1.
Nesosilicate
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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
2.
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
3.
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
4.
Cubic crystal system
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In crystallography, the cubic crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals, there are three main varieties of these crystals, Primitive cubic Body-centered cubic, Face-centered cubic Each is subdivided into other variants listed below. Note that although the cell in these crystals is conventionally taken to be a cube. This is related to the fact that in most cubic crystal systems, a classic isometric crystal has square or pentagonal faces. The three Bravais lattices in the crystal system are, The primitive cubic system consists of one lattice point on each corner of the cube. Each atom at a point is then shared equally between eight adjacent cubes, and the unit cell therefore contains in total one atom. The body-centered cubic system has one point in the center of the unit cell in addition to the eight corner points. It has a net total of 2 lattice points per unit cell, Each sphere in a cF lattice has coordination number 12. The face-centered cubic system is related to the hexagonal close packed system. The plane of a cubic system is a hexagonal grid. Attempting to create a C-centered cubic crystal system would result in a simple tetragonal Bravais lattice, there are a total 36 cubic space groups. Other terms for hexoctahedral are, normal class, holohedral, ditesseral central class, a simple cubic unit cell has a single cubic void in the center. Additionally, there are 24 tetrahedral voids located in a square spacing around each octahedral void and these tetrahedral voids are not local maxima and are not technically voids, but they do occasionally appear in multi-atom unit cells. A face-centered cubic unit cell has eight tetrahedral voids located midway between each corner and the center of the cell, for a total of eight net tetrahedral voids. One important characteristic of a structure is its atomic packing factor. This is calculated by assuming all the atoms are identical spheres. The atomic packing factor is the proportion of space filled by these spheres, assuming one atom per lattice point, in a primitive cubic lattice with cube side length a, the sphere radius would be a⁄2 and the atomic packing factor turns out to be about 0.524. Similarly, in a bcc lattice, the atomic packing factor is 0.680, as a rule, since atoms in a solid attract each other, the more tightly packed arrangements of atoms tend to be more common
5.
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
6.
H-M symbol
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In geometry, Hermann–Mauguin notation is used to represent the symmetry elements in point groups, plane groups and space groups. It is named after the German crystallographer Carl Hermann and the French mineralogist Charles-Victor Mauguin and this notation is sometimes called international notation, because it was adopted as standard by the International Tables For Crystallography since their first edition in 1935. Rotation axes are denoted by a number n —1,2,3,4,5,6,7,8, for improper rotations, Hermann–Mauguin symbols show rotoinversion axes, unlike Schoenflies and Shubnikov notations, where the preference is given to rotation-reflection axes. The rotoinversion axes are represented by the number with a macron. The symbol for a plane is m. The direction of the plane is defined as the direction of perpendicular to the face. Hermann–Mauguin symbols show symmetrically non-equivalent axes and planes, the direction of a symmetry element is represented by its position in the Hermann–Mauguin symbol. If a rotation axis n and a mirror plane m have the same direction, if two or more axes have the same direction, the axis with higher symmetry is shown. Higher symmetry means that the axis generates a pattern with more points, for example, rotation axes 3,4,5,6,7,8 generate 3-, 4-, 5-, 6-, 7-, 8-point patterns, respectively. Improper rotation axes 3,4,5,6,7,8 generate 6-, 4-, 10-, 6-, 14-, 8-point patterns, if both, the rotation and rotoinversion axes satisfy the previous rule, the rotation axis should be chosen. For example, 3/m combination is equivalent to 6, since 6 generates 6 points, and 3 generates only 3,6 should be written instead of 3/m. Analogously, in the case when both 3 and 3 axes are present,3 should be written, however we write 4/m, not 4/m, because both 4 and 4 generate four points. Finally, the Hermann–Mauguin symbol depends on the type of the group and these groups may contain only two-fold axes, mirror planes, and inversion center. These are the point groups 1 and 1,2, m, and 2/m, and 222, 2/m2/m2/m. If the symbol contains three positions, then they denote symmetry elements in the x, y, z direction, First position — primary direction — z direction, assigned to the higher-order axis. Second position — symmetrically equivalent secondary directions, which are perpendicular to the z-axis and these can be 2, m, or 2/m. Third position — symmetrically equivalent tertiary directions, passing between secondary directions and these can be 2, m, or 2/m. These are the crystallographic groups 3,32, 3m,3, and 32/m,4,422, 4mm,4, 42m, 4/m, and 4/m2/m2/m, and 6,622, 6mm,6, 6m2, 6/m, and 6/m2/m2/m
7.
Space group
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In mathematics, physics and chemistry, a space group is the symmetry group of a configuration in space, usually in three dimensions. In three dimensions, there are 219 distinct types, or 230 if chiral copies are considered distinct, Space groups are also studied in dimensions other than 3 where they are sometimes called Bieberbach groups, and are discrete cocompact groups of isometries of an oriented Euclidean space. In crystallography, space groups are called the crystallographic or Fedorov groups. A definitive source regarding 3-dimensional space groups is the International Tables for Crystallography, in 1879 Leonhard Sohncke listed the 65 space groups whose elements preserve the orientation. More accurately, he listed 66 groups, but Fedorov and Schönflies both noticed that two of them were really the same, the space groups in 3 dimensions were first enumerated by Fedorov, and shortly afterwards were independently enumerated by Schönflies. The correct list of 230 space groups was found by 1892 during correspondence between Fedorov and Schönflies, burckhardt describes the history of the discovery of the space groups in detail. The space groups in three dimensions are made from combinations of the 32 crystallographic point groups with the 14 Bravais lattices, the combination of all these symmetry operations results in a total of 230 different space groups describing all possible crystal symmetries. The elements of the space group fixing a point of space are rotations, reflections, the identity element, the translations form a normal abelian subgroup of rank 3, called the Bravais lattice. There are 14 possible types of Bravais lattice, the quotient of the space group by the Bravais lattice is a finite group which is one of the 32 possible point groups. Translation is defined as the moves from one point to another point. A glide plane is a reflection in a plane, followed by a parallel with that plane. This is noted by a, b or c, depending on which axis the glide is along. There is also the n glide, which is a glide along the half of a diagonal of a face, and the d glide, the latter is called the diamond glide plane as it features in the diamond structure. In 17 space groups, due to the centering of the cell, the glides occur in two directions simultaneously, i. e. the same glide plane can be called b or c, a or b. For example, group Abm2 could be also called Acm2, group Ccca could be called Cccb, in 1992, it was suggested to use symbol e for such planes. The symbols for five groups have been modified, A screw axis is a rotation about an axis. These are noted by a number, n, to describe the degree of rotation, the degree of translation is then added as a subscript showing how far along the axis the translation is, as a portion of the parallel lattice vector. So,21 is a rotation followed by a translation of 1/2 of the lattice vector
8.
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
9.
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
10.
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
11.
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
12.
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
13.
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
14.
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
15.
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
16.
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
17.
