1.
Magaliesburg
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Magaliesburg is a small town situated below the Witwatersrand mountain range in Gauteng, South Africa. The Magaliesberg mountain range is north and visible from town, hence the name Magaliesburg, burg is the Afrikaans name for Town whereas Berg is for mountain. The town and surrounds are popular holiday and weekend destinations for the residents of Johannesburg, with more than 100 accommodation venues and a great variety of activities, this small village at the foot of the Magalies Mountain is the ideal escape for city dwellers. Magaliesburg is the home of the oldest mine in Gauteng, at The Blaauwbank mine gold was discovered there more than 100 years ago. Besides tourism, the income generating activity of Magaliesburg and the surrounding area is agriculture. Beef, Maize, and large scale vegetable farming are most prevalent, the village has become a very attractive option for city dwellers who wish to live closer to nature. Homesteading is popular with individuals and families going out of their way to be as self-sufficient as they are able. As this is a difficult goal for most, there are many Magaliesburgers who live in the area. Media related to Magaliesburg at Wikimedia Commons
2.
Oxide minerals
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The oxide mineral class includes those minerals in which the oxide anion is bonded to one or more metal ions. The hydroxide bearing minerals are typically included in the oxide class, the minerals with complex anion groups such as the silicates, sulfates, carbonates and phosphates are classed separately. This list uses it to modify the Classification of Nickel–Strunz,00 Clinobirnessite*,00 Kleberite*,00 Chubutite*,00 Struverite
3.
Chemical formula
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These are limited to a single typographic line of symbols, which may include subscripts and superscripts. A chemical formula is not a name, and it contains no words. Although a chemical formula may imply certain simple chemical structures, it is not the same as a full chemical structural formula. Chemical formulas can fully specify the structure of only the simplest of molecules and chemical substances, the simplest types of chemical formulas are called empirical formulas, which use letters and numbers indicating the numerical proportions of atoms of each type. Molecular formulas indicate the numbers of each type of atom in a molecule. For example, the formula for glucose is CH2O, while its molecular formula is C6H12O6. This is possible if the relevant bonding is easy to show in one dimension, an example is the condensed molecular/chemical formula for ethanol, which is CH3-CH2-OH or CH3CH2OH. For reasons of structural complexity, there is no condensed chemical formula that specifies glucose, chemical formulas may be used in chemical equations to describe chemical reactions and other chemical transformations, such as the dissolving of ionic compounds into solution. A chemical formula identifies each constituent element by its chemical symbol, in empirical formulas, these proportions begin with a key element and then assign numbers of atoms of the other elements in the compound, as ratios to the key element. For molecular compounds, these numbers can all be expressed as whole numbers. For example, the formula of ethanol may be written C2H6O because the molecules of ethanol all contain two carbon atoms, six hydrogen atoms, and one oxygen atom. Some types of compounds, however, cannot be written with entirely whole-number empirical formulas. An example is boron carbide, whose formula of CBn is a variable non-whole number ratio with n ranging from over 4 to more than 6.5. When the chemical compound of the consists of simple molecules. These types of formulas are known as molecular formulas and condensed formulas. A molecular formula enumerates the number of atoms to reflect those in the molecule, so that the formula for glucose is C6H12O6 rather than the glucose empirical formula. However, except for very simple substances, molecular chemical formulas lack needed structural information, for simple molecules, a condensed formula is a type of chemical formula that may fully imply a correct structural formula. For example, ethanol may be represented by the chemical formula CH3CH2OH
4.
Silicon
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Silicon is a chemical element with symbol Si and atomic number 14. A hard and brittle crystalline solid with a metallic luster. It is a member of group 14 in the table, along with carbon above it and germanium, tin, lead. It is not very reactive, although more reactive than germanium, Silicon is the eighth most common element in the universe by mass, but very rarely occurs as the pure element in the Earths crust. It is most widely distributed in dusts, sands, planetoids, over 90% of the Earths crust is composed of silicate minerals, making silicon the second most abundant element in the Earths crust after oxygen. Most silicon is used commercially without being separated, and often with little processing of the natural minerals, such use includes industrial construction with clays, silica sand, and stone. Silicate is used in Portland cement for mortar and stucco, and mixed with sand and gravel to make concrete for walkways, foundations. Silicates are used in whiteware ceramics such as porcelain, and in traditional quartz-based soda-lime glass, Silicon compounds such as silicon carbide are used as abrasives and components of high-strength ceramics. Elemental silicon also has an impact on the modern world economy. Most free silicon is used in the refining, aluminium-casting. Silicon is the basis of the widely used synthetic polymers called silicones, Silicon is an essential element in biology, although only tiny traces are required by animals. However, various sea sponges and microorganisms, such as diatoms and radiolaria, silica is deposited in many plant tissues, such as in the bark and wood of Chrysobalanaceae and the silica cells and silicified trichomes of Cannabis sativa, horsetails and many grasses. Silicon is a solid at room temperature, with a point of 1,414 °C. Like water, it has a density in a liquid state than in a solid state and it expands when it freezes. With a relatively high conductivity of 149 W·m−1·K−1, silicon conducts heat well. In its crystalline form, pure silicon has a gray color, like germanium, silicon is rather strong, very brittle, and prone to chipping. Silicon, like carbon and germanium, crystallizes in a cubic crystal structure with a lattice spacing of 0.5430710 nm. The outer electron orbital of silicon, like that of carbon, has four valence electrons, the 1s, 2s, 2p and 3s subshells are completely filled while the 3p subshell contains two electrons out of a possible six
5.
