frequencies of atomic or molecular vibrations or chemical bonds, and on selection rules. Nitrogen and oxygen are not greenhouse gases because there is no absorption because there is no molecular dipole moment. With regard to the scattering of light, the most critical factor is the scale of any or all of these structural features relative to the wavelength of the light being scattered. Primary material considerations include, Crystalline structure, whether or not the atoms or molecules exhibit the long-range order evidenced in crystalline solids, glassy structure, scattering centers include fluctuations in density or composition. Microstructure, scattering centers include internal surfaces such as boundaries, crystallographic defects
16.
Specific gravity
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This page is about the measurement using water as a reference. For a general use of gravity, see relative density. See intensive property for the property implied by specific, Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is always water at its densest for liquids. Nonetheless, the temperature and pressure must be specified for both the sample and the reference, pressure is nearly always 1 atm. Temperatures for both sample and reference vary from industry to industry, in British beer brewing, the practice for specific gravity as specified above is to multiply it by 1000. Being a ratio of densities, specific gravity is a dimensionless quantity, Specific gravity varies with temperature and pressure, reference and sample must be compared at the same temperature and pressure or be corrected to a standard reference temperature and pressure. Substances with a gravity of 1 are neutrally buoyant in water. Those with SG greater than 1 are denser than water and will, disregarding surface tension effects and those with an SG less than 1 are less dense than water and will float on it. In scientific work, the relationship of mass to volume is expressed directly in terms of the density of the substance under study. It is in industry where specific gravity finds wide application, often for historical reasons. True specific gravity can be expressed mathematically as, S G true = ρ sample ρ H2 O where ρ sample is the density of the sample, the density of water varies with temperature and pressure as does the density of the sample. So it is necessary to specify the temperatures and pressures at which the densities or weights were determined and it is nearly always the case that measurements are made at 1 nominal atmosphere. For true specific gravity calculations, air pressure must be considered, temperatures are specified by the notation with T s representing the temperature at which the samples density was determined and T r the temperature at which the reference density is specified. For example, SG would be understood to mean that the density of the sample was determined at 20°C and of the water at 4°C. Taking into account different sample and reference temperatures, we note that, while S G H2 O =1.000000, it is also the case that S G H2 O =0.998203 /0.999840 =0.998363. Here, temperature is being specified using the current ITS-90 scale, on the previous IPTS-68 scale, the densities at 20 °C and 4 °C are 0.9982071 and 0.9999720 respectively, resulting in an SG value for water of 0.9982343. For example, in the industry, the Plato table lists sucrose concentration by weight against true SG
17.
Refractive index
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In optics, the refractive index or index of refraction n of a material is a dimensionless number that describes how light propagates through that medium. It is defined as n = c v, where c is the speed of light in vacuum, for example, the refractive index of water is 1.333, meaning that light travels 1.333 times faster in a vacuum than it does in water. The refractive index determines how light is bent, or refracted. The refractive indices also determine the amount of light that is reflected when reaching the interface, as well as the angle for total internal reflection. This implies that vacuum has a index of 1. The refractive index varies with the wavelength of light and this is called dispersion and causes the splitting of white light into its constituent colors in prisms and rainbows, and chromatic aberration in lenses. Light propagation in absorbing materials can be described using a refractive index. The imaginary part then handles the attenuation, while the real part accounts for refraction, the concept of refractive index is widely used within the full electromagnetic spectrum, from X-rays to radio waves. It can also be used with wave phenomena such as sound, in this case the speed of sound is used instead of that of light and a reference medium other than vacuum must be chosen. Thomas Young was presumably the person who first used, and invented, at the same time he changed this value of refractive power into a single number, instead of the traditional ratio of two numbers. The ratio had the disadvantage of different appearances, newton, who called it the proportion of the sines of incidence and refraction, wrote it as a ratio of two numbers, like 529 to 396. Hauksbee, who called it the ratio of refraction, wrote it as a ratio with a fixed numerator, hutton wrote it as a ratio with a fixed denominator, like 1.3358 to 1. Young did not use a symbol for the index of refraction, in the next years, others started using different symbols, n, m, and µ. For visible light most transparent media have refractive indices between 1 and 2, a few examples are given in the adjacent table. These values are measured at the yellow doublet D-line of sodium, with a wavelength of 589 nanometers, gases at atmospheric pressure have refractive indices close to 1 because of their low density. Almost all solids and liquids have refractive indices above 1.3, aerogel is a very low density solid that can be produced with refractive index in the range from 1.002 to 1.265. Moissanite lies at the end of the range with a refractive index as high as 2.65. Most plastics have refractive indices in the range from 1.3 to 1.7, for infrared light refractive indices can be considerably higher
18.
Birefringence
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Birefringence is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. These optically anisotropic materials are said to be birefringent, the birefringence is often quantified as the maximum difference between refractive indices exhibited by the material. Crystals with non-cubic crystal structures are often birefringent, as are plastics under mechanical stress and this effect was first described by the Danish scientist Rasmus Bartholin in 1669, who observed it in calcite, a crystal having one of the strongest birefringences. A mathematical description of wave propagation in a birefringent medium is presented below, following is a qualitative explanation of the phenomenon. Thus rotating the material around this axis does not change its optical behavior and this special direction is known as the optic axis of the material. Light whose polarization is perpendicular to the axis is governed by a refractive index no. Light whose polarization is in the direction of the optic axis sees an optical index ne, for any ray direction there is a linear polarization direction perpendicular to the optic axis, and this is called an ordinary ray. The magnitude of the difference is quantified by the birefringence, Δ n = n e − n o, the propagation of the ordinary ray is simply described by no as if there were no birefringence involved. However the extraordinary ray, as its name suggests, propagates unlike any wave in an optical material. Its refraction at a surface can be using the effective refractive index. However it is in fact an inhomogeneous wave whose power flow is not exactly in the direction of the wave vector and this causes an additional shift in that beam, even when launched at normal incidence, as is popularly observed using a crystal of calcite as photographed above. Rotating the calcite crystal will cause one of the two images, that of the ray, to rotate slightly around that of the ordinary ray. When the light propagates either along or orthogonal to the optic axis, in the first case, both polarizations see the same effective refractive index, so there is no extraordinary ray. In the second case the extraordinary ray propagates at a different phase velocity but is not an inhomogeneous wave, for instance, a quarter-wave plate is commonly used to create circular polarization from a linearly polarized source. The case of so-called biaxial crystals is substantially more complex and these are characterized by three refractive indices corresponding to three principal axes of the crystal. For most ray directions, both polarizations would be classified as extraordinary rays but with different effective refractive indices, being extraordinary waves, however, the direction of power flow is not identical to the direction of the wave vector in either case. The two refractive indices can be determined using the index ellipsoids for given directions of the polarization, note that for biaxial crystals the index ellipsoid will not be an ellipsoid of revolution but is described by three unequal principle refractive indices nα, nβ and nγ. Thus there is no axis around which a rotation leaves the optical properties invariant, for this reason, birefringent materials with three distinct refractive indices are called biaxial
19.