Dispersion (optics)
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In optics, dispersion is the phenomenon in which the phase velocity of a wave depends on its frequency. Media having this property may be termed dispersive media. Sometimes the term chromatic dispersion is used for specificity, the most familiar example of dispersion is probably a rainbow, in which dispersion causes the spatial separation of a white light into components of different wavelengths. Most often, chromatic dispersion refers to material dispersion, that is. However, in a waveguide there is also the phenomenon of waveguide dispersion, more generally, waveguide dispersion can occur for waves propagating through any inhomogeneous structure, whether or not the waves are confined to some region. In a waveguide, both types of dispersion will generally be present, although they are not strictly additive, for example, in fiber optics the material and waveguide dispersion can effectively cancel each other out to produce a zero-dispersion wavelength, important for fast fiber-optic communication. Material dispersion can be a desirable or undesirable effect in optical applications, the dispersion of light by glass prisms is used to construct spectrometers and spectroradiometers. Holographic gratings are used, as they allow more accurate discrimination of wavelengths. However, in lenses, dispersion causes chromatic aberration, an effect that may degrade images in microscopes, telescopes. The phase velocity, v, of a wave in a uniform medium is given by v = c n where c is the speed of light in a vacuum. In general, the index is some function of the frequency f of the light, thus n = n, or alternatively. The wavelength dependence of a refractive index is usually quantified by its Abbe number or its coefficients in an empirical formula such as the Cauchy or Sellmeier equations. In particular, for materials, the susceptibility χ that appears in the Kramers–Kronig relations is the electric susceptibility χe = n2 −1. The most commonly seen consequence of dispersion in optics is the separation of light into a color spectrum by a prism. From Snells law it can be seen that the angle of refraction of light in a prism depends on the index of the prism material. For visible light, refraction indices n of most transparent materials decrease with increasing wavelength λ,1 < n < n < n, or alternatively, in this case, the medium is said to have normal dispersion. Whereas, if the index increases with increasing wavelength, the medium is said to have anomalous dispersion, at the interface of such a material with air or vacuum, Snells law predicts that light incident at an angle θ to the normal will be refracted at an angle arcsin. Thus, blue light, with a refractive index, will be bent more strongly than red light
18.
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
19.
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
20.
Absorption spectroscopy
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Absorption spectroscopy refers to spectroscopic techniques that measure the absorption of radiation, as a function of frequency or wavelength, due to its interaction with a sample. The sample absorbs energy, i. e. photons, from the radiating field, the intensity of the absorption varies as a function of frequency, and this variation is the absorption spectrum. Absorption spectroscopy is performed across the electromagnetic spectrum, Infrared and ultraviolet-visible spectroscopy are particularly common in analytical applications. Absorption spectroscopy is employed in studies of molecular and atomic physics, astronomical spectroscopy. There are a range of experimental approaches for measuring absorption spectra. The most common arrangement is to direct a beam of radiation at a sample. The transmitted energy can be used to calculate the absorption, the source, sample arrangement and detection technique vary significantly depending on the frequency range and the purpose of the experiment. A materials absorption spectrum is the fraction of incident radiation absorbed by the material over a range of frequencies, the absorption spectrum is primarily determined by the atomic and molecular composition of the material. Radiation is more likely to be absorbed at frequencies that match the difference between two quantum mechanical states of the molecules. The absorption that occurs due to a transition between two states is referred to as a line and a spectrum is typically composed of many lines. The frequencies where absorption lines occur, as well as their relative intensities, primarily depend on the electronic, the frequencies will also depend on the interactions between molecules in the sample, the crystal structure in solids, and on several environmental factors. The lines will also have a width and shape that are determined by the spectral density or the density of states of the system. Absorption lines are classified by the nature of the quantum mechanical change induced in the molecule or atom. Rotational lines, for instance, occur when the state of a molecule is changed. Rotational lines are found in the microwave spectral region. Vibrational lines correspond to changes in the state of the molecule and are typically found in the infrared region. Electronic lines correspond to a change in the state of an atom or molecule and are typically found in the visible. X-ray absorptions are associated with the excitation of inner shell electrons in atoms and these changes can also be combined, leading to new absorption lines at the combined energy of the two changes
21.
Garnet
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Garnets are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. All species of garnets possess similar physical properties and crystal forms, the different species are pyrope, almandine, spessartine, grossular, uvarovite and andradite. The garnets make up two solid solution series, pyrope-almandine-spessartine and uvarovite-grossular-andradite, the word garnet comes from the 14th‑century Middle English word gernet, meaning dark red. It is derived from the Latin granatus, from granum, Garnet species are found in many colors including red, orange, yellow, green, purple, brown, blue, black, pink, and colorless, with reddish shades most common. Garnet species light transmission properties can range from the gemstone-quality transparent specimens to the varieties used for industrial purposes as abrasives. The minerals luster is categorized as vitreous or resinous, garnets are nesosilicates having the general formula X3Y23. The X site is occupied by divalent cations 2+ and the Y site by trivalent cations 3+ in an octahedral/tetrahedral framework with 4− occupying the tetrahedra. Garnets are most often found in the crystal habit, but are also commonly found in the trapezohedron habit. They crystallize in the system, having three axes that are all of equal length and perpendicular to each other. Garnets do not show cleavage, so when they fracture under stress, because the chemical composition of garnet varies, the atomic bonds in some species are stronger than in others. As a result, this group shows a range of hardness on the Mohs scale of about 6.5 to 7.5. The harder species like almandine are often used for abrasive purposes, for gem identification purposes, a pick-up response to a strong neodymium magnet separates garnet from all other natural transparent gemstones commonly used in the jewelry trade. Almandine, Fe3Al23 Pyrope, Mg3Al23 Spessartine, Mn3Al23 Almandine, sometimes incorrectly called almandite, is the modern gem known as carbuncle, the term carbuncle is derived from the Latin meaning live coal or burning charcoal. The name Almandine is a corruption of Alabanda, a region in Asia Minor where these stones were cut in ancient times, chemically, almandine is an iron-aluminium garnet with the formula Fe3Al23, the deep red transparent stones are often called precious garnet and are used as gemstones. Almandine occurs in metamorphic rocks like mica schists, associated with such as staurolite, kyanite, andalusite. Almandine has nicknames of Oriental garnet, almandine ruby, and carbuncle, Pyrope is red in color and chemically an aluminium silicate with the formula Mg3Al23, though the magnesium can be replaced in part by calcium and ferrous iron. The color of pyrope varies from red to black. A variety of pyrope from Macon County, North Carolina is a shade and has been called rhodolite
22.
Pliny the Elder
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In the latter number will be my uncle, by virtue of his own and of your compositions. Pliny is referring to the fact that Tacitus relied on his uncles now missing work on the History of the German Wars. The wind caused by the sixth and largest pyroclastic surge of the eruption would not allow his ship to leave the shore, and Pliny probably died during this event. Plinys dates are pinned to the eruption of Mount Vesuvius in AD79 and a statement of his nephew that he died in his 56th year, Pliny was the son of an equestrian, Gaius Plinius Celer, and his wife, Marcella. Neither the younger nor the elder Pliny mention the names and their ultimate source is a fragmentary inscription found in a field in Verona and recorded by the 16th century Augustinian monk Onofrio Panvinio at Verona. The reading of the inscription depends on the reconstruction, but in all cases the names come through, whether he was an augur and whether she was named Grania Marcella are less certain. Jean Hardouin presents a statement from a source that he claims was ancient, that Pliny was from Verona. Hardouin also cites the conterraneity of Catullus, additional efforts to connect Celer and Marcella with other gentes are highly speculative. Hardouin is the scholar to use his unknown source. He kept statues of his ancestors there, a statue of Pliny on the facade of the Duomo of Como celebrates him as a native son. He had a sister, Plinia, who married into the Caecilii and was the mother of his nephew, Pliny the Younger, whose letters describe his work and study regimen in detail. In one of his letters to Tacitus, Pliny the Younger details how his uncles breakfasts would be light and simple following the customs of our forefathers. This shows that Pliny the Younger wanted it to be conveyed that Pliny the Elder was a good Roman and this statement would have pleased Tacitus. Two inscriptions identifying the hometown of Pliny the Younger as Como take precedence over the Verona theory, one commemorates the youngers career as imperial magistrate and details his considerable charitable and municipal expenses on behalf of the people of Como. Another identifies his father Lucius village as Fecchio near Como and it is likely therefore that Plinia was a local girl and Pliny the Elder, her brother, was from Como. Gaius was a member of the Plinii gens and he did not take his fathers cognomen, Celer, but assumed his own, Secundus. As his adopted son took the same cognomen, Pliny founded a branch, no earlier instances of the Plinii are known. In 59 BC, only about 82 years before Plinys birth, Julius Caesar founded Novum Comum as a colonia to secure the region against the Alpine tribes, whom he had been unable to defeat
23.