Oxygen
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Oxygen is a chemical element with symbol O and atomic number 8. It is a member of the group on the periodic table and is a highly reactive nonmetal. By mass, oxygen is the third-most abundant element in the universe, after hydrogen, at standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. This is an important part of the atmosphere and diatomic oxygen gas constitutes 20. 8% of the Earths atmosphere, additionally, as oxides the element makes up almost half of the Earths crust. Most of the mass of living organisms is oxygen as a component of water, conversely, oxygen is continuously replenished by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide. Oxygen is too reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form of oxygen, ozone, strongly absorbs ultraviolet UVB radiation, but ozone is a pollutant near the surface where it is a by-product of smog. At low earth orbit altitudes, sufficient atomic oxygen is present to cause corrosion of spacecraft, the name oxygen was coined in 1777 by Antoine Lavoisier, whose experiments with oxygen helped to discredit the then-popular phlogiston theory of combustion and corrosion. One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle, Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries later Leonardo da Vinci built on Philos work by observing that a portion of air is consumed during combustion and respiration, Oxygen was discovered by the Polish alchemist Sendivogius, who considered it the philosophers stone. In the late 17th century, Robert Boyle proved that air is necessary for combustion, English chemist John Mayow refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus. From this he surmised that nitroaereus is consumed in both respiration and combustion, Mayow observed that antimony increased in weight when heated, and inferred that the nitroaereus must have combined with it. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract De respiratione. Robert Hooke, Ole Borch, Mikhail Lomonosov, and Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a chemical element. This may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, which was then the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher, one part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx. The fact that a substance like wood gains overall weight in burning was hidden by the buoyancy of the combustion products
6.
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
7.
Hexagonal crystal family
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In crystallography, the hexagonal crystal family is one of the 6 crystal families. In the hexagonal family, the crystal is described by a right rhombic prism unit cell with two equal axes, an included angle of 120° and a height perpendicular to the two base axes. There are 52 space groups associated with it, which are exactly those whose Bravais lattice is either hexagonal or rhombohedral, the hexagonal crystal family consists of two lattice systems, hexagonal and rhombohedral. Each lattice system consists of one Bravais lattice, hence, there are 3 lattice points per unit cell in total and the lattice is non-primitive. The Bravais lattices in the hexagonal crystal family can also be described by rhombohedral axes, the unit cell is a rhombohedron. This is a cell with parameters a = b = c, α = β = γ ≠ 90°. In practice, the description is more commonly used because it is easier to deal with a coordinate system with two 90° angles. However, the axes are often shown in textbooks because this cell reveals 3m symmetry of crystal lattice. However, such a description is rarely used, the hexagonal crystal family consists of two crystal systems, trigonal and hexagonal. A crystal system is a set of point groups in which the point groups themselves, the trigonal crystal system consists of the 5 point groups that have a single three-fold rotation axis. The crystal structures of alpha-quartz in the example are described by two of those 18 space groups associated with the hexagonal lattice system. The hexagonal crystal system consists of the seven point groups such that all their groups have the hexagonal lattice as underlying lattice. Graphite is an example of a crystal that crystallizes in the crystal system. Note that the atom in the center of the HCP unit cell in the hexagonal lattice system does not appear in the unit cell of the hexagonal lattice. It is part of the two atom motif associated with each point in the underlying lattice. The trigonal crystal system is the crystal system whose point groups have more than one lattice system associated with their space groups. The 5 point groups in this system are listed below, with their international number and notation, their space groups in name. The point groups in this system are listed below, followed by their representations in Hermann–Mauguin or international notation and Schoenflies notation
8.
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
9.
Crystal habit
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In mineralogy, crystal habit is the characteristic external shape of an individual crystal or crystal group. A single crystals habit is a description of its shape and its crystallographic forms. Recognizing the habit may help in identifying a mineral, when the faces are well-developed due to uncrowded growth a crystal is called euhedral, one with partially developed faces is subhedral, and one with undeveloped crystal faces is called anhedral. The long axis of a quartz crystal typically has a six-sided prismatic habit with parallel opposite faces. Aggregates can be formed of individual crystals with euhedral to anhedral grains, the arrangement of crystals within the aggregate can be characteristic of certain minerals. For example, minerals used for asbestos insulation often grow in a fibrous habit, the terms used by mineralogists to report crystal habits describe the typical appearance of an ideal mineral. Recognizing the habit can aid in identification as some habits are characteristic, most minerals, however, do not display ideal habits due to conditions during crystallization. Minerals belonging to the crystal system do not necessarily exhibit the same habit. Some habits of a mineral are unique to its variety and locality, For example, while most sapphires form elongate barrel-shaped crystals, ordinarily, the latter habit is seen only in ruby. Sapphire and ruby are both varieties of the mineral, corundum. Some minerals may replace other existing minerals while preserving the originals habit, a classic example is tigers eye quartz, crocidolite asbestos replaced by silica. While quartz typically forms prismatic crystals, in tigers eye the original fibrous habit of crocidolite is preserved, the names of crystal habits are derived from, Predominant crystal faces. Abnormal grain growth Grain growth Crystallization
10.
Crystal twinning
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Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals in a variety of specific configurations, a twin boundary or composition surface separates the two crystals. Crystallographers classify twinned crystals by a number of twin laws and these twin laws are specific to the crystal system. The type of twinning can be a tool in mineral identification. Twinning can often be a problem in X-ray crystallography, as a crystal does not produce a simple diffraction pattern. Simple twinned crystals may be contact twins or penetration twins, contact twins share a single composition surface often appearing as mirror images across the boundary. Plagioclase, quartz, gypsum, and spinel often exhibit contact twinning, merohedral twinning occurs when the lattices of the contact twins superimpose in three dimensions, such as by relative rotation of one twin from the other. In penetration twins the individual crystals have the appearance of passing through each other in a symmetrical manner, orthoclase, staurolite, pyrite, and fluorite often show penetration twinning. If several twin crystal parts are aligned by the same twin law they are referred to as multiple or repeated twins, if these multiple twins are aligned in parallel they are called polysynthetic twins. When the multiple twins are not parallel they are cyclic twins, albite, calcite, and pyrite often show polysynthetic twinning. Closely spaced polysynthetic twinning is often observed as striations or fine lines on the crystal face. Rutile, aragonite, cerussite, and chrysoberyl often exhibit cyclic twinning, 2-normal twin, -when the twin plane and compositional plane lies noramally. 3-complex twin, -combination of parallel twinning and normal twinning on one compositional plane, there are three modes of formation of twinned crystals. Growth twins are the result of an interruption or change in the lattice during formation or growth due to a possible deformation from a larger substituting ion, deformation or gliding twins are the result of stress on the crystal after the crystal has formed. If a FCC metal like aluminum experiences extreme stresses, it will experience twinning as seen in the case of explosions, deformation twinning is a common result of regional metamorphism. Crystals that grow adjacent to each other may be aligned to resemble twinning and this parallel growth simply reduces system energy and is not twinning. Twin boundaries occur when two crystals of the same type intergrow, so only a slight misorientation exists between them. It is a highly symmetrical interface, often with one crystal the mirror image of the other, also and this is also a much lower-energy interface than the grain boundaries that form when crystals of arbitrary orientation grow together
11.