Pleochroism
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Pleochroism is an optical phenomenon in which a substance appears to be different colors when observed at different angles, especially with polarized light. Anisotropic crystals will have properties that vary with the direction of light. The polarization of light determines the direction of the electric field and these kinds of crystals have one or two optical axes. If absorption of light varies with the relative to the optical axis in a crystal then pleochroism results. Anisotropic crystals have double refraction of light where light of different polarizations is bent different amounts by the crystal, the components of a divided light beam follow different paths within the mineral and travel at different speeds. When the mineral is observed at some angle, light following some combination of paths and polarizations will be present, at another angle, the light passing through the crystal will be composed of another combination of light paths and polarizations, each with their own color. The light passing through the mineral will therefore have different colors when it is viewed from different angles, tetragonal, trigonal and hexagonal minerals can only show two colors and are called dichroic. Orthorhombic, monoclinic and triclinic crystals can show three and are trichroic, for example, hypersthene, with two optical axes, can have red, yellow or blue appearance when oriented in three different ways in three-dimensional space. Tourmaline is notable for exhibiting strong pleochroism, gems are sometimes cut and set either to display pleochroism or to hide it, depending on the colors and their attractiveness. The pleochroic colours are at their maximum when light is polarized parallel with a crystallographic axis, the axes are designated X, Y and Z. These axes can be determined from the appearance of a crystal in an interference pattern. Where there are two axes, the acute bisection of the axes gives Z for positive minerals and X for negative minerals. Perpendicular to these is the Y axis, the colour is measured with the polarization parallel to each direction. An absorption formula records the amount of parallel to each axis in the form of X < Y < Z with the left most having the least absorption. Minerals that are very similar often have very different pleochroic color schemes. In such cases, a section of the mineral is used and examined under polarized transmitted light with a petrographic microscope. Another device using this property to identify minerals is the dichroscope
20.
Ultraviolet
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Ultraviolet is an electromagnetic radiation with a wavelength from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays. UV radiation constitutes about 10% of the light output of the Sun. It is also produced by electric arcs and specialized lights, such as lamps, tanning lamps. Consequently, the effects of UV are greater than simple heating effects. Suntan, freckling and sunburn are familiar effects of over-exposure, along with risk of skin cancer. Living things on dry land would be damaged by ultraviolet radiation from the Sun if most of it were not filtered out by the Earths atmosphere. More-energetic, shorter-wavelength extreme UV below 121 nm ionizes air so strongly that it is absorbed before it reaches the ground, Ultraviolet is also responsible for the formation of bone-strengthening vitamin D in most land vertebrates, including humans. The UV spectrum thus has both beneficial and harmful to human health. Ultraviolet rays are invisible to most humans, the lens in a human eye ordinarily filters out UVB frequencies or higher, and humans lack color receptor adaptations for ultraviolet rays. Under some conditions, children and young adults can see ultraviolet down to wavelengths of about 310 nm, near-UV radiation is visible to some insects, mammals, and birds. Small birds have a fourth color receptor for ultraviolet rays, this gives birds true UV vision, reindeer use near-UV radiation to see polar bears, who are poorly visible in regular light because they blend in with the snow. UV also allows mammals to see urine trails, which is helpful for animals to find food in the wild. The males and females of some species look identical to the human eye. Ultraviolet means beyond violet, violet being the color of the highest frequencies of visible light, Ultraviolet has a higher frequency than violet light. He called them oxidizing rays to emphasize chemical reactivity and to them from heat rays. The terms chemical and heat rays were eventually dropped in favour of ultraviolet and infrared radiation, in 1878 the effect of short-wavelength light on sterilizing bacteria was discovered. By 1903 it was known the most effective wavelengths were around 250 nm, in 1960, the effect of ultraviolet radiation on DNA was established. The discovery of the ultraviolet radiation below 200 nm, named vacuum ultraviolet because it is absorbed by air, was made in 1893 by the German physicist Victor Schumann
21.
Fluorescence
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Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence, in most cases, the emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation. Fluorescent materials cease to glow immediately when the radiation source stops, unlike phosphorescence, Fluorescence also occurs frequently in nature in some minerals and in various biological states in many branches of the animal kingdom. An early observation of fluorescence was described in 1560 by Bernardino de Sahagún and it was derived from the wood of two tree species, Pterocarpus indicus and Eysenhardtia polystachya. The chemical compound responsible for this fluorescence is matlaline, which is the product of one of the flavonoids found in this wood. The name was derived from the fluorite, some examples of which contain traces of divalent europium. In a key experiment he used a prism to isolate ultraviolet radiation from sunlight, the specific frequencies of exciting and emitted light are dependent on the particular system. S0 is called the state of the fluorophore, and S1 is its first excited singlet state. A molecule in S1 can relax by various competing pathways and it can undergo non-radiative relaxation in which the excitation energy is dissipated as heat to the solvent. Excited organic molecules can also relax via conversion to a triplet state, relaxation from S1 can also occur through interaction with a second molecule through fluorescence quenching. Molecular oxygen is an extremely efficient quencher of fluorescence just because of its unusual triplet ground state, in most cases, the emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation, this phenomenon is known as the Stokes shift. The emitted radiation may also be of the wavelength as the absorbed radiation. Molecules that are excited through light absorption or via a different process can transfer energy to a second sensitized molecule, the fluorescence quantum yield gives the efficiency of the fluorescence process. It is defined as the ratio of the number of photons emitted to the number of photons absorbed, Φ = Number of photons emitted Number of photons absorbed The maximum fluorescence quantum yield is 1.0, each photon absorbed results in a photon emitted. Compounds with quantum yields of 0.10 are still considered quite fluorescent, thus, if the rate of any pathway changes, both the excited state lifetime and the fluorescence quantum yield will be affected. Fluorescence quantum yields are measured by comparison to a standard, the quinine salt quinine sulfate in a sulfuric acid solution is a common fluorescence standard. The fluorescence lifetime refers to the time the molecule stays in its excited state before emitting a photon. This is an instance of exponential decay, various radiative and non-radiative processes can de-populate the excited state
22.