Alabanda
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Alabanda or Antiochia of the Chrysaorians was an ancient city of Caria, Anatolia, the site of which is near Doğanyurt, Çine, Aydın Province, Turkey. The city is located in the saddle between two heights, the area is noted for its dark marble and for gemstones that resembled garnets. Stephanus of Byzantium claims that there were two cities named Alabanda in Caria, but no ancient source corroborates this. According to legend, the city was founded by a Carian hero Alabandus, in the Carian language, the name is a combination of the words for horse ala and victory banda. On one occasion, Herodotus mentions Alabanda being located in Phrygia, instead of in Caria, amyntas II, son of the Persian official Bubares, is known to have been given the rule over the city by king Xerxes I. In the early Seleucid period, the city was part of the Chrysaorian League, the city was renamed Antiochia of the Chrysaorians in honor of Seleucid king Antiochus III who preserved the citys peace. It was captured by Philip V of Macedon in 201 BC, the name reverted to Alabanda after the Seleucid defeat at the Battle of Magnesia in 190 BC. The Romans occupied the city shortly thereafter, according to Cicero in Greece they worshiped a number of deified human beings, at Alabanda there was Alabandus. In 40 BC, the rebel Quintus Labienus at the head of a Parthian army took the city, after Labienuss garrison was slaughtered by the citys inhabitants, the Parthian army stripped the city of its treasures. Under the Roman Empire, the city became a conventus and Strabo reports on its reputation for high-living, the city minted its own coins down to the mid-third century. During the Byzantine Empire, the city was a created a bishopric, famous residents included the orators Menecles and Hierocles, who were brothers. The ruins of Alabanda are 8 km west of Çine and consist of the remains of a theatre and a number of other buildings, the names of some bishops of Alabanda are known because of their participation in church councils. The names of two bishops of the see are also known, Zeuxis, who was deposed for Monophysitism in 518, and Julian. No longer a residential diocese, Alabanda is today listed by the Catholic Church as a titular see. J. Ma, Antiochos III and the Cities of Western Asia Minor, ISBN 978-0-19-815219-4, p.175 Hazlitts Classical Gazetteer Dictionary of Greek and Roman Geography at Perseus Project Briant, from Cyrus to Alexander, A History of the Persian Empire
24.
Caria
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Caria was a region of western Anatolia extending along the coast from mid-Ionia south to Lycia and east to Phrygia. The Ionian and Dorian Greeks colonized the west of it and joined the Carian population in forming Greek-dominated states there, the inhabitants of Caria, known as Carians, had arrived there before the Greeks. The Carians did speak an Anatolian language, known as Carian, cramers detailed catalog of Carian towns in classical Greece is based entirely on ancient sources. The multiple names of towns and geomorphic features, such as bays and headlands, coastal Caria begins with Didyma south of Miletus, but Miletus had been placed in the pre-Greek Caria. South of it is the Iassicus Sinus and the towns of Iassus and Bargylia, giving a name of Bargyleticus Sinus to Güllük Körfezi, and nearby Cindye. After Bargylia is Caryanda or Caryinda, and then on the Bodrum Peninsula Myndus,56 miles miles from Miletus, in the vicinity is Naziandus, exact location unknown. On the tip of the Bodrum Peninsula is Termera, and on the other side Ceramicus Sinus and it was formerly crowded with numerous towns. Halicarnassus, a Dorian Greek city, was planted there among six Carian towns, Theangela, Sibde, Medmasa, Euranium, Pedasa or Pedasum and these with Myndus and Synagela constitute the eight Lelege towns. Also on the north coast of the Ceramicus Sinus is Ceramus and Bargasus, on the south of the Ceramicus Sinus is the Carian Chersonnese, or Triopium Promontory, also called Doris after the Dorian colony of Cnidus. At the base of the peninsula is Bybassus or Bybastus from which an earlier names and it was now Acanthus and Doulopolis. South of the Carian Chersonnese is Doridis Sinus, the Gulf of Doris, there are three bays in it, Bubassius, Thymnias and Schoenus, the last enclosing the town of Hyda. In the gulf somewhere are Euthene or Eutane, Pitaeum, on the south shore is the Cynossema, or Onugnathos Promontory, opposite Symi. South of there is the Rhodian Peraea, a section of the coast under Rhodes and it includes Loryma or Larymna in Oedimus Bay, Gelos, Tisanusa, the headland of Paridion, Panydon or Pandion with Physicus, Amos, Physca or Physcus, also called Cressa. Beyond Cressa is the Calbis River, on the other side is Caunus, with Pisilis or Pilisis and Pyrnos between. Then follow some cities that some assign to Lydia and some to Caria, Calynda on the Indus River, Crya, Carya, Carysis or Cari and Alina in the Gulf of Glaucus, other Carian towns in the gulf are Clydae or Lydae and Aenus. At the base of the east end of Latmus near Euromus, the name Chrysaoris once applied to all of Caria, moreover, Euromus was originally settled from Lycia. Its towns are Tauropolis, Plarassa and Chrysaoris and these were all incorporated later into Mylasa. Connected to the latter by a way is Labranda
25.