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
12.
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
13.
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
14.
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
15.
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
16.
Transparency and translucency
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In the field of optics, transparency is the physical property of allowing light to pass through the material without being scattered. On a macroscopic scale, the photons can be said to follow Snells Law, in other words, a translucent medium allows the transport of light while a transparent medium not only allows the transport of light but allows for image formation. The opposite property of translucency is opacity, transparent materials appear clear, with the overall appearance of one color, or any combination leading up to a brilliant spectrum of every color. When light encounters a material, it can interact with it in different ways. These interactions depend on the wavelength of the light and the nature of the material, photons interact with an object by some combination of reflection, absorption and transmission. Some materials, such as glass and clean water, transmit much of the light that falls on them and reflect little of it. Many liquids and aqueous solutions are highly transparent, absence of structural defects and molecular structure of most liquids are mostly responsible for excellent optical transmission. Materials which do not transmit light are called opaque, many such substances have a chemical composition which includes what are referred to as absorption centers. Many substances are selective in their absorption of light frequencies. They absorb certain portions of the spectrum while reflecting others. The frequencies of the spectrum which are not absorbed are either reflected or transmitted for our physical observation and this is what gives rise to color. The attenuation of light of all frequencies and wavelengths is due to the mechanisms of absorption. Transparency can provide almost perfect camouflage for animals able to achieve it and this is easier in dimly-lit or turbid seawater than in good illumination. Many marine animals such as jellyfish are highly transparent, at the atomic or molecular level, physical absorption in the infrared portion of the spectrum depends on the frequencies of atomic or molecular vibrations or chemical bonds, and on selection rules. Nitrogen and oxygen are not greenhouse gases because there is no absorption because there is no molecular dipole moment. With regard to the scattering of light, the most critical factor is the scale of any or all of these structural features relative to the wavelength of the light being scattered. Primary material considerations include, Crystalline structure, whether or not the atoms or molecules exhibit the long-range order evidenced in crystalline solids, glassy structure, scattering centers include fluctuations in density or composition. Microstructure, scattering centers include internal surfaces such as boundaries, crystallographic defects
17.
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
18.
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
19.
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
20.
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
21.
Melting point
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The melting point of a solid is the temperature at which it changes state from solid to liquid at atmospheric pressure. At the melting point the solid and liquid phase exist in equilibrium, the melting point of a substance depends on pressure and is usually specified at standard pressure. When considered as the temperature of the change from liquid to solid. Because of the ability of some substances to supercool, the point is not considered as a characteristic property of a substance. For most substances, melting and freezing points are approximately equal, for example, the melting point and freezing point of mercury is 234.32 kelvins. However, certain substances possess differing solid-liquid transition temperatures, for example, agar melts at 85 °C and solidifies from 31 °C to 40 °C, such direction dependence is known as hysteresis. The melting point of ice at 1 atmosphere of pressure is close to 0 °C. In the presence of nucleating substances the freezing point of water is the same as the melting point, the chemical element with the highest melting point is tungsten, at 3687 K, this property makes tungsten excellent for use as filaments in light bulbs. Many laboratory techniques exist for the determination of melting points, a Kofler bench is a metal strip with a temperature gradient. Any substance can be placed on a section of the strip revealing its thermal behaviour at the temperature at that point, differential scanning calorimetry gives information on melting point together with its enthalpy of fusion. A basic melting point apparatus for the analysis of crystalline solids consists of an oil bath with a transparent window, the several grains of a solid are placed in a thin glass tube and partially immersed in the oil bath. The oil bath is heated and with the aid of the melting of the individual crystals at a certain temperature can be observed. In large/small devices, the sample is placed in a heating block, the measurement can also be made continuously with an operating process. For instance, oil refineries measure the point of diesel fuel online, meaning that the sample is taken from the process. This allows for more frequent measurements as the sample does not have to be manually collected, for refractory materials the extremely high melting point may be determined by heating the material in a black body furnace and measuring the black-body temperature with an optical pyrometer. For the highest melting materials, this may require extrapolation by several hundred degrees, the spectral radiance from an incandescent body is known to be a function of its temperature. An optical pyrometer matches the radiance of a body under study to the radiance of a source that has been previously calibrated as a function of temperature, in this way, the measurement of the absolute magnitude of the intensity of radiation is unnecessary. However, known temperatures must be used to determine the calibration of the pyrometer, for temperatures above the calibration range of the source, an extrapolation technique must be employed
22.
Solubility
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Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent. The solubility of a substance depends on the physical and chemical properties of the solute and solvent as well as on temperature, pressure. The solubility of a substance is a different property from the rate of solution. Most often, the solvent is a liquid, which can be a substance or a mixture. One may also speak of solid solution, but rarely of solution in a gas, the extent of solubility ranges widely, from infinitely soluble such as ethanol in water, to poorly soluble, such as silver chloride in water. The term insoluble is often applied to poorly or very poorly soluble compounds, a common threshold to describe something as insoluble is less than 0.1 g per 100 mL of solvent. Under certain conditions, the solubility can be exceeded to give a so-called supersaturated solution. Metastability of crystals can also lead to apparent differences in the amount of a chemical that dissolves depending on its form or particle size. A supersaturated solution generally crystallises when seed crystals are introduced and rapid equilibration occurs, phenylsalicylate is one such simple observable substance when fully melted and then cooled below its fusion point. Solubility is not to be confused with the ability to dissolve a substance, for example, zinc dissolves in hydrochloric acid as a result of a chemical reaction releasing hydrogen gas in a displacement reaction. The zinc ions are soluble in the acid, the smaller a particle is, the faster it dissolves although there are many factors to add to this generalization. Crucially solubility applies to all areas of chemistry, geochemistry, inorganic, physical, organic, in all cases it will depend on the physical conditions and the enthalpy and entropy directly relating to the solvents and solutes concerned. By far the most common solvent in chemistry is water which is a solvent for most ionic compounds as well as a range of organic substances. This is a factor in acidity/alkalinity and much environmental and geochemical work. According to the IUPAC definition, solubility is the composition of a saturated solution expressed as a proportion of a designated solute in a designated solvent. Solubility may be stated in units of concentration such as molarity, molality, mole fraction, mole ratio, mass per volume. Solubility occurs under dynamic equilibrium, which means that solubility results from the simultaneous and opposing processes of dissolution, the solubility equilibrium occurs when the two processes proceed at a constant rate. The term solubility is used in some fields where the solute is altered by solvolysis
23.