Clay minerals
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Clay minerals are hydrous aluminium phyllosilicates, sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces. Clay minerals form in the presence of water and have been important to life and they are important constituents of soils, and have been useful to humans since ancient times in agriculture and manufacturing. Clays form flat hexagonal sheets similar to the micas, Clay minerals are common weathering products and low-temperature hydrothermal alteration products. Clay minerals are common in soils, in fine-grained sedimentary rocks such as shale, mudstone. Clay minerals are usually ultrafine-grained and so may require special techniques for their identification. These methods can be augmented by polarized light microscopy, a traditional technique establishing fundamental occurrences or petrologic relationships. Given the requirement of water, clay minerals are rare in the Solar System, though they occur extensively on Earth where water has interacted with other minerals. Clay minerals have been detected at several locations on Mars including Echus Chasma and Mawrth Vallis and the Memnonia quadrangle, spectrography has confirmed their presence on asteroids including the dwarf planet Ceres and Tempel 1 as well as Jupiters moon Europa. A1,1 clay would consist of one sheet and one octahedral sheet. A2,1 clay consists of an octahedral sheet sandwiched between two sheets, and examples are talc, vermiculite and montmorillonite. Smectite group which includes dioctahedral smectites such as montmorillonite, nontronite and beidellite, in 2013, analytical tests by the Curiosity rover found results consistent with the presence of smectite clay minerals on the planet Mars. Illite group which includes the clay-micas, illite is the only common mineral. Chlorite group includes a variety of similar minerals with considerable chemical variation. Other 2,1 clay types exist such as sepiolite or attapulgite, mixed layer clay variations exist for most of the above groups. Ordering is described as random or regular ordering, and is described by the term reichweite. Literature articles will refer to a R1 ordered illite-smectite, for example and this type would be ordered in an ISISIS fashion. R0 on the other hand describes random ordering, and other advanced ordering types are also found, mixed layer clay minerals which are perfect R1 types often get their own names. R1 ordered chlorite-smectite is known as corrensite, R1 illite-smectite is rectorite, knowledge of the nature of clay became better understood in the 1930s with advancements in x-ray diffraction technology necessary to analyze the molecular nature of clay particles
23.
Hydrate
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In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understood, in organic chemistry, a hydrate is a compound formed by the addition of water or its elements to another molecule. A molecule of water may be eliminated, for example by the action of sulfuric acid, another example is chloral hydrate, CCl3–CH2, which can be formed by reaction of water with chloral, CCl3–CH=O. Many organic molecules, as well as molecules, form crystals that incorporate water into the crystalline structure without chemical alteration of the organic molecule. The sugar trehalose, for example, exists in both a form and as a dihydrate. Protein crystals commonly have as much as 50% water content, molecules are also labeled as hydrates for historical reasons not covered above. Glucose, C6H12O6, was thought of as C66 and described as a carbohydrate. Methanol is often sold as methyl hydrate, implying the incorrect formula CH3OH2, such hydrates are also said to contain water of crystallization or water of hydration. If the water is water, where the hydrogen involved is the isotope deuterium. A colorful example is cobalt chloride, which turns blue to red upon hydration. The notation hydrated compound⋅nH2O, where n is the number of molecules per formula unit of the salt, is commonly used to show that a salt is hydrated. The n is usually a low integer, though it is possible for fractional values to occur, for example, in a monohydrate n is one, and in a hexahydrate n is 6. Numerical prefixes of Greek origin are, A hydrate which has lost water is referred to as an anhydride, a substance that does not contain any water is referred to as anhydrous. Some anhydrous compounds are hydrated so easily that they are said to be hygroscopic and are used as drying agents or desiccants, clathrate hydrates are water ice with gas molecules trapped within, they are a form of clathrate. An important example is methane hydrate, nonpolar molecules such as methane can form clathrate hydrates with water, especially under high pressure. In such cases the guest-host hydrogen bonds result in the formation of L-type Bjerrum defects in the clathrate lattice, the stability of hydrates is generally determined by the nature of the compounds, their temperature, and the relative humidity
24.
Magnesium
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Magnesium is a chemical element with symbol Mg and atomic number 12. Magnesium is the ninth most abundant element in the universe and it is produced in large, aging stars from the sequential addition of three helium nuclei to a carbon nucleus. When such stars explode as supernovas, much of the magnesium is expelled into the medium where it may recycle into new star systems. Magnesium is the eighth most abundant element in the Earths crust and the fourth most common element in the Earth, making up 13% of the planets mass and it is the third most abundant element dissolved in seawater, after sodium and chlorine. Magnesium occurs naturally only in combination with elements, where it invariably has a +2 oxidation state. The free element can be produced artificially, and is highly reactive, the free metal burns with a characteristic brilliant-white light. The metal is now obtained mainly by electrolysis of magnesium salts obtained from brine, Magnesium is less dense than aluminium, and the alloy is prized for its combination of lightness and strength. Magnesium is the eleventh most abundant element by mass in the body and is essential to all cells. Magnesium ions interact with polyphosphate compounds such as ATP, DNA, hundreds of enzymes require magnesium ions to function. Magnesium compounds are used medicinally as common laxatives, antacids, elemental magnesium is a gray-white lightweight metal, two-thirds the density of aluminium. Magnesium has the lowest melting and the lowest boiling point 1,363 K of all the alkaline earth metals, Magnesium reacts with water at room temperature, though it reacts much more slowly than calcium, a similar group 2 metal. When submerged in water, hydrogen bubbles form slowly on the surface of the metal—though, if powdered, the reaction occurs faster with higher temperatures. Magnesiums reversible reaction with water can be harnessed to store energy, Magnesium also reacts exothermically with most acids such as hydrochloric acid, producing the metal chloride and hydrogen gas, similar to the HCl reaction with aluminium, zinc, and many other metals. Magnesium is highly flammable, especially when powdered or shaved into thin strips, flame temperatures of magnesium and magnesium alloys can reach 3,100 °C, although flame height above the burning metal is usually less than 300 mm. Once ignited, such fires are difficult to extinguish, with combustion continuing in nitrogen, carbon dioxide, Magnesium may also be used as an igniter for thermite, a mixture of aluminium and iron oxide powder that ignites only at a very high temperature. When burning in air, magnesium produces a light that includes strong ultraviolet wavelengths. Magnesium powder was used for illumination in the early days of photography. Later, magnesium filament was used in electrically ignited single-use photography flashbulbs, Magnesium powder is used in fireworks and marine flares where a brilliant white light is required
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Silicate