Anatolia
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Anatolia, in geography known as Asia Minor, Asian Turkey, Anatolian peninsula, or Anatolian plateau, is the westernmost protrusion of Asia, which makes up the majority of modern-day Turkey. The region is bounded by the Black Sea to the north, the Mediterranean Sea to the south, the Sea of Marmara forms a connection between the Black and Aegean Seas through the Bosphorus and Dardanelles straits and separates Anatolia from Thrace on the European mainland. Traditionally, Anatolia is considered to extend in the east to a line between the Gulf of Alexandretta and the Black Sea to the Armenian Highlands, thus, traditionally Anatolia is the territory that comprises approximately the western two-thirds of the Asian part of Turkey. The Turkification of Anatolia began under the Seljuk Empire in the late 11th century, however, various non-Turkic languages continue to be spoken by minorities in Anatolia today, including Kurdish, Assyrian, Armenian, Arabic, Laz, Georgian, and Greek. Traditionally, Anatolia is considered to extend in the east to a line running from the Gulf of Alexandretta to the Black Sea. This traditional geographical definition is used, for example, in the latest edition of Merriam-Websters Geographical Dictionary, under this definition, Anatolia is bounded to the east by the Armenian Highlands, and the Euphrates before that river bends to the southeast to enter Mesopotamia. To the southeast, it is bounded by the ranges that separate it from the Orontes valley in Syria, the first name the Greeks used for the Anatolian peninsula was Ἀσία, presumably after the name of the Assuwa league in western Anatolia. As the name of Asia came to be extended to areas east of the Mediterranean. The name Anatolia derives from the Greek ἀνατολή meaning “the East” or more literally “sunrise”, the precise reference of this term has varied over time, perhaps originally referring to the Aeolian, Ionian and Dorian colonies on the west coast of Asia Minor. In the Byzantine Empire, the Anatolic Theme was a theme covering the western, the modern Turkish form of Anatolia is Anadolu, which again derives from the Greek name Aνατολή. The Russian male name Anatoly and the French Anatole share the same linguistic origin, in English the name of Turkey for ancient Anatolia first appeared c. It is derived from the Medieval Latin Turchia, which was used by the Europeans to define the Seljuk controlled parts of Anatolia after the Battle of Manzikert. Human habitation in Anatolia dates back to the Paleolithic, neolithic Anatolia has been proposed as the homeland of the Indo-European language family, although linguists tend to favour a later origin in the steppes north of the Black Sea. However, it is clear that the Anatolian languages, the oldest branch of Indo-European, have spoken in Anatolia since at least the 19th century BC. The earliest historical records of Anatolia stem from the southeast of the region and are from the Mesopotamian-based Akkadian Empire during the reign of Sargon of Akkad in the 24th century BC, scholars generally believe the earliest indigenous populations of Anatolia were the Hattians and Hurrians. The region was famous for exporting raw materials, and areas of Hattian-, one of the numerous cuneiform records dated circa 20th century BC, found in Anatolia at the Assyrian colony of Kanesh, uses an advanced system of trading computations and credit lines. They were speakers of an Indo-European language, the Hittite language, originating from Nesa, they conquered Hattusa in the 18th century BC, imposing themselves over Hattian- and Hurrian-speaking populations. According to the most widely accepted Kurgan theory on the Proto-Indo-European homeland, however, the Hittites adopted the cuneiform script, invented in Mesopotamia
26.
Cabochon
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A cabochon, from the Middle French word caboche, is a gemstone which has been shaped and polished as opposed to faceted. The resulting form is usually a convex obverse with a flat reverse, cutting en cabochon is usually applied to opaque gems, while faceting is usually applied to transparent stones. Hardness is also taken into account as softer gemstones with a lower than 7 on the Mohs hardness scale are easily scratched, mainly by silicon dioxide in dust. This would quickly make translucent gems unattractive—instead they are polished as cabochons, the usual shape for cutting cabochons is an ellipse. An exception is cabochons on some watches crowns, which are round, the procedure is to cut a slab of the rough rock with a slab saw, and next to stencil a shape from a template. The slab is then trimmed near the line using a diamond blade saw—called a trim saw. Diamond impregnated wheels or silicon carbide wheels can be used to grind the rock down. Most lapidary workshops and production facilities have moved away from silicon carbide to diamond grinding wheels or flat lap disks, once the piece is trimmed it can be dopped or completed by hand. Dopping is normally done by adhering the stone with hard wax onto a length of wooden dowel called a dop stick, the piece is then ground to the template line, the back edges may be bevelled, and finally the top is sanded and polished to a uniform dome
27.
Carbuncle (gemstone)
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A carbuncle /ˈkɑːrbʌŋkəl/ is any red gemstone, most often a red garnet. The word occurs in four places in many English translations of the Bible, for נֹפֶךְ itself they suggest the gloss semi-precious stone. Exodus 28,17 and 39,10 both refer to the use as the third stone in the breastplate of the Hoshen. Ezekiel 28,13 refers to the presence in the Garden of Eden. And I will make thy her windows of agates, and thy her gates of carbuncles, the gem is the stolen item in question in the Sherlock Holmes tale The Adventure of the Blue Carbuncle. A carbuncle plays a role in Nathaniel Hawthornes story, The Great Carbuncle. Hamlet by William Shakespeare refers to carbuncles in act 2 scene 2 line 401, With eyes like carbuncles, while its design ranges from a small, cute mammal to a large terrifying reptile, it always has a red gemstone on its forehead
28.
Optical spectrometer
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An optical spectrometer is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials. The variable measured is most often the lights intensity but could also, for instance, a spectrometer is used in spectroscopy for producing spectral lines and measuring their wavelengths and intensities. Spectrometers may also operate over a range of non-optical wavelengths. If the instrument is designed to measure the spectrum in absolute units rather than relative units, the majority of spectrophotometers are used in spectral regions near the visible spectrum. In general, any particular instrument will operate over a portion of this total range because of the different techniques used to measure different portions of the spectrum. Below optical frequencies, the analyzer is a closely related electronic device. Spectrometers are used in many fields, for example, they are used in astronomy to analyze the radiation from astronomical objects and deduce chemical composition. The spectrometer uses a prism or a grating to spread the light from a distant object into a spectrum and this allows astronomers to detect many of the chemical elements by their characteristic spectral fingerprints. If the object is glowing by itself, it will show spectral lines caused by the gas itself. These lines are named for the elements which cause them, such as the alpha, beta. Chemical compounds may also be identified by absorption, typically these are dark bands in specific locations in the spectrum caused by energy being absorbed as light from other objects passes through a gas cloud. Much of our knowledge of the makeup of the universe comes from spectra. Spectroscopes are often used in astronomy and some branches of chemistry, early spectroscopes were simply prisms with graduations marking wavelengths of light. Modern spectroscopes generally use a diffraction grating, a movable slit, Fraunhofer also went on to invent the first diffraction spectroscope. Gustav Robert Kirchhoff and Robert Bunsen discovered the application of spectroscopes to chemical analysis, Kirchhoff and Bunsens analysis also enabled a chemical explanation of stellar spectra, including Fraunhofer lines. When a material is heated to incandescence it emits light that is characteristic of the makeup of the material. Particular light frequencies give rise to sharply defined bands on the scale which can be thought of as fingerprints, in the original spectroscope design in the early 19th century, light entered a slit and a collimating lens transformed the light into a thin beam of parallel rays. The light then passed through a prism that refracted the beam into a spectrum because different wavelengths were refracted different amounts due to dispersion and this image was then viewed through a tube with a scale that was transposed upon the spectral image, enabling its direct measurement
29.
Absorption band
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According to quantum mechanics, atoms and molecules can only hold certain defined quantities of energy, or exist in specific states. An absorption band is a range of wavelengths, frequencies or energies in the spectrum which are characteristic of a particular transition from initial to final state in a substance. According to quantum mechanics, atoms and molecules can only hold certain defined quantities of energy, when electromagnetic radiation is absorbed by an atom or molecule, the energy of the radiation changes the state of the atom or molecule from an initial state to a final state. The number of states in an energy range is discrete for gaseous or diluted systems. Condensed systems, like liquids or solids, have a density of states distribution. In order for a substance to change its energy it must do so in a series of steps by the absorption of a photon and this absorption process can move a particle, like an electron, from an occupied state to an empty or unoccupied state. It can also move a whole vibrating or rotating system, like a molecule, when a photon is absorbed, the electromagnetic field of the photon disappears as it initiates a change in the state of the system that absorbs the photon. Energy, momentum, angular momentum, magnetic moment and electric dipole moment are transported from the photon to the system. Because there are laws, that have to be satisfied. This results in a series of selection rules and it is not possible to make any transition that lies within the energy or frequency range that is observed. The strength of an electromagnetic absorption process is determined by two factors. Second, not all transitions have the transition matrix element. For some types of bands or spectroscopic disciplines temperature and statistical mechanics plays an important role, for other energy ranges thermal motion effects, like Doppler broadening may determine the linewidth. A wide variety of band and line shapes exist. In many cases it is convenient to assume that a spectral line is a Lorentzian or Gaussian. Analysis of the density and the intensities, width and shape of spectral lines sometimes can yield a lot of information about the observed system like it is done with Mössbauer spectra. In systems with a large number of states like macromolecules. If the line broadening mechanism is known and the shape of spectral density is clearly visible in the spectrum
30.