Piezoelectricity
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Piezoelectricity /piˌeɪzoʊˌilɛkˈtrɪsɪti/ is the electric charge that accumulates in certain solid materials in response to applied mechanical stress. The word piezoelectricity means electricity resulting from pressure and it is derived from the Greek piezō or piezein, which means to squeeze or press, and ēlektron, which means amber, an ancient source of electric charge. Piezoelectricity was discovered in 1880 by French physicists Jacques and Pierre Curie, the piezoelectric effect is understood as the linear electromechanical interaction between the mechanical and the electrical state in crystalline materials with no inversion symmetry. The piezoelectric effect is a process in that materials exhibiting the direct piezoelectric effect also exhibit the reverse piezoelectric effect. For example, lead zirconate titanate crystals will generate measurable piezoelectricity when their structure is deformed by about 0. 1% of the original dimension. Conversely, those same crystals will change about 0. 1% of their static dimension when an electric field is applied to the material. The inverse piezoelectric effect is used in the production of sound waves. The pyroelectric effect, by which a material generates a potential in response to a temperature change, was studied by Carl Linnaeus. Drawing on this knowledge, both René Just Haüy and Antoine César Becquerel posited a relationship between stress and electric charge, however, experiments by both proved inconclusive. The first demonstration of the piezoelectric effect was in 1880 by the brothers Pierre Curie. Quartz and Rochelle salt exhibited the most piezoelectricity, the Curies, however, did not predict the converse piezoelectric effect. The converse effect was mathematically deduced from fundamental principles by Gabriel Lippmann in 1881. For the next few decades, piezoelectricity remained something of a laboratory curiosity, more work was done to explore and define the crystal structures that exhibited piezoelectricity. The first practical application for piezoelectric devices was sonar, first developed during World War I, in France in 1917, Paul Langevin and his coworkers developed an ultrasonic submarine detector. The detector consisted of a transducer, made of quartz crystals carefully glued between two steel plates, and a hydrophone to detect the returned echo. The use of piezoelectricity in sonar, and the success of that project, over the next few decades, new piezoelectric materials and new applications for those materials were explored and developed. Piezoelectric devices found homes in many fields, ceramic phonograph cartridges simplified player design, were cheap and accurate, and made record players cheaper to maintain and easier to build. The development of the ultrasonic transducer allowed for easy measurement of viscosity and elasticity in fluids and solids, ultrasonic time-domain reflectometers could find flaws inside cast metal and stone objects, improving structural safety
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Violet (color)
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Violet is the color of amethyst, lavender and beautyberries. It takes its name from the violet flower, Violet is the color at the end of the visible spectrum of light between blue and the invisible ultraviolet. Violet color has a predominant light wavelength of roughly 380-450 nanometers, light with a shorter wavelength than violet but longer than X-rays and gamma rays is called ultraviolet. In the color wheel used by painters, it is located between blue and purple. This is not true violet, since it is composed of multiple longer wavelengths rather than a wavelength shorter than that of blue light. Violet and purple look very similar, but violet is a color, with its own set of wavelengths on the spectrum of visible light, while purple is a composite color, made by combining blue. In history, violet and purple have long associated with royalty and majesty. The emperors of Rome wore purple togas, as did the Byzantine emperors, during the Middle Ages violet was worn by bishops and university professors and was often used in art as the color of the robes of the Virgin Mary. According to surveys in Europe and the United States, violet is the people most often associate with extravagance and individualism, the unconventional, the artificial. In Chinese painting, the color represents the harmony of the universe because it is a combination of red. In Hinduism and Buddhism violet is associated with the Crown Chakra, from the Middle English and old French violette, and from the Latin viola, the names of the violet flower. The first recorded use of violet as a name in English was in 1370. Violet can also refer to the first violas which were painted a similar color. In the traditional color used by painters, violet and purple are both placed between red and blue. Purple occupies the space closer to red, between crimson and violet, Violet is closer to blue, and usually less intense and bright than purple. The range of purples is created by combining blue and red light of any intensities, Violet is one of the oldest colors used by man. It has also found in the cave of Altamira and Lascaux. It was sometimes used an alternative to black charcoal, sticks of manganese, used for drawing, have been found at sites occupied by Neanderthal man in France and Israel
25.