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A silicate is a compound containing an anionic silicon compound. The great majority of the silicates are oxides, but hexafluorosilicate, orthosilicate is the anion SiO4−4 or its compounds. Related to orthosilicate are families of anions with the formula 2n−, important members are the cyclic and single chain silicates n and the sheet-forming silicates n. Silicates constitute the majority of Earths crust, as well as the terrestrial planets, rocky moons. Sand, Portland cement, and thousands of minerals are examples of silicates, silicate compounds, including the minerals, consist of silicate anions whose charge is balanced by various cations. Myriad silicate anions can exist, and each can form compounds with many different cations, hence this class of compounds is very large. Both minerals and synthetic materials fit in this class, in the vast majority of silicates, including silicate minerals, the Si occupies a tetrahedral environment, being surrounded by 4 oxygen centres. In these structures, the bonds to silicon conform to the octet rule. These tetrahedra sometimes occur as isolated SiO4−4 centres, but most commonly, commonly the silicate anions are chains, double chains, sheets, and three-dimensional frameworks. All these such species have negligible solubility in water at normal conditions, silicates are well characterized as solids, but are less commonly observed in solution. The anion SiO4−4 is the base of silicic acid, Si4. Instead, solutions of silicates are usually observed as mixtures of condensed, the nature of soluble silicates is relevant to understanding biomineralization and the synthesis of aluminosilicates, such as the industrially important catalysts called zeolites. Although the tetrahedron is the coordination geometry for silicon compounds. A well-known example of such a high number is hexafluorosilicate. Octahedral coordination by 6 oxygen centres is observed, at very high pressure, even SiO2 adopts this geometry in the mineral stishovite, a dense polymorph of silica found in the lower mantle of the Earth. This structure is formed by shock during meteorite impacts. In geology and astronomy, the silicate is used to denote types of rock that consist predominantly of silicate minerals. On Earth, a variety of silicate minerals occur in an even wider range of combinations as a result of the processes that form
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Corn starch
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Corn starch, cornstarch, cornflour or maize starch or maize is the starch derived from the corn grain or wheat. The starch is obtained from the endosperm of the kernel, corn starch is a popular food ingredient used in thickening sauces or soups, and is used in making corn syrup and other sugars. When mixed with a fluid, cornstarch can rearrange itself into a non-Newtonian fluid, for example, adding water transforms cornstarch into a material commonly known as Oobleck while adding oil transforms cornstarch into a Electrorheological fluid. The concept can be explained through the mixture termed cornflour slime, cornstarch was discovered in 1840 by Thomas Kingsford, superintendent of a wheat starch factory in Jersey City, New Jersey. Until 1851, corn starch was used primarily for starching laundry, cornstarch is used as a thickening agent in liquid-based foods, usually by mixing it with a lower-temperature liquid to form a paste or slurry. It is sometimes preferred over flour alone because it forms a translucent mixture, as the starch is heated, the molecular chains unravel, allowing them to collide with other starch chains to form a mesh, thickening the liquid. It is usually included as an agent in powdered sugar. A common substitute is arrowroot, which replaces cornstarch on a 1,1 ratio, chicken nuggets with a thin outer layer of cornstarch allows increased oil absorption and crispness after the latter stages of frying. Baby powder often includes cornstarch among its ingredients, cornstarch can be used to manufacture bioplastics. Food producers reduce production costs by adding varying amounts of cornstarch to foods, for example to cheese and this is more common in the United States of America where the Congress and the Department of Agriculture subsidize and reduce its cost to food manufacturers. When roasted in a standard oven it produced dextrin, a compound with uses ranging from adhesive to binder for fireworks. Cornstarch is the preferred anti-stick agent on medical products made from latex, including condoms, diaphragms. Prior usage of talc was abandoned as talc was believed to be a carcinogen, cornstarch has properties that allows it to slowly releases a type of glucose over time. Thus, cornstarch has been used to supply glucose and maintain blood sugar levels to humans who have glycogen storage disease, cornstarch can be used starting at age 6 –12 months which allows feeds to be spaced and glucose fluctuations to be minimized. The corn is steeped for 30 to 48 hours, which ferments it slightly, the germ is separated from the endosperm and those two components are ground separately. Next the starch is removed from each by washing, the starch is separated from the corn steep liquor, the cereal germ, the fibers and the corn gluten mostly in hydrocyclones and centrifuges, and then dried. This process is called wet milling, finally, the starch may be modified for specific purposes. Called cornstarch in the United States and Canada, called cornflour in the United Kingdom, Ireland, Israel and some Commonwealth countries
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Baby powder
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Baby powder is an astringent powder used for preventing diaper rash, as a deodorant, and for other cosmetic uses. It may be composed of talc or corn starch, talcum powder is dangerous if inhaled since it may cause aspiration pneumonia or granuloma. Pediatricians generally prefer cornstarch to talc because it is unlikely to be easily inhaled, baby powder can also be used as a shampoo, cleaning agent, and freshener. Some studies have found a relationship between perineal talc use by adult women and incidence of ovarian cancer. However, there is not a consensus about a causal link
28.
Foliation (geology)
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Foliation in geology refers to repetitive layering in metamorphic rocks. Each layer may be as thin as a sheet of paper, the word comes from the Latin folium, meaning leaf, and refers to the sheet-like planar structure. It is caused by shearing forces, or differential pressure, the layers form parallel to the direction of the shear, or perpendicular to the direction of higher pressure. Nonfoliated metamorphic rocks are formed in the absence of significant differential pressure or sheer. Foliation is common in rocks affected by the regional metamorphic compression typical of areas of mountain belt formation, more technically, foliation is any penetrative planar fabric present in metamorphic rocks. Rocks exhibiting foliation include the sequence formed by the prograde metamorphism of mudrocks, slate, phyllite, schist. The slatey cleavage typical of slate is due to the orientation of microscopic phyllosilicate crystals. In gneiss the foliation is more typically represented by compositional banding due to segregation of mineral phases, foliated rock is also known as S-tectonite in sheared rock masses. Foliation is usually formed by the orientation of minerals within a rock. Usually this is a result of physical force, and its effect upon the growth of minerals. The planar fabric of a foliation typically forms at right angles to the principal strain direction. In sheared zones, however, planar fabric within a rock may not be perpendicular to the principal stress direction due to rotation, mass transport. Foliation may be formed by realignment of micas and clays via physical rotation of the minerals within the rock, often this foliation is associated with diagenetic metamorphism and low-grade burial metamorphism. Foliation may parallel original sedimentary bedding, but more often is oriented at angle to it. The growth of platy minerals, typically of the group, is usually a result of prograde metamorphic reactions during deformation. Often, retrograde metamorphism will not form a foliation because unroofing of a belt is not accompanied by significant compressive stress. Thermal metamorphism in the aureole of a granite is also unlikely to result in growth of mica in a foliation, alignment of tabular minerals in metamorphic rocks, igneous rocks and intrusive rocks may form a foliation. Typical examples of metamorphic rocks include porphyroblastic schists where large, oblate minerals form an alignment either due to growth or rotation in the groundmass, igneous rocks can become foliated by alignment of cumulate crystals during convection in large magma chambers, especially ultramafic intrusions, and typically plagioclase laths
29.