Solid solution
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A solid solution is a solid-state solution of one or more solutes in a solvent. The solid solution needs to be distinguished from a mechanical mixtures of powdered solids like two salts, sugar and salt, etc, the mechanical mixtures have total or partial miscibility gap in solid state. Examples of solid solutions include crystallized salts from their liquid mixture, metal alloys, in the case of metal alloys intermetallic compounds occur frequently. The solute may incorporate into the solvent crystal lattice substitutionally, by replacing a solvent particle in the lattice, or interstitially, by fitting into the space between solvent particles. Both of these types of solid solution affect the properties of the material by distorting the crystal lattice, some mixtures will readily form solid solutions over a range of concentrations, while other mixtures will not form solid solutions at all. The propensity for any two substances to form a solution is a complicated matter involving the chemical, crystallographic. 1 displays an alloy of two metals which forms a solution at all relative concentrations of the two species. Solid solutions have important commercial and industrial applications, as such mixtures often have superior properties to pure materials, many metal alloys are solid solutions. Even small amounts of solute can affect the electrical and physical properties of the solvent, the binary phase diagram in Fig.2 shows the phases of a mixture of two substances in varying concentrations, A and B. The region labeled α is a solution, with B acting as the solute in a matrix of A. On the other end of the scale, the region labeled β is also a solid solution. The large solid region in between the α and β solid solutions, labeled α + β, is not a solid solution, at other proportions, the material will enter a mushy or pasty phase until it warms up to being completely melted. The mixture at the dip point of the diagram is called a eutectic alloy, lead-tin mixtures formulated at that point are useful when soldering electronic components, particularly if done manually, since the solid phase is quickly entered as the solder cools. In contrast, when lead-tin mixtures were used to solder seams in automobile bodies a pasty state enabled a shape to be formed with a paddle or tool. When a solid solution becomes unstable — due to a temperature, for example — exsolution occurs. This is mainly caused by difference in cation size, cations which have a large difference in radii are not likely to readily substitute. Take the alkali feldspar minerals for example, whose end members are albite, NaAlSi3O8 and microcline and this leads to exsolution where they will separate into two separate phases. In the case of the feldspar minerals, thin white albite layers will alternate between typically pink microcline
31.
Pyrope
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The mineral pyrope is a member of the garnet group. Pyrope is the member of the garnet family to always display red colouration in natural samples. Despite being less common than most garnets, it is a widely used gemstone with numerous alternative names, chrome pyrope, and Bohemian garnet are two alternative names, the usage of the latter being discouraged by the Gemological Institute of America. Misnomers include Colorado ruby, Arizona ruby, California ruby, Rocky Mountain ruby, Elie Ruby, Bohemian carbuncle, the composition of pure pyrope is Mg3Al23, although typically other elements are present in at least minor proportions—these other elements include Ca, Cr, Fe and Mn. Pyrope forms a solid solution series with almandine and spessartine, which are known as the pyralspite garnets. Iron and manganese substitute for the magnesium in the pyrope structure, the resultant, mixed composition garnets are defined according to their pyrope-almandine ratio. The semi-precious stone rhodolite is a garnet of ~70% pyrope composition, the origin of most pyrope is in ultramafic rocks, typically peridotite from the Earths mantle, these mantle-derived peridotites can be attributed both to igneous and metamorphic processes. Pyrope also occurs in metamorphic rocks, as in the Dora-Maira massif in the western Alps. In that massif, nearly pure pyrope occurs in crystals to almost 12 cm in diameter, some of that pyrope has inclusions of coesite, pyrope is common in peridotite xenoliths from kimberlite pipes, some of which are diamond-bearing. These varieties are known as chrome-pyrope, or G9/G10 garnets, in hand specimen, pyrope is very tricky to distinguish from almandine, however it is likely to display fewer flaws and inclusions. Other distinguishing criteria are listed in the adjacent table, care should be taken when using these properties as many of those listed have been determined from synthetically grown, pure-composition pyrope. Others, such as pyropes high specific gravity, may be of use when studying a small crystal embedded in a matrix of other silicate minerals. In these cases, mineral association with other mafic and ultramafic minerals may be the best indication that the garnet you are studying is pyrope, in petrographic thin section, the most distinguishing features of pyrope are those shared with the other common garnets, high relief and isotropy. Garnets tend to be less strongly coloured than other silicate minerals in thin section, the lack of cleavage, commonly euhedral crystal morphology, and mineral associations should also be used in identification of pyrope under the microscope. STEHLÍKOVÁ, Dana, The Bohemian Garnet,1
32.
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
33.
Iron
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Iron is a chemical element with symbol Fe and atomic number 26. It is a metal in the first transition series and it is by mass the most common element on Earth, forming much of Earths outer and inner core. It is the fourth most common element in the Earths crust, like the other group 8 elements, ruthenium and osmium, iron exists in a wide range of oxidation states, −2 to +6, although +2 and +3 are the most common. Elemental iron occurs in meteoroids and other low oxygen environments, but is reactive to oxygen, fresh iron surfaces appear lustrous silvery-gray, but oxidize in normal air to give hydrated iron oxides, commonly known as rust. Unlike the metals that form passivating oxide layers, iron oxides occupy more volume than the metal and thus flake off, Iron metal has been used since ancient times, although copper alloys, which have lower melting temperatures, were used even earlier in human history. Pure iron is soft, but is unobtainable by smelting because it is significantly hardened and strengthened by impurities, in particular carbon. A certain proportion of carbon steel, which may be up to 1000 times harder than pure iron. Crude iron metal is produced in blast furnaces, where ore is reduced by coke to pig iron, further refinement with oxygen reduces the carbon content to the correct proportion to make steel. Steels and iron alloys formed with metals are by far the most common industrial metals because they have a great range of desirable properties. Iron chemical compounds have many uses, Iron oxide mixed with aluminium powder can be ignited to create a thermite reaction, used in welding and purifying ores. Iron forms binary compounds with the halogens and the chalcogens, among its organometallic compounds is ferrocene, the first sandwich compound discovered. Iron plays an important role in biology, forming complexes with oxygen in hemoglobin and myoglobin. Iron is also the metal at the site of many important redox enzymes dealing with cellular respiration and oxidation and reduction in plants. A human male of average height has about 4 grams of iron in his body and this iron is distributed throughout the body in hemoglobin, tissues, muscles, bone marrow, blood proteins, enzymes, ferritin, hemosiderin, and transport in plasma. The mechanical properties of iron and its alloys can be evaluated using a variety of tests, including the Brinell test, Rockwell test, the data on iron is so consistent that it is often used to calibrate measurements or to compare tests. An increase in the content will cause a significant increase in the hardness. Maximum hardness of 65 Rc is achieved with a 0. 6% carbon content, because of the softness of iron, it is much easier to work with than its heavier congeners ruthenium and osmium. Because of its significance for planetary cores, the properties of iron at high pressures and temperatures have also been studied extensively
34.
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
35.