Quartz
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Quartz is the second most abundant mineral in Earths continental crust, behind feldspar. There are many different varieties of quartz, several of which are semi-precious gemstones, since antiquity, varieties of quartz have been the most commonly used minerals in the making of jewelry and hardstone carvings, especially in Eurasia. The word quartz is derived from the German word Quarz and its Middle High German ancestor twarc, the Ancient Greeks referred to quartz as κρύσταλλος derived from the Ancient Greek κρύος meaning icy cold, because some philosophers apparently believed the mineral to be a form of supercooled ice. Today, the rock crystal is sometimes used as an alternative name for the purest form of quartz. Quartz belongs to the crystal system. The ideal crystal shape is a six-sided prism terminating with six-sided pyramids at each end, well-formed crystals typically form in a bed that has unconstrained growth into a void, usually the crystals are attached at the other end to a matrix and only one termination pyramid is present. However, doubly terminated crystals do occur where they develop freely without attachment, a quartz geode is such a situation where the void is approximately spherical in shape, lined with a bed of crystals pointing inward. α-quartz crystallizes in the crystal system, space group P3121 and P3221 respectively. β-quartz belongs to the system, space group P6222 and P6422. These space groups are truly chiral, both α-quartz and β-quartz are examples of chiral crystal structures composed of achiral building blocks. The transformation between α- and β-quartz only involves a comparatively minor rotation of the tetrahedra with respect to one another, although many of the varietal names historically arose from the color of the mineral, current scientific naming schemes refer primarily to the microstructure of the mineral. Color is an identifier for the cryptocrystalline minerals, although it is a primary identifier for the macrocrystalline varieties. Pure quartz, traditionally called rock crystal or clear quartz, is colorless and transparent or translucent, common colored varieties include citrine, rose quartz, amethyst, smoky quartz, milky quartz, and others. The most important distinction between types of quartz is that of macrocrystalline and the microcrystalline or cryptocrystalline varieties, the cryptocrystalline varieties are either translucent or mostly opaque, while the transparent varieties tend to be macrocrystalline. Chalcedony is a form of silica consisting of fine intergrowths of both quartz, and its monoclinic polymorph moganite. Other opaque gemstone varieties of quartz, or mixed rocks including quartz, often including contrasting bands or patterns of color, are agate, carnelian or sard, onyx, heliotrope, amethyst is a form of quartz that ranges from a bright to dark or dull purple color. The worlds largest deposits of amethysts can be found in Brazil, Mexico, Uruguay, Russia, France, Namibia, sometimes amethyst and citrine are found growing in the same crystal. It is then referred to as ametrine, an amethyst is formed when there is iron in the area where it was formed
26.
Jewelry
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Jewellery or jewelry consists of small decorative items worn for personal adornment, such as brooches, rings, necklaces, earrings, and bracelets. Jewellery may be attached to the body or the clothes, for many centuries metal, often combined with gemstones, has been the normal material for jewellery, but other materials such as shells and other plant materials may be used. It is one of the oldest type of archaeological artefact – with 100, historically, the most widespread influence on jewellery in terms of design and style have come from Asia. Jewellery may be made from a range of materials. Gemstones and similar such as amber and coral, precious metals, beads, and shells have been widely used. In most cultures jewellery can be understood as a symbol, for its material properties, its patterns. Jewellery has been made to nearly every body part, from hairpins to toe rings. The word jewellery itself is derived from the jewel, which was anglicised from the Old French jouel. In British English, Indian English, New Zealand English, Hiberno-English, Australian English, both are used in Canadian English, though jewelry prevails by a two to one margin. Numerous cultures store wedding dowries in the form of jewellery or make jewellery as a means to store or display coins, alternatively, jewellery has been used as a currency or trade good, an example being the use of slave beads. Many items of jewellery, such as brooches and buckles, originated as functional items. Jewellery can also symbolise group membership or status, wearing of amulets and devotional medals to provide protection or ward off evil is common in some cultures. These may take the form of symbols, stones, plants, animals, body parts, in creating jewellery, gemstones, coins, or other precious items are often used, and they are typically set into precious metals. Alloys of nearly every metal known have been encountered in jewellery, bronze, for example, was common in Roman times. Modern fine jewellery usually includes gold, white gold, platinum, palladium, titanium, most contemporary gold jewellery is made of an alloy of gold, the purity of which is stated in karats, indicated by a number followed by the letter K. American gold jewellery must be of at least 10K purity, many whimsical fashions were introduced in the extravagant eighteenth century. Cameos that were used in connection with jewellery were the attractive trinkets along with many of the objects such as brooches, ear-rings. Some of the necklets were made of pieces joined with the gold chains were in and bracelets were also made sometimes to match the necklet
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Koine Greek
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It was based mainly on Attic and related Ionic speech forms, with various admixtures brought about through dialect levelling with other varieties. Koine Greek displayed a wide spectrum of different styles, ranging from more conservative literary forms to the vernaculars of the time. As the dominant language of the Byzantine Empire, it developed further into Medieval Greek, Koine Greek remained the court language of the Byzantine Empire until its dissolution in 1453, while Medieval and eventually Modern Greek were the everyday language. Literary Koine was the medium of much of post-classical Greek literary and scholarly writing, such as the works of Plutarch, Koine is also the language of the Christian New Testament, of the Septuagint, and of most early Christian theological writing by the Church Fathers. In this context, Koine Greek is also known as Biblical, New Testament and it continues to be used as the liturgical language of services in the Greek Orthodox Church. The word koinē is the Greek word for common, and is understood as referring to the common dialect. The word is pronounced /kɔɪˈneɪ/, /ˈkɔɪneɪ/ or /kiːˈniː/ in US English, the pronunciation of the word in Koine gradually changed from Greek pronunciation, to Greek pronunciation. Its pronunciation in Modern Greek is, the term was applied in several different senses by ancient scholars. Others chose to refer to Koine as the Alexandrian dialect or the dialect of Alexandria, the former was often used by modern classicists. Koine Greek arose as a dialect within the armies of Alexander the Great. Under the leadership of Macedon, their newly formed common variety was spoken from the Ptolemaic Kingdom of Egypt to the