Fiber
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Fiber or fibre is a natural or synthetic substance that is significantly longer than it is wide. Fibers are often used in the manufacture of other materials, the strongest engineering materials often incorporate fibers, for example carbon fiber and ultra-high-molecular-weight polyethylene. Natural fibers develop or occur in the shape, and include those produced by plants, animals. Plant fibers are employed in the manufacture of paper and textile, wood fiber, distinguished from vegetable fiber, is from tree sources. Forms include groundwood, lacebark, thermomechanical pulp, and bleached or unbleached kraft or sulfite pulps, animal fibers consist largely of particular proteins. Instances are silkworm silk, spider silk, sinew, catgut, wool, sea silk and hair such as wool, mohair and angora, fur such as sheepskin, rabbit, mink, fox, beaver. Mineral fibers include the asbestos group, asbestos is the only naturally occurring long mineral fiber. Six minerals have been classified as asbestos including chrysotile of the serpentine class, short, fiber-like minerals include wollastonite and palygorskite. Instances are collagen family of proteins, tendon, muscle proteins like actin, cell proteins like microtubules and many others, spider silk, sinew, man-made or chemical fibers are fibers whose chemical composition, structure, and properties are significantly modified during the manufacturing process. Man-made fibers consist of regenerated fibers and synthetic fibers, the earliest semi-synthetic fiber is the cellulose regenerated fiber, rayon. Most semi-synthetic fibers are cellulose regenerated fibers, cellulose fibers are a subset of man-made fibers, regenerated from natural cellulose. The cellulose comes from sources, rayon from tree wood fiber, Modal from beech trees, bamboo fiber from bamboo, seacell from seaweed. In the production of fibers, the cellulose is reduced to a fairly pure form as a viscous mass. Therefore, the process leaves few characteristics distinctive of the natural source material in the finished products. Some examples are, rayon bamboo fiber Lyocell, a brand of rayon Modal, historically, cellulose diacetate and -triacetate were classified under the term rayon, but are now considered distinct materials. Synthetic come entirely from materials such as petrochemicals, unlike those man-made fibers derived from such natural substances as cellulose or protein. Metallic fibers can be drawn from ductile metals such as copper, gold or silver and extruded or deposited from more brittle ones, such as nickel, carbon fibers are often based on oxydized and via pyrolysis carbonized polymers like PAN, but the end product is almost pure carbon. Silicon carbide fibers, where the polymers are not hydrocarbons but polymers
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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
31.
Elasticity (physics)
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In physics, elasticity is the ability of a body to resist a distorting influence or deforming force and to return to its original size and shape when that influence or force is removed. Solid objects will deform when adequate forces are applied on them, if the material is elastic, the object will return to its initial shape and size when these forces are removed. The physical reasons for elastic behavior can be different for different materials. In metals, the atomic lattice changes size and shape when forces are applied, when forces are removed, the lattice goes back to the original lower energy state. For rubbers and other polymers, elasticity is caused by the stretching of polymer chains when forces are applied, perfect elasticity is an approximation of the real world. The most elastic body in modern science found is Quartz fibre which is not even a perfect elastic body, so perfect elastic body is an ideal concept only. Most materials which possess elasticity in practice remain purely elastic only up to very small deformations. In engineering, the amount of elasticity of a material is determined by two types of material parameter, the first type of material parameter is called a modulus, which measures the amount of force per unit area needed to achieve a given amount of deformation. The SI unit of modulus is the pascal, a higher modulus typically indicates that the material is harder to deform. The second type of measures the elastic limit, the maximum stress that can arise in a material before the onset of permanent deformation. Its SI unit is also pascal, when describing the relative elasticities of two materials, both the modulus and the elastic limit have to be considered. Rubbers typically have a low modulus and tend to stretch a lot, of two rubber materials with the same elastic limit, the one with a lower modulus will appear to be more elastic, which is however not correct. When an elastic material is deformed due to a force, it experiences internal resistance to the deformation. The various moduli apply to different kinds of deformation, for instance, Youngs modulus applies to extension/compression of a body, whereas the shear modulus applies to its shear. The elasticity of materials is described by a curve, which shows the relation between stress and strain. The curve is nonlinear, but it can be approximated as linear for sufficiently small deformations. For even higher stresses, materials exhibit behavior, that is, they deform irreversibly. Elasticity is not exhibited only by solids, non-Newtonian fluids, such as viscoelastic fluids, in response to a small, rapidly applied and removed strain, these fluids may deform and then return to their original shape. Under larger strains, or strains applied for longer periods of time, because the elasticity of a material is described in terms of a stress-strain relation, it is essential that the terms stress and strain be defined without ambiguity
32.
Nail (anatomy)
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A nail is a horn-like envelope covering the tips of the fingers and toes in humans, most non-human primates, and a few other mammals. Nails are similar to claws in other animals, fingernails and toenails are made of a tough protective protein called keratin. This protein is found in the hooves and horns of different animals. The nail consists of the plate, the nail matrix and the nail bed below it. The matrix, sometimes called the matrix unguis, keratogenous membrane, nail matrix and it is the part of the nail bed that is beneath the nail and contains nerves, lymph and blood vessels. The matrix is responsible for producing cells that become the nail plate. The width and thickness of the plate is determined by the size, length. The matrix will continue to grow as long as it receives nutrition, as new nail plate cells are made, they push older nail plate cells forward, and in this way older cells become compressed, flat, and translucent. This makes the capillaries in the nail bed below visible, resulting in a pink color, the lunula is the visible part of the matrix, the whitish crescent-shaped base of the visible nail. The lunula can best be seen in the thumb and may not be visible in the little finger, the nail bed is the skin beneath the nail plate. The epidermis is attached to the dermis by tiny longitudinal grooves called matrix crests, in old age, the nail plate becomes thinner, and these grooves become more visible. The nail sinus is where the root is, i. e. the base of the nail underneath the skin. It originates from the actively growing tissue below, the matrix, the nail plate is the hard part of the nail, made of translucent keratin protein. Several layers of dead, compacted cells cause the nail to be strong and its shape is determined by the form of the underlying bone. In common usage, the word often refers to this part only. The free margin or distal edge is the margin of the nail plate corresponding to the abrasive or cutting edge of the nail. The hyponychium is the epithelium located beneath the nail plate at the junction between the edge and the skin of the fingertip. It forms a seal that protects the nail bed, the onychodermal band is the seal between the nail plate and the hyponychium
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Soapstone