Crust (geology)
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In geology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle. The crust of the Earth is composed of a variety of igneous, metamorphic. The crust is underlain by the mantle, the upper part of the mantle is composed mostly of peridotite, a rock denser than rocks common in the overlying crust. The boundary between the crust and mantle is conventionally placed at the Mohorovičić discontinuity, a boundary defined by a contrast in seismic velocity, the crust occupies less than 1% of Earths volume. The crust of the Earth is of two types, oceanic and continental. The oceanic crust is 5 km to 10 km thick and is composed primarily of basalt, diabase, the continental crust is typically from 30 km to 50 km thick and is mostly composed of slightly less dense rocks than those of the oceanic crust. Some of these less dense rocks, such as granite, are common in the continental crust, both the continental and oceanic crust float on the mantle. Because the continental crust is thicker, it both to greater elevations and greater depth than the oceanic crust. The slightly lower density of continental rock compared to basaltic oceanic rock contributes to the higher relative elevation of the top of the continental crust. As the top of the continental crust reaches elevations higher than that of the oceanic, the temperature of the crust increases with depth, reaching values typically in the range from about 200 °C to 400 °C at the boundary with the underlying mantle. The crust and underlying relatively rigid uppermost mantle make up the lithosphere, because of convection in the underlying plastic upper mantle and asthenosphere, the lithosphere is broken into tectonic plates that move. The temperature increases by as much as 30 °C for every kilometer locally in the part of the crust. Earth has probably always had some form of basaltic crust, in contrast, the bulk of the continental crust is much older. The oldest continental crustal rocks on Earth have ages in the range from about 3.7 to 4, some zircon with age as great as 4.3 billion years has been found in the Narryer Gneiss Terrane. The average age of the current Earths continental crust has been estimated to be about 2.0 billion years, most crustal rocks formed before 2.5 billion years ago are located in cratons. Such old continental crust and the underlying mantle asthenosphere are less dense than elsewhere in Earth, formation of new continental crust is linked to periods of intense orogeny, these periods coincide with the formation of the supercontinents such as Rodinia, Pangaea and Gondwana. The continental crust has a composition similar to that of andesite. The most abundant minerals in Earths continental crust are feldspars, which make up about 41% of the crust by weight, followed by quartz at 12%, Continental crust is enriched in incompatible elements compared to the basaltic ocean crust and much enriched compared to the underlying mantle
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Upper mantle
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The mantle is a layer inside a terrestrial planet and some other rocky planetary bodies. For a mantle to form, the body must be large enough to have undergone the process of planetary differentiation by density. The mantle surrounds the planetary core, the mantle is surrounded by the crust. The terrestrial planets, the Moon, two of Jupiters moons and the asteroid Vesta each have a made of silicate rock. Interpretation of spacecraft data suggests that at least two moons of Jupiter, as well as Titan and Triton each have a mantle made of ice or other solid volatile substances. The interior of Earth, similar to the terrestrial planets, is divided into layers of different composition. The mantle is a layer between the crust and the outer core, Earths mantle is a silicate rocky shell with an average thickness of 2,886 kilometres. The mantle makes up about 84% of Earths volume and it is predominantly solid but in geological time it behaves as a very viscous fluid. The mantle encloses the hot core rich in iron and nickel, past episodes of melting and volcanism at the shallower levels of the mantle have produced a thin crust of crystallized melt products near the surface. A thin crust, the part of the lithosphere, surrounds the mantle and is about 5 to 75 km thick. In some places under the ocean the mantle is exposed on the surface of Earth. The mantle is divided into sections which are based upon results from seismology and these layers are the following, the upper mantle, the transition zone, the lower mantle, and anomalous core–mantle boundary with a variable thickness. The uppermost mantle plus overlying crust are relatively rigid and form the lithosphere, below the lithosphere the upper mantle becomes notably more plastic. In some regions below the lithosphere, the shear velocity is reduced. Inge Lehmann discovered a seismic discontinuity at about 220 km depth, although this discontinuity has been found in other studies, the transition zone is an area of great complexity, it physically separates the upper and lower mantle. Very little is known about the lower mantle apart from that it appears to be relatively seismically homogeneous, the D layer at the core–mantle boundary separates the mantle from the core. A principal source of the heat that drives plate tectonics is the decay of uranium, thorium. The mantle differs substantially from the crust in its properties as the direct consequence of the difference in composition
37.
Antiferromagnetism
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This is, like ferromagnetism and ferrimagnetism, a manifestation of ordered magnetism. Generally, antiferromagnetic order may exist at low temperatures, vanishing at and above a certain temperature. Above the Néel temperature, the material is typically paramagnetic, when no external field is applied, the antiferromagnetic structure corresponds to a vanishing total magnetization. Although the net magnetization should be zero at a temperature of absolute zero, the magnetic susceptibility of an antiferromagnetic material typically shows a maximum at the Néel temperature. In contrast, at the transition between the ferromagnetic to the paramagnetic phases the susceptibility will diverge, in the antiferromagnetic case, a divergence is observed in the staggered susceptibility. Various microscopic interactions between the magnetic moments or spins may lead to antiferromagnetic structures, in the simplest case, one may consider an Ising model on a bipartite lattice, e. g. the simple cubic lattice, with couplings between spins at nearest neighbor sites. Depending on the sign of that interaction, ferromagnetic or antiferromagnetic order will result, geometrical frustration or competing ferro- and antiferromagnetic interactions may lead to different and, perhaps, more complicated magnetic structures. Antiferromagnetic materials occur commonly among transition metal compounds, especially oxides, examples include hematite, metals such as chromium, alloys such as iron manganese, and oxides such as nickel oxide. There are also numerous examples among high nuclearity metal clusters, organic molecules can also exhibit antiferromagnetic coupling under rare circumstances, as seen in radicals such as 5-dehydro-m-xylylene. Unlike ferromagnetism, anti-ferromagnetic interactions can lead to multiple optimal states, in one dimension, the anti-ferromagnetic ground state is an alternating series of spins, up, down, up, down, etc. Yet in two dimensions, multiple ground states can occur, consider an equilateral triangle with three spins, one on each vertex. If each spin can take on two values, there are 23 =8 possible states of the system, six of which are ground states. The two situations which are not ground states are all three spins are up or are all down. In any of the six states, there will be two favorable interactions and one unfavorable one. This illustrates frustration, the inability of the system to find a ground state. This type of behavior has been found in minerals that have a crystal stacking structure such as a Kagome lattice or hexagonal lattice. Synthetic antiferromagnets are artificial antiferromagnets consisting of two or more thin ferromagnetic layers separated by a nonmagnetic layer, due to dipole coupling of the ferromagnetic layers results in antiparallel alignment of the magnetization of the ferromagnets. Antiferromagnetism plays a role in giant magnetoresistance, as had been discovered in 1988 by the Nobel prize winners Albert Fert
38.