Seleucid Empire of Mesopotamia and it replaced existing ancient Greek dialects with an everyday form that people anywhere could understand. The passage into the period, known as Medieval Greek. The post-Classical period of Greek thus refers to the creation and evolution of Koine Greek throughout the entire Hellenistic, the linguistic roots of the Common Greek dialect had been unclear since ancient times. During the Hellenistic period, most scholars thought of Koine as the result of the mixture of the four main Ancient Greek dialects, ἡ ἐκ τῶν τεττάρων συνεστῶσα. The view accepted by most scholars today was given by the Greek linguist Georgios Hatzidakis, who showed that, despite the composition of the Four, the stable nucleus of Koine Greek is Attic. In other words, Koine Greek can be regarded as Attic with the admixture of elements especially from Ionic, the degree of importance of the non-Attic linguistic elements on Koine can vary depending on the region of the Hellenistic World. The literary Koine of the Hellenistic age resembles Attic in such a degree that it is mentioned as Common Attic. Koine Greek was therefore considered a form of Greek which was not worthy of attention
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Ancient Greece
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Ancient Greece was a civilization belonging to a period of Greek history from the Greek Dark Ages of the 12th-9th centuries BC to the end of antiquity. Immediately following this period was the beginning of the Early Middle Ages and this was followed by the period of Classical Greece, an era that began with the Greco-Persian Wars, lasting from the 5th to 4th centuries BC. Due to the conquests by Alexander the Great of Macedonia, Hellenistic civilization flourished from Central Asia to the end of the Mediterranean Sea. Classical Greek culture, especially philosophy, had a influence on ancient Rome. For this reason Classical Greece is generally considered to be the culture which provided the foundation of modern Western culture and is considered the cradle of Western civilization. Classical Antiquity in the Mediterranean region is considered to have begun in the 8th century BC. Classical Antiquity in Greece is preceded by the Greek Dark Ages and this period is succeeded, around the 8th century BC, by the Orientalizing Period during which a strong influence of Syro-Hittite, Jewish, Assyrian, Phoenician and Egyptian cultures becomes apparent. The end of the Dark Ages is also dated to 776 BC. The Archaic period gives way to the Classical period around 500 BC, Ancient Periods Astronomical year numbering Dates are approximate, consult particular article for details The history of Greece during Classical Antiquity may be subdivided into five major periods. The earliest of these is the Archaic period, in which artists made larger free-standing sculptures in stiff, the Archaic period is often taken to end with the overthrow of the last tyrant of Athens and the start of Athenian Democracy in 508 BC. It was followed by the Classical period, characterized by a style which was considered by observers to be exemplary, i. e. classical, as shown in the Parthenon. This period saw the Greco-Persian Wars and the Rise of Macedon, following the Classical period was the Hellenistic period, during which Greek culture and power expanded into the Near and Middle East. This period begins with the death of Alexander and ends with the Roman conquest, Herodotus is widely known as the father of history, his Histories are eponymous of the entire field. Herodotus was succeeded by authors such as Thucydides, Xenophon, Demosthenes, Plato, most of these authors were either Athenian or pro-Athenian, which is why far more is known about the history and politics of Athens than those of many other cities. Their scope is limited by a focus on political, military and diplomatic history, ignoring economic. In the 8th century BC, Greece began to emerge from the Dark Ages which followed the fall of the Mycenaean civilization, literacy had been lost and Mycenaean script forgotten, but the Greeks adopted the Phoenician alphabet, modifying it to create the Greek alphabet. The Lelantine War is the earliest documented war of the ancient Greek period and it was fought between the important poleis of Chalcis and Eretria over the fertile Lelantine plain of Euboea. Both cities seem to have suffered a decline as result of the long war, a mercantile class arose in the first half of the 7th century BC, shown by the introduction of coinage in about 680 BC
29.
Drinking
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Drinking is the act of ingesting water or other liquids into the body through the mouth. Water is required for many of life’s physiological processes, both excessive and inadequate water intake are associated with health problems. When a liquid is poured into a human mouth, the swallowing process is completed by peristalsis which delivers the liquid to the stomach, much of the activity is abetted by gravity. The liquid may be poured from the hands or drinkware may be used as vessels, drinking can also be performed by acts of inhalation, typically when imbibing hot liquids or drinking from a spoon. Infants employ a method of suction wherein the lips are pressed tight around a source, as in breastfeeding, amphibians and aquatic animals which live in freshwater do not need to drink, they absorb water steadily through the skin by osmosis. Saltwater fish, however, drink through the mouth as they swim, by necessity, terrestrial animals in captivity become accustomed to drinking water, but most free-roaming animals stay hydrated through the fluids and moisture in fresh food. When conditions impel them to drink from bodies of water, the methods, many desert animals do not drink even if water becomes available, but rely on eating succulent plants. Cats, canines, and ruminants all lower the neck and lap in water with their powerful tongues, cats and canines lap up water with the tongue in a spoon-like shape. Ruminants and most other herbivores partially submerge the tip of the mouth in order to draw in water by means of an action with the tongue held straight. Cats drink at a slower pace than ruminants, who face greater natural predation hazards. Uniquely, elephants draw water into their trunks and squirt it into their mouths, most birds scoop or draw water into the buccal areas of their bills, raising and tilting their heads back to drink. An exception is the common pigeon which can suck in water directly by inhalation, like nearly all other life forms, humans require water for tissue hydration. Lack of hydration causes thirst, a desire to drink which is regulated by the hypothalamus in response to changes in the bodys electrolyte levels. A decline in body water is called dehydration and will eventually lead to death by hypernatremia. Methods used in the management of dehydration include assisted drinking or oral rehydration therapy, an overconsumption of water can lead to water intoxication, which can dangerously dilute the concentration of salts in the body. Overhydration sometimes occurs among athletes and outdoor laborers, but it can also be a sign of disease or damage to the hypothalamus, a persistent desire to drink inordinate quantities of water is a psychological condition termed polydipsia. It is often accompanied by polyuria and may itself be a symptom of Diabetes mellitus or Diabetes insipidus, a daily intake of water is required for the normal physiological functioning of the human body. The USDA recommends an intake of total water, not necessarily by drinking but by consumption of water contained in other beverages
30.