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Soapstone is a talc-schist, which is a type of metamorphic rock. It is largely composed of the mineral talc and is rich in magnesium. It has been a medium for carving for thousands of years, petrologically, soapstone is composed dominantly of talc, with varying amounts of chlorite and amphiboles, and trace to minor iron-chromium oxides. It may be schistose or massive, Soapstone is formed by the metamorphism of ultramafic protoliths and the metasomatism of siliceous dolostones. By mass, pure steatite is approximately 63. 37% silica,31. 88% magnesia and 4. 74% water and it commonly contains minor quantities of other oxides such as CaO or Al2O3. However, this mineral typically does not have such a feel as soapstone. Soapstone is relatively soft because of its high content, talc having a definitional value of 1 on the Mohs hardness scale. Softer grades may feel similar to soap when touched, hence the name, common, non-architectural grades of soapstone can just barely be scratched with a fingernail and are thus considered to have a hardness of 2.5 on the Mohs scale. If a candidate rock cannot be scratched with a knife blade, Soapstone is often used as an insulator for housing and electrical components, due to its durability and electrical characteristics and because it can be pressed into complex shapes before firing. Soapstone undergoes transformations when heated to temperatures of 1000–1200 °C into enstatite and cristobalite, in the Mohs scale, Soapstone is used for inlaid designs, sculpture, coasters, and kitchen countertops and sinks. The Inuit often use soapstone for traditional carvings, some Native American tribes and bands make bowls, cooking slabs, and other objects from soapstone, historically, this was particularly common during the Late Archaic archaeological period. Locally quarried soapstone was used for gravemarkers in 19th century northeast Georgia, US, around Dahlonega, vikings hewed soapstone directly from the stone face, shaped it into cooking-pots, and sold these at home and abroad. It is also used for counter tops and bathroom tiling because of the ease of working the material, a weathered or aged appearance will occur naturally over time as the patina is enhanced. Applying mineral oil simply darkens the appearance of the stone, it does not protect it in any way, tepe Yahya, an ancient trading city in southeastern Iran, was a center for the production and distribution of soapstone in the 5th–3rd millennia BC. It was also used in Minoan Crete, at the Palace of Knossos, archaeological recovery has included a magnificent libation table made of steatite. The Yoruba of West Nigeria utilized soapstone for several statues most notably at Esie where archaeologists have uncovered hundreds of male and female statues, about half of life size. The Yoruba of Ife also produced a miniature soapstone obelisk with metal studs called superstitiously the staff of Oranmiyan Soapstone has been used in India for centuries as a medium for carving, mining to meet world-wide demand for soapstone is threatening the habitat of Indias tigers. These handicrafts are sold in street markets found in cities across the state
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Metamorphic rock
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Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism, which means change in form. The original rock is subjected to heat and pressure, causing profound physical and/or chemical change, the protolith may be a sedimentary, an igneous, or even an existing type of metamorphic rock. Metamorphic rocks make up a part of the Earths crust. They are classified by texture and by chemical and mineral assemblage and they may be formed simply by being deep beneath the Earths surface, subjected to high temperatures and the great pressure of the rock layers above it. They can form from tectonic processes such as continental collisions, which cause horizontal pressure and they are also formed when rock is heated up by the intrusion of hot molten rock called magma from the Earths interior. The study of rocks provides information about the temperatures and pressures that occur at great depths within the Earths crust. Some examples of rocks are gneiss, slate, marble, schist. Metamorphic minerals are those that only at the high temperatures and pressures associated with the process of metamorphism. These minerals, known as index minerals, include sillimanite, kyanite, staurolite, andalusite, and some garnet. Other minerals, such as olivines, pyroxenes, amphiboles, micas, feldspars, and quartz, may be found in metamorphic rocks and these minerals formed during the crystallization of igneous rocks. They are stable at temperatures and pressures and may remain chemically unchanged during the metamorphic process. However, all minerals are only within certain limits. The change in the size of the rock during the process of metamorphism is called recrystallization. Both high temperatures and pressures contribute to recrystallization, high temperatures allow the atoms and ions in solid crystals to migrate, thus reorganizing the crystals, while high pressures cause solution of the crystals within the rock at their point of contact. The layering within metamorphic rocks is called foliation, and it occurs when a rock is being shortened along one axis during recrystallization. This causes the platy or elongated crystals of minerals, such as mica and chlorite and this results in a banded, or foliated rock, with the bands showing the colors of the minerals that formed them. Textures are separated into foliated and non-foliated categories, foliated rock is a product of differential stress that deforms the rock in one plane, sometimes creating a plane of cleavage. For example, slate is a metamorphic rock, originating from shale
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Arabic
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Arabic is a Central Semitic language that was first spoken in Iron Age northwestern Arabia and is now the lingua franca of the Arab world. Arabic is also the language of 1.7 billion Muslims. It is one of six languages of the United Nations. The modern written language is derived from the language of the Quran and it is widely taught in schools and universities, and is used to varying degrees in workplaces, government, and the media. The two formal varieties are grouped together as Literary Arabic, which is the language of 26 states. Modern Standard Arabic largely follows the standards of Quranic Arabic. Much of the new vocabulary is used to denote concepts that have arisen in the post-Quranic era, Arabic has influenced many languages around the globe throughout its history. During the Middle Ages, Literary Arabic was a vehicle of culture in Europe, especially in science, mathematics. As a result, many European languages have borrowed many words from it. Many words of Arabic origin are found in ancient languages like Latin. Balkan languages, including Greek, have acquired a significant number of Arabic words through contact with Ottoman Turkish. Arabic has also borrowed words from languages including Greek and Persian in medieval times. Arabic is a Central Semitic language, closely related to the Northwest Semitic languages, the Ancient South Arabian languages, the Semitic languages changed a great deal between Proto-Semitic and the establishment of the Central Semitic languages, particularly in grammar. Innovations of the Central Semitic languages—all maintained in Arabic—include, The conversion of the suffix-conjugated stative formation into a past tense, the conversion of the prefix-conjugated preterite-tense formation into a present tense. The elimination of other prefix-conjugated mood/aspect forms in favor of new moods formed by endings attached to the prefix-conjugation forms, the development of an internal passive. These features are evidence of descent from a hypothetical ancestor. In the southwest, various Central Semitic languages both belonging to and outside of the Ancient South Arabian family were spoken and it is also believed that the ancestors of the Modern South Arabian languages were also spoken in southern Arabia at this time. To the north, in the oases of northern Hijaz, Dadanitic and Taymanitic held some prestige as inscriptional languages, in Najd and parts of western Arabia, a language known to scholars as Thamudic C is attested
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Persian language