Sri Lanka
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Sri Lanka, officially the Democratic Socialist Republic of Sri Lanka, is an island country in South Asia near south-east India. Sri Lanka has maritime borders with India to the northwest and the Maldives to the southwest, Sri Lankas documented history spans 3,000 years, with evidence of pre-historic human settlements dating back to at least 125,000 years. Its geographic location and deep harbours made it of strategic importance from the time of the ancient Silk Road through to World War II. Sri Lanka was known from the beginning of British colonial rule until 1972 as Ceylon, Sri Lankas recent history has been marred by a thirty-year civil war which decisively ended when the Sri Lankan military defeated the Liberation Tigers of Tamil Eelam in 2009. A diverse and multicultural country, Sri Lanka is home to many religions, ethnic groups, in addition to the majority Sinhalese, it is home to large groups of Sri Lankan and Indian Tamils, Moors, Burghers, Malays, Kaffirs and the aboriginal Vedda. Sri Lanka has a rich Buddhist heritage, and the first known Buddhist writings of Sri Lanka, Sri Lanka is a republic and a unitary state governed by a semi-presidential system. The legislative capital, Sri Jayawardenepura Kotte, is a suburb of the capital and largest city. Along with the Maldives, Sri Lanka is one of the two countries in South Asia that are rated among high human development on the Human Development Index. In antiquity, Sri Lanka was known to travellers by a variety of names, according to the Mahavamsa, the legendary Prince Vijaya named the land Tambapanni, because his followers hands were reddened by the red soil of the area. In Hindu mythology, such as the Mahabharata, the island was referred to as Lankā, in Tamil, the island is referred to as Eelam. Ancient Greek geographers called it Taprobanā or Taprobanē from the word Tambapanni, as a British crown colony, the island was known as Ceylon, it achieved independence as the Dominion of Ceylon in 1948. The country is known in Sinhalese as Śrī Laṃkā and in Tamil as Ilaṅkai, in 1972, its formal name was changed to Free, Sovereign and Independent Republic of Sri Lanka. Later in 1978 it was changed to the Democratic Socialist Republic of Sri Lanka, as the name Ceylon still appears in the names of a number of organisations, the Sri Lankan government announced in 2011 a plan to rename all those over which it has authority. The pre-history of Sri Lanka goes back 125,000 years, the era spans the Palaeolithic, Mesolithic and early Iron Ages. Among the Paleolithic human settlements discovered in Sri Lanka, Pahiyangala and it is said that Kubera was overthrown by his demon stepbrother Ravana, the powerful emperor who built a mythical flying machine named Dandu Monara. The modern city of Wariyapola is described as Ravanas airport, early inhabitants of Sri Lanka were probably ancestors of the Vedda people, an indigenous people numbering approximately 2,500 living in modern-day Sri Lanka. According to the Mahāvamsa, a written in Pāḷi, the original inhabitants of Sri Lanka are the Yakshas and Nagas. Ancient cemeteries that were used before 600BC and other signs of advanced civilization has also discovered in Sri Lanka
39.
Bago, Myanmar
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Bago, formerly known as Hanthawaddy, is a city and the capital of the Bago Region in Myanmar. It is located 50 miles north-east of Yangon, the Gulf of Martaban was colonized by Mon people from the Thaton Kingdom, who established Bago. In 825, the twin brothers Samala and Vimala founded Pegu, the earliest mention of Bago in history is by the Arab geographer ibn Khordadbeh around 850 AD. At the time, the Mon capital had shifted to Thaton, the area came under rule of the Burmese from Bagan in 1056. After the collapse of Bagan to the Mongols in 1287, the Mon regained their independence, in Lower Burma, a Mon dynasty established itself first at Mottama and then at Bago. During the reign of King Razadarit, Bago and Ava Kingdom were engaged in the Forty Years War, the peaceful reign of Queen Shin Sawbu came to an end when she chose the Buddhist monk Dhammazedi to succeed her. Under Dhammazedi, Bago became a centre of commerce and Theravada Buddhism, from 1353–1539, Binnya U, descendant of the Thai chief Wareru, established Hanthawaddy as the capital of the Mon Hanthawaddy Kingdom, which covered all of what is now Lower Burma. The area came under Burman control again in 1539, when it was annexed by King Tabinshwehti of the Taungoo Dynasty, the kings of Taungoo made Bago their royal capital from 1539–1599 and again in 1613–1635, and used it as a base for repeated invasions of the Ayutthaya Kingdom. In 1519, António Correia, then a merchant from the Portuguese casados settlement at Cochin landed in Bago, then known to the Portuguese as Pegu, a year later, Portuguese India Governor Diogo Lopes de Sequeira sent an ambassador to Pegu. As a major seaport, the city was visited by Europeans, among these. The Europeans often commented on its magnificence, the capital was looted by the viceroy of Toungoo, Minye Thihathu II of Toungoo, and then burned by the viceroy of Arakin during the Burmese–Siamese War. Anaukpetlun wanted to rebuild Hongsawadi, which had been deserted since Nanda Bayin had abandoned it and he was only able to build a temporary palace, however. The Burmese capital relocated to Ava in 1634, in 1740, the Mon revolted and founded the Restored Hanthawaddy Kingdom. However, a Bamar king, Alaungpaya, captured the city in May 1757, Bago was rebuilt by King Bodawpaya, but by then the river had shifted course, cutting the city off from the sea. It never regained its previous importance, after the Second Anglo-Burmese War, the British annexed Bago in 1852. In 1862, the province of British Burma was formed, the substantial differences between the colloquial and literary pronunciations, as with Burmese words, was a reason of the British corruption Pegu. In 1911, Hanthawaddy was described as a district in the Bago division of Lower Burma and it lay in the home district of Yangon, from which the town was detached to make a separate district in 1880. It had an area of 3,023 square miles, with a population of 48,411 in 1901, Hanthawaddy and Hinthada were the two most densely populated districts in the province
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Myanmar
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Myanmar, officially the Republic of the Union of Myanmar and also known as Burma, is a sovereign state in South East Asia bordered by Bangladesh, India, China, Laos and Thailand. About one third of Myanmars total perimeter of 5,876 km, forms an uninterrupted coastline of 1,930 km along the Bay of Bengal, the countrys 2014 census revealed a much lower population than expected, with 51 million people recorded. Myanmar is 676,578 square kilometres in size and its capital city is Naypyidaw and its largest city and former capital city is Yangon. Early civilizations in Myanmar included the Tibeto-Burman-speaking Pyu city-states in Upper Burma, the Pagan Kingdom fell due to the Mongol invasions and several warring states emerged. In the 16th century, reunified by the Taungoo Dynasty, the country was for a period the largest empire in the history of Mainland Southeast Asia. The early 19th century Konbaung Dynasty ruled over an area included modern Myanmar and briefly controlled Manipur. The British invaded Myanmar after three Anglo-Burmese Wars in the 19th century and the became a British colony. Myanmar became an independent nation in 1948, initially as a nation and then, following a coup détat in 1962. For most of its independent years, the country has been engrossed in rampant ethnic strife, during this time, the United Nations and several other organisations have reported consistent and systematic human rights violations in the country. In 2011, the junta was officially dissolved following a 2010 general election. While former military leaders still wield enormous power in the country, there is, however, continuing criticism of the governments treatment of the Muslim Rohingya minority and its poor response to the religious clashes. In the landmark 2015 election, Aung San Suu Kyis party won a majority in both houses, Myanmar is a country rich in jade and gems, oil, natural gas and other mineral resources. In 2013, its GDP stood at US$56.7 billion, the income gap in Myanmar is among the widest in the world, as a large proportion of the economy is controlled by supporters of the former military government. As of 2016, according to the Human Development Index, Myanmar had a level of human development. The renaming remains a contested issue, many political and ethnic opposition groups and countries continue to use Burma because they do not recognise the legitimacy of the ruling military government or its authority to rename the country. The countrys official name is the Republic of the Union of Myanmar. Countries that do not officially recognise that name use the long form Union of Burma instead, in English, the country is popularly known as either Burma or Myanmar /ˈmjɑːnˌmɑːr/. Both these names are derived from the name of the majority Burmese Bamar ethnic group, Myanmar is considered to be the literary form of the name of the group, while Burma is derived from Bamar, the colloquial form of the groups name
41.