Transition metal
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Many scientists describe a transition metal as any element in the d-block of the periodic table, which includes groups 3 to 12 on the periodic table. In actual practice, the lanthanide and actinide series are also considered transition metals and are called inner transition metals. Cotton and Wilkinson expand the brief IUPAC definition by specifying which elements are included, as well as the elements of groups 4 to 11, they add scandium and yttrium in group 3 which have a partially filled d subshell in the metallic state. These last two elements are included even though they do not seem to possess the properties which are so characteristic of the transition metals in general. Lanthanum and actinium in Group 3 are however classified as lanthanides and actinides respectively and these elements are now known as the d-block. In the d-block the atoms of the elements have between 1 and 10 d electrons, Sc and Y in Group 3 are also generally recognized as transition metals. However the elements La–Lu and Ac–Lr and Group 12 attract different definitions from different authors, many chemistry textbooks and printed periodic tables classify La and Ac as Group 3 elements and transition metals, since their atomic ground-state configurations are s2d1 like Sc and Y. The elements Ce-Lu are considered as the series and Th-Lr as the actinide series. The two series together are classified as elements, or as inner transition elements. Some inorganic chemistry textbooks include La with the lanthanides and Ac with the actinides, a third classification defines the f-block elements as La-Yb and Ac-No, while placing Lu and Lr in Group 3. This is based on the Aufbau principle for filling electron subshells, in which 4f is filled before 5d, zinc, cadmium, and mercury are generally excluded from the transition metals as they have the electronic configuration d10s2, with no incomplete d shell. In the oxidation state +2 the ions have the electronic configuration d10, however, these elements can exist in other oxidation states, including the +1 oxidation state, as in the diatomic ion Hg2+2. The group 12 elements Zn, Cd and Hg may therefore, under certain rules, however, it is often convenient to include these elements in a discussion of the transition elements. Another example occurs in the Irving-Williams series of stability constants of complexes, although meitnerium, darmstadtium, and roentgenium are within the d-block and are expected to behave as transition metals, this has not yet been experimentally confirmed. The general electronic configuration of the elements is d1, 10n s1,2. The period 6 and 7 transition metals also add f1,14 electrons and this rule is however only approximate – it only holds for some of the transition elements, and only then in their neutral ground state. The d-sub-shell is the next-to-last sub-shell and is denoted as d -sub-shell, the number of s electrons in the outermost s sub-shell is generally one or two except palladium, with no electron in that s-sub shell in its ground state. The s-sub-shell in the shell is represented as the ns sub-shell
31.
Siberia
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Siberia is an extensive geographical region, and by the broadest definition is also known as North Asia. Siberia has historically been a part of Russia since the 17th century, the territory of Siberia extends eastwards from the Ural Mountains to the watershed between the Pacific and Arctic drainage basins. It stretches southwards from the Arctic Ocean to the hills of north-central Kazakhstan and to the borders of Mongolia. With an area of 13.1 million square kilometres, Siberia accounts for 77% of Russias land area and this is equivalent to an average population density of about 3 inhabitants per square kilometre, making Siberia one of the most sparsely populated regions on Earth. If it were a country by itself, it would still be the largest country in area, the origin of the name is unknown. Some sources say that Siberia originates from the Siberian Tatar word for sleeping land, another account sees the name as the ancient tribal ethnonym of the Sirtya, a folk, which spoke a language that later evolved into the Ugric languages. This ethnic group was assimilated to the Siberian Tatar people. The modern usage of the name was recorded in the Russian language after the Empires conquest of the Siberian Khanate, a further variant claims that the region was named after the Xibe people. The Polish historian Chycliczkowski has proposed that the name derives from the word for north. He said that the neighbouring Chinese, Arabs and Mongolians would not have known Russian and he suggests that the name is a combination of two words, su and bir. The region is of significance, as it contains bodies of prehistoric animals from the Pleistocene Epoch. Specimens of Goldfuss cave lion cubs, Yuka and another woolly mammoth from Oymyakon, a rhinoceros from the Kolyma River. The Siberian Traps were formed by one of the largest known volcanic events of the last 500 million years of Earths geological history. They continued for a million years and are considered a cause of the Great Dying about 250 million years ago. At least three species of human lived in Southern Siberia around 40,000 years ago, H. sapiens, H. neanderthalensis, the last was determined in 2010, by DNA evidence, to be a new species. Siberia was inhabited by different groups of such as the Enets, the Nenets, the Huns, the Scythians. The Khan of Sibir in the vicinity of modern Tobolsk was known as a prominent figure who endorsed Kubrat as Khagan of Old Great Bulgaria in 630, the Mongols conquered a large part of this area early in the 13th century. With the breakup of the Golden Horde, the autonomous Khanate of Sibir was established in the late 15th century, turkic-speaking Yakut migrated north from the Lake Baikal region under pressure from the Mongol tribes during the 13th to 15th century
32.
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
33.
Brazil
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Brazil, officially the Federative Republic of Brazil, is the largest country in both South America and Latin America. As the worlds fifth-largest country by area and population, it is the largest country to have Portuguese as an official language. Its Amazon River basin includes a vast tropical forest, home to wildlife, a variety of ecological systems. This unique environmental heritage makes Brazil one of 17 megadiverse countries, Brazil was inhabited by numerous tribal nations prior to the landing in 1500 of explorer Pedro Álvares Cabral, who claimed the area for the Portuguese Empire. Brazil remained a Portuguese colony until 1808, when the capital of the empire was transferred from Lisbon to Rio de Janeiro, in 1815, the colony was elevated to the rank of kingdom upon the formation of the United Kingdom of Portugal, Brazil and the Algarves. Independence was achieved in 1822 with the creation of the Empire of Brazil, a state governed under a constitutional monarchy. The ratification of the first constitution in 1824 led to the formation of a bicameral legislature, the country became a presidential republic in 1889 following a military coup détat. An authoritarian military junta came to power in 1964 and ruled until 1985, Brazils current constitution, formulated in 1988, defines it as a democratic federal republic. The federation is composed of the union of the Federal District, the 26 states, Brazils economy is the worlds ninth-largest by nominal GDP and seventh-largest by GDP as of 2015. A member of the BRICS group, Brazil until 2010 had one of the worlds fastest growing economies, with its economic reforms giving the country new international recognition. Brazils national development bank plays an important role for the economic growth. Brazil is a member of the United Nations, the G20, BRICS, Unasul, Mercosul, Organization of American States, Organization of Ibero-American States, CPLP. Brazil is a power in Latin America and a middle power in international affairs. One of the worlds major breadbaskets, Brazil has been the largest producer of coffee for the last 150 years and it is likely that the word Brazil comes from the Portuguese word for brazilwood, a tree that once grew plentifully along the Brazilian coast. In Portuguese, brazilwood is called pau-brasil, with the word brasil commonly given the etymology red like an ember, formed from Latin brasa and the suffix -il. As brazilwood produces a red dye, it was highly valued by the European cloth industry and was the earliest commercially exploited product from Brazil. The popular appellation eclipsed and eventually supplanted the official Portuguese name, early sailors sometimes also called it the Land of Parrots. In the Guarani language, a language of Paraguay, Brazil is called Pindorama
34.