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Persian, also known by its endonym Farsi, is one of the Western Iranian languages within the Indo-Iranian branch of the Indo-European language family. It is primarily spoken in Iran, Afghanistan, and Tajikistan and it is mostly written in the Persian alphabet, a modified variant of the Arabic script. Its grammar is similar to that of many contemporary European languages, Persian gets its name from its origin at the capital of the Achaemenid Empire, Persis, hence the name Persian. A Persian-speaking person may be referred to as Persophone, there are approximately 110 million Persian speakers worldwide, with the language holding official status in Iran, Afghanistan, and Tajikistan. For centuries, Persian has also been a cultural language in other regions of Western Asia, Central Asia. It also exerted influence on Arabic, particularly Bahrani Arabic. Persian is one of the Western Iranian languages within the Indo-European family, other Western Iranian languages are the Kurdish languages, Gilaki, Mazanderani, Talysh, and Balochi. Persian is classified as a member of the Southwestern subgroup within Western Iranian along with Lari, Kumzari, in Persian, the language is known by several names, Western Persian, Parsi or Farsi has been the name used by all native speakers until the 20th century. Since the latter decades of the 20th century, for reasons, in English. Tajiki is the variety of Persian spoken in Tajikistan and Uzbekistan by the Tajiks, according to the Oxford English Dictionary, the term Persian as a language name is first attested in English in the mid-16th century. Native Iranian Persian speakers call it Fārsi, Farsi is the Arabicized form of Pārsi, subsequent to Muslim conquest of Persia, due to a lack of the phoneme /p/ in Standard Arabic. The origin of the name Farsi and the place of origin of the language which is Fars Province is the Arabicized form of Pārs, in English, this language has historically been known as Persian, though Farsi has also gained some currency. Farsi is encountered in some literature as a name for the language. In modern English the word Farsi refers to the language while Parsi describes Zoroastrians, some Persian language scholars such as Ehsan Yarshater, editor of Encyclopædia Iranica, and University of Arizona professor Kamran Talattof, have also rejected the usage of Farsi in their articles. The international language-encoding standard ISO 639-1 uses the code fa, as its system is mostly based on the local names. The more detailed standard ISO 639-3 uses the name Persian for the dialect continuum spoken across Iran and Afghanistan and this consists of the individual languages Dari and Iranian Persian. Currently, Voice of America, BBC World Service, Deutsche Welle, Radio Free Europe/Radio Liberty also includes a Tajik service and an Afghan service. This is also the case for the American Association of Teachers of Persian, The Centre for Promotion of Persian Language and Literature, Persian is an Iranian language belonging to the Indo-Iranian branch of the Indo-European family of languages
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Mica
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The mica group of sheet silicate minerals includes several closely related materials having nearly perfect basal cleavage. All are monoclinic, with a tendency towards pseudohexagonal crystals, and are similar in chemical composition, the nearly perfect cleavage, which is the most prominent characteristic of mica, is explained by the hexagonal sheet-like arrangement of its atoms. The word mica is derived from the Latin word mica, meaning a crumb, and probably influenced by micare, to glitter. Chemically, micas can be given the general formula X2Y4–6Z8O204 in which X is K, Na, or Ca or less commonly Ba, Rb, or Cs, Y is Al, Mg, or Fe or less commonly Mn, Cr, Ti, Li, etc. Z is chiefly Si or Al, but also may include Fe3+ or Ti, structurally, micas can be classed as dioctahedral and trioctahedral. If the X ion is K or Na, the mica is a common mica, whereas if the X ion is Ca, mica is widely distributed and occurs in igneous, metamorphic and sedimentary regimes. Large crystals of mica used for various applications are typically mined from granitic pegmatites, until the 19th century, large crystals of mica were quite rare and expensive as a result of the limited supply in Europe. However, their price dramatically dropped when large reserves were found and mined in Africa, the largest documented single crystal of mica was found in Lacey Mine, Ontario, Canada, it measured 10 ×4.3 ×4.3 m and weighed about 330 tonnes. Similar-sized crystals were found in Karelia, Russia. The British Geological Survey reported that as of 2005, Koderma district in Jharkhand state in India had the largest deposits of mica in the world. China was the top producer of mica with almost a third of the share, closely followed by the US, South Korea. Large deposits of mica were mined in New England from the 19th century to the 1970s. Large mines existed in Connecticut, New Hampshire, and Maine, scrap and flake mica is produced all over the world. In 2010, the producers were Russia, Finland, United States, South Korea, France. The total production was 350,000 t, although no data were available for China. Most sheet mica was produced in India and Russia, flake mica comes from several sources, the metamorphic rock called schist as a byproduct of processing feldspar and kaolin resources, from placer deposits, and from pegmatites. Sheet mica is considerably less abundant than flake and scrap mica, the most important sources of sheet mica are pegmatite deposits. Sheet mica prices vary with grade and can range from less than $1 per kilogram for low-quality mica to more than $2,000 per kilogram for the highest quality, the mica group represents 37 phyllosilicate minerals that have a layered or platy texture
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Selenite (mineral)
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Selenite, satin spar, desert rose, and gypsum flower are four varieties of the mineral gypsum, all four varieties show obvious crystalline structure. The four crystalline varieties of gypsum are sometimes grouped together and called selenite, all varieties of gypsum, including selenite and alabaster, are composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. Selenite contains no significant selenium, the similarity of names comes from both substances being named from the Ancient Greek word for the Moon. The etymology of selenite is through Middle English selinete, from Latin selenites, from Greek selēnitēs, literally, moonstone or stone of the moon, the ancients had a belief that certain transparent crystals waxed and waned with the moon. From the 15th century, selenite has referred specifically to the variety of gypsum that occurs in transparent crystals or crystalline masses, all varieties of gypsum are very soft minerals. This is the most important identifying characteristic of gypsum, as any variety of gypsum can be scratched with a fingernail. Also, because gypsum has natural thermal insulating properties, all varieties feel warm to the touch, though sometimes grouped together as selenite, the four crystalline varieties have differences. General identifying descriptions of the related crystalline varieties are, most often transparent and colorless, crystal habit refers to the shapes that crystals exhibit. Selenite crystals commonly occur as tabular, reticular, and columnar crystals, often with no imperfections or inclusions, many collectible selenite crystals have interesting inclusions such as, accompanying related minerals, interior druse, dendrites, and fossils. In some rare instances, water was encased as a fluid inclusion when the crystal formed, selenite crystals sometimes form in thin tabular or mica-like sheets and have been used as glass panes as at Santa Sabina in Rome. Selenite crystals sometimes will also exhibit bladed rosette habit often with accompanying transparent, selenite crystals can be found both attached to a matrix or base rock, but can commonly be found as entire free-floating crystals, often in clay beds. Satin spar is almost always prismatic and fibrous in a crystal habit. Satin spar often occurs in seams, some of them quite long, desert roses are most often bladed, exhibiting the familiar shape of a rose, and almost always have an exterior druse. Desert roses are almost always unattached to a matrix or base rock, gypsum flowers are most often acicular, scaly, stellate, and lenticular. Selenite crystals can also exhibit “arrow/spear-head” as well as “duck-bill” twins, both selenite crystals and gypsum flowers sometimes form quite densely in acicular mats or nets, and can be quite brittle and fragile. Gypsum flowers are attached to a matrix or base rock. Gypsum crystals are colorless, white, gray, brown, beige, orange, pink, yellow, light red, and green. Colors are caused by the presence of mineral inclusions such as, copper ores, sulfur and sulfides, silver, iron ores, coal, calcite, dolomite
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Serpentine subgroup