Northern Territory
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The Northern Territory is a federal Australian territory in the central and central northern regions of Australia. It shares borders with Western Australia to the west, South Australia to the south, to the north, the territory is bordered by the Timor Sea, the Arafura Sea and the Gulf of Carpentaria. Despite its large area—over 1,349,129 square kilometres, the Northern Territorys population of 244,000 makes it the least populous of Australias eight major states and territories, having fewer than half as many people as Tasmania. The archaeological history of the Northern Territory begins over 40,000 years ago when Indigenous Australians settled the region, makassan traders began trading with the indigenous people of the Northern Territory for trepang from at least the 18th century onwards. The coast of the territory was first seen by Europeans in the 17th century, the British were the first Europeans to attempt to settle the coastal regions. After three failed attempts to establish a settlement, success was achieved in 1869 with the establishment of a settlement at Port Darwin. Today the economy is based on tourism, especially Kakadu National Park in the Top End and the Uluru-Kata Tjuta National Park in central Australia, the capital and largest city is Darwin. The population is not concentrated in regions but rather along the Stuart Highway. The other major settlements are Palmerston, Alice Springs, Katherine, Nhulunbuy, residents of the Northern Territory are often known simply as Territorians and fully as Northern Territorians, or more informally as Top Enders and Centralians. With the coming of the British, there were four attempts to settle the harsh environment of the northern coast. The Northern Territory was part of colonial New South Wales from 1825 to 1863, except for a time from February to December 1846. It was part of South Australia from 1863 to 1911, under the administration of colonial South Australia, the overland telegraph was constructed between 1870 and 1872. A railway was built between Palmerston and Pine Creek between 1883 and 1889. The economic pattern of raising and mining was established so that by 1911 there were 513,000 cattle. Victoria River Downs was at one time the largest cattle station in the world, gold was found at Grove Hill in 1872 and at Pine Creek, Brocks Creek, Burrundi, and copper was found at Daly River. On 1 January 1911, a decade after federation, the Northern Territory was separated from South Australia, alfred Deakin opined at this time To me the question has been not so much commercial as national, first, second, third and last. Either we must accomplish the peopling of the territory or submit to its transfer to some other nation. In late 1912 there was growing sentiment that the name Northern Territory was unsatisfactory, the names Kingsland, Centralia and Territoria were proposed with Kingsland becoming the preferred choice in 1913
42.
Australia
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Australia, officially the Commonwealth of Australia, is a country comprising the mainland of the Australian continent, the island of Tasmania and numerous smaller islands. It is the worlds sixth-largest country by total area, the neighbouring countries are Papua New Guinea, Indonesia and East Timor to the north, the Solomon Islands and Vanuatu to the north-east, and New Zealand to the south-east. Australias capital is Canberra, and its largest urban area is Sydney, for about 50,000 years before the first British settlement in the late 18th century, Australia was inhabited by indigenous Australians, who spoke languages classifiable into roughly 250 groups. The population grew steadily in subsequent decades, and by the 1850s most of the continent had been explored, on 1 January 1901, the six colonies federated, forming the Commonwealth of Australia. Australia has since maintained a liberal democratic political system that functions as a federal parliamentary constitutional monarchy comprising six states. The population of 24 million is highly urbanised and heavily concentrated on the eastern seaboard, Australia has the worlds 13th-largest economy and ninth-highest per capita income. With the second-highest human development index globally, the country highly in quality of life, health, education, economic freedom. The name Australia is derived from the Latin Terra Australis a name used for putative lands in the southern hemisphere since ancient times, the Dutch adjectival form Australische was used in a Dutch book in Batavia in 1638, to refer to the newly discovered lands to the south. On 12 December 1817, Macquarie recommended to the Colonial Office that it be formally adopted, in 1824, the Admiralty agreed that the continent should be known officially as Australia. The first official published use of the term Australia came with the 1830 publication of The Australia Directory and these first inhabitants may have been ancestors of modern Indigenous Australians. The Torres Strait Islanders, ethnically Melanesian, were originally horticulturists, the northern coasts and waters of Australia were visited sporadically by fishermen from Maritime Southeast Asia. The first recorded European sighting of the Australian mainland, and the first recorded European landfall on the Australian continent, are attributed to the Dutch. The first ship and crew to chart the Australian coast and meet with Aboriginal people was the Duyfken captained by Dutch navigator, Willem Janszoon. He sighted the coast of Cape York Peninsula in early 1606, the Dutch charted the whole of the western and northern coastlines and named the island continent New Holland during the 17th century, but made no attempt at settlement. William Dampier, an English explorer and privateer, landed on the north-west coast of New Holland in 1688, in 1770, James Cook sailed along and mapped the east coast, which he named New South Wales and claimed for Great Britain. The first settlement led to the foundation of Sydney, and the exploration, a British settlement was established in Van Diemens Land, now known as Tasmania, in 1803, and it became a separate colony in 1825. The United Kingdom formally claimed the part of Western Australia in 1828. Separate colonies were carved from parts of New South Wales, South Australia in 1836, Victoria in 1851, the Northern Territory was founded in 1911 when it was excised from South Australia
43.
Dodecahedron
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In geometry, a dodecahedron is any polyhedron with twelve flat faces. The most familiar dodecahedron is the dodecahedron, which is a Platonic solid. There are also three regular star dodecahedra, which are constructed as stellations of the convex form, all of these have icosahedral symmetry, order 120. The pyritohedron is a pentagonal dodecahedron, having the same topology as the regular one. The rhombic dodecahedron, seen as a case of the pyritohedron has octahedral symmetry. The elongated dodecahedron and trapezo-rhombic dodecahedron variations, along with the rhombic dodecahedra are space-filling, there are a large number of other dodecahedra. The convex regular dodecahedron is one of the five regular Platonic solids, the dual polyhedron is the regular icosahedron, having five equilateral triangles around each vertex. Like the regular dodecahedron, it has twelve pentagonal faces. However, the pentagons are not constrained to be regular, and its 30 edges are divided into two sets – containing 24 and 6 edges of the same length. The only axes of symmetry are three mutually perpendicular twofold axes and four threefold axes. Note that the regular dodecahedron can occur as a shape for quasicrystals with icosahedral symmetry. Its name comes from one of the two common crystal habits shown by pyrite, the one being the cube. The coordinates of the eight vertices of the cube are, The coordinates of the 12 vertices of the cross-edges are. When h =1, the six cross-edges degenerate to points, when h =0, the cross-edges are absorbed in the facets of the cube, and the pyritohedron reduces to a cube. When h = √5 − 1/2, the inverse of the golden ratio, a reflected pyritohedron is made by swapping the nonzero coordinates above. The two pyritohedra can be superimposed to give the compound of two dodecahedra as seen in the image here, the regular dodecahedron represents a special intermediate case where all edges and angles are equal. A tetartoid is a dodecahedron with chiral tetrahedral symmetry, like the regular dodecahedron, it has twelve identical pentagonal faces, with three meeting in each of the 20 vertices. However, the pentagons are not regular and the figure has no fivefold symmetry axes, although regular dodecahedra do not exist in crystals, the tetartoid form does
One or more of the preceding sentences incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Almandine". Encyclopædia Britannica. 1 (11th ed.). Cambridge University Press. p. 712.
One or more of the preceding sentences incorporates text from a publication now in the 