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The serpentine subgroup are greenish, brownish, or spotted minerals commonly found in serpentinite rocks. They are used as a source of magnesium and asbestos, the name is thought to come from the greenish color being that of a serpent. In mineralogy and gemology, serpentine may refer to any of 20 varieties belonging to the serpentine group, owing to admixture, these varieties are not always easy to individualize, and distinctions are not usually made. There are three important mineral polymorphs of serpentine, antigorite, chrysotile and lizardite, the serpentine group of minerals are polymorphous, meaning that they have the same chemical formulae, but the atoms are arranged into different structures, or crystal lattices. Chrysotile, which has a habit, is one polymorph of serpentine and is an important component of asbestos. Other polymorphs in the group may have a platy habit. Antigorite and lizardite are the polymorphs with platy habit, many types of serpentine have been used for jewellery and hardstone carving, sometimes under the name false jade or Teton jade. Their olive green colour and smooth or scaly appearance is the basis of the name from the Latin serpentinus, meaning serpent rock and they have their origins in metamorphic alterations of peridotite and pyroxene. Serpentines may also pseudomorphously replace other magnesium silicates, alterations may be incomplete, causing physical properties of serpentines to vary widely. Where they form a significant part of the surface, the soil is unusually high in clay. Antigorite is the polymorph of serpentine that most commonly forms during metamorphism of wet ultramafic rocks and is stable at the highest temperatures—to over 600 °C at depths of 60 km or so. In contrast, lizardite and chrysotile typically form near the Earths surface and break down at low temperatures. It has been suggested that chrysotile is never stable relative to either of the other two serpentine polymorphs, samples of the oceanic crust and uppermost mantle from ocean basins document that ultramafic rocks there commonly contain abundant serpentine. Antigorite contains water in its structure, about 13 percent by weight, the flora is generally very distinctive, with specialised, slow-growing species. Areas of serpentine-derived soil will show as strips of shrubland and open, scattered small trees within otherwise forested areas, most serpentines are opaque to translucent, light, soft, infusible and susceptible to acids. All are microcrystalline and massive in habit, never being found as single crystals, lustre may be vitreous, greasy or silky. Colours range from white to grey, yellow to green, and brown to black, many are intergrown with other minerals, such as calcite and dolomite. Occurrence is worldwide, New Caledonia, Canada, US, Afghanistan, Britain, Greece, China, Ural Mountains, France, Korea, Austria, India, Myanmar, New Zealand, Norway and Italy are notable localities
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Pyroxene
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The pyroxenes are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes are silicon-aluminum oxides with Ca, Na, Fe, Mg, Zn, Mn, Li substituting for Si, although aluminium substitutes extensively for silicon in silicates such as feldspars and amphiboles, the substitution occurs only to a limited extent in most pyroxenes. They share a structure consisting of single chains of silica tetrahedra. The name pyroxene is derived from the Ancient Greek words for fire, however, they are simply early-forming minerals that crystallized before the lava erupted. The upper mantle of Earth is composed mainly of olivine and pyroxene, a piece of the mantle is shown at right and is dominated by olivine, typical for common peridotite. Pyroxene and feldspar are the minerals in basalt and gabbro. Pyroxene minerals are named according to the chemical species occupying the X site, the Y site, cations in Y site are closely bound to 6 oxygens in octahedral coordination. Cations in the X site can be coordinated with 6 to 8 oxygen atoms, twenty mineral names are recognised by the International Mineralogical Associations Commission on New Minerals and Mineral Names and 105 previously used names have been discarded. A typical pyroxene has mostly silicon in the site and predominately ions with a charge of +2 in both the X and Y sites, giving the approximate formula XYT2O6. The names of the common calcium – iron – magnesium pyroxenes are defined in the pyroxene quadrilateral shown in Figure 2, the enstatite-ferrosilite series contain up to 5 mol. % calcium and exists in three polymorphs, orthorhombic orthoenstatite and protoenstatite and monoclinic clinoenstatite. Increasing the calcium content prevents the formation of the orthorhombic phases, there is not complete solid solution in calcium content and Mg-Fe-Ca pyroxenes with calcium contents between about 15 and 25 mol. % are not stable with respect to a pair of exolved crystals. This leads to a miscibility gap between pigeonite and augite compositions, there is an arbitrary separation between augite and the diopside-hedenbergite solid solution. The divide is taken at >45 mol. % Ca, as the calcium ion cannot occupy the Y site, pyroxenes with more than 50 mol. % calcium are not possible. A related mineral wollastonite has the formula of the hypothetical calcium end member, magnesium, calcium and iron are by no means the only cations that can occupy the X and Y sites in the pyroxene structure. A second important series of minerals are the sodium-rich pyroxenes. The inclusion of sodium, which has a charge of +1, in jadeite and aegirine this is added by the inclusion of a +3 cation on the Y site. Table 1 shows the range of other cations that can be accommodated in the pyroxene structure. For example, Na and Al give the jadeite composition, coupled substitution of a 1+ ion on the X site and a mixture of equal numbers of 2+ and 4+ ions on the Y site
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Amphibole
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Amphiboles can be green, black, colorless, white, yellow, blue, or brown. The International Mineralogical Association currently classifies amphiboles as a mineral supergroup, amphiboles crystallize into two crystal systems, monoclinic and orthorhombic. In chemical composition and general characteristics they are similar to the pyroxenes, the chief differences from pyroxenes are that amphiboles contain essential hydroxyl or halogen and the basic structure is a double chain of tetrahedra. Most apparent, in specimens, is that amphiboles form oblique cleavage planes. Amphiboles are also less dense than the corresponding pyroxenes. In optical characteristics, many amphiboles are distinguished by their stronger pleochroism, amphiboles are the primary constituent of amphibolites. Amphiboles are minerals of either igneous or metamorphic origin, in the former case occurring as constituents of rocks, such as granite, diorite, andesite. Calcium is sometimes a constituent of naturally occurring amphiboles and those of metamorphic origin include examples such as those developed in limestones by contact metamorphism and those formed by the alteration of other ferromagnesian minerals. Pseudomorphs of amphibole after pyroxene are known as uralite, the name amphibole was used by René Just Haüy to include tremolite, actinolite, tourmaline and hornblende. The group was so named by Haüy in allusion to the variety, in composition and appearance. This term has since applied to the whole group. Numerous sub-species and varieties are distinguished, the important of which are tabulated below in two series. The formulae of each will be seen to be built on the general double-chain silicate formula RSi4O11, four of the amphibole minerals are among the minerals commonly called asbestos. These are, anthophyllite, riebeckite, cummingtonite/grunerite series, and actinolite/tremolite series, the cummingtonite/grunerite series is often termed amosite or brown asbestos, riebeckite is known as crocidolite or blue asbestos. These are generally called amphibole asbestos, anthophyllite occurs as brownish, fibrous or lamellar masses with hornblende in mica-schist at Kongsberg in Norway and some other localities. An aluminous related species is known as gedrite and a deep green Russian variety containing little iron as kupfferite, hornblende is an important constituent of many igneous rocks. It is also an important constituent of amphibolites formed by metamorphism of basalt, actinolite is an important and common member of the monoclinic series, forming radiating groups of acicular crystals of a bright green or greyish-green color. It occurs frequently as a constituent of greenschists, the name is a translation of the old German word Strahlstein