Prasiolite
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Prasiolite is a green variety of quartz, a silicate mineral chemically silicon dioxide. Since 1950, almost all natural prasiolite has come from a small Brazilian mine, naturally occurring prasiolite is also found in the Thunder Bay area of Canada. Most prasiolite sold is used in jewellery settings, where it can substitute for far more expensive precious gemstones and it is a rare stone in nature, artificially produced prasiolite is heat treated amethyst. Most amethyst will turn yellow or orange when heated producing citrine, but some amethyst will turn green when treated. Currently, almost all prasiolite on the results from a combination of heat treatment. Green quartz is sometimes called green amethyst, which is not an acceptable name for the material. It is actually against Federal Trade Commission Guidelines to call prasiolite green amethyst, other names for green quartz are vermarine, greened amethyst, or lime citrine. The word prasiolite literally means scallion green-colored stone and is derived from Greek πράσον prason meaning leek, the mineral was given its name due to its green-colored appearance. Natural prasiolite is a light, translucent green. Darker green quartz is generally the result of artificial treatment, list of minerals - Prasiolite on Mindat. org
35.
Emerald
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Emerald is a gemstone and a variety of the mineral beryl colored green by trace amounts of chromium and sometimes vanadium. Beryl has a hardness of 7. 5–8 on the Mohs scale, most emeralds are highly included, so their toughness is classified as generally poor. The word emerald is derived, from Vulgar Latin, esmaralda/esmaraldus, a variant of Latin smaragdus, emeralds, like all colored gemstones, are graded using four basic parameters–the four Cs of Connoisseurship, Color, Clarity, Cut and Carat weight. Before the 20th century, jewelers used the water, as in a gem of the finest water. Normally, in the grading of colored gemstones, color is by far the most important criterion, however, in the grading of emeralds, clarity is considered a close second. A fine emerald must possess not only a pure verdant green hue as described below, in the 1960s, the American jewelry industry changed the definition of emerald to include the green vanadium-bearing beryl as emerald. As a result, vanadium emeralds purchased as emeralds in the United States are not recognized as such in the UK, in America, the distinction between traditional emeralds and the new vanadium kind is often reflected in the use of terms such as Colombian Emerald. In gemology, color is divided into three components, hue, saturation, and tone, emeralds occur in hues ranging from yellow-green to blue-green, with the primary hue necessarily being green. Yellow and blue are the normal secondary hues found in emeralds, only gems that are medium to dark in tone are considered emerald, light-toned gems are known instead by the species name green beryl. The finest emerald are approximately 75% tone on a scale where 0% tone would be colorless, in addition, a fine emerald should be well saturated and have a hue that is bright. Gray is the normal saturation modifier or mask found in emerald, Emerald tends to have numerous inclusions and surface breaking fissures. Unlike diamond, where the standard, i. e. 10× magnification, is used to grade clarity. Thus, if an emerald has no visible inclusions to the eye it is considered flawless, stones that lack surface breaking fissures are extremely rare and therefore almost all emeralds are treated to enhance the apparent clarity. The inclusions and fissures within an emerald are sometime described as jardin, imperfections are unique for each emerald and can be used to identify a particular stone. Eye-clean stones of a vivid primary green hue, with no more than 15% of any hue or combination of a medium-dark tone. The relative non-uniformity motivates the cutting of emeralds in cabochon form, faceted emeralds are most commonly given an oval cut, or the signature emerald cut, a rectangular cut with facets around the top edge. Most emeralds are oiled as part of the process, in order to fill in surface-reaching cracks so that clarity and stability are improved. Cedar oil, having a refractive index, is often used in this widely adopted practice
36.
Lapidary
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A lapidary is an artist or artisan who forms stone, minerals, or gemstones into decorative items such as cabochons, engraved gems, including cameos, and faceted designs. The primary techniques employed are cutting, grinding, and polishing, carving is an important, but specialised technique. Hardstone carving is the used in art history for objects produced by the specialised carving techniques. Diamond cutters are not referred to as lapidaries, due to the specialized techniques which are required to work diamond. By extension the term lapidary has sometimes applied to collectors of and dealer in gems. The etymological roots of lapidary is in the Latin word lapis which means stone, the term evolved from lapidarius meaning stonecutter or working with stone, into Old French lapidaire, thereon to mean one skilled in working with precious stones in 14th century. These powers included the belief in the ability of stones to prevent harm, the word appeared as an English adjective in the 18th century. The earliest known lapidary work likely occurred during the Stone Age, as people created tools from stone, they inevitably realized that some geological materials were harder than others. The next earliest documented examples of one may consider to be lapidary arts came in the form of drilling stone. The earliest roots of drilling rocks, a method, date back to approximately one million years ago. The early Egyptians developed cutting and jewelry fashioning methods for lapis lazuli, turquoise, the lapidary arts were quite well developed in the Indian subcontinent by early 1st millennium CE. They discuss sources of gems and diamonds, their origins, qualities, several other Sanskrit texts on gems and lapidary, have been dated to post-10th century suggesting a continuous lapidary practice. According to Jason Hawkes and Stephanie Wynne-Jones, archaeological evidence suggests that trade between Africa and India, in products from lapidary arts, was established in the 1st millennium CE, lapidary has been a significant tradition in early Mesoamerica. These were made from shell, jade, turquoise and greenstones, the lapidary products were used as a status symbol, offerings and during burials. The Aztec used string saw, reed and bone drills for their lapidary arts, apart from figurative carving, there are three broad categories of lapidary arts. These are the procedures of tumbling, cabochon cutting, and faceting, most modern lapidary work is done using motorized equipment. Polishing is done with resin or metal bonded emery, silicon carbide, in older systems the grinding and polishing powders were applied separately to the grinding or buffing wheel. Often, the final polish will use a different medium, such as tin oxide or cerium oxide, cutting of harder stones is done with a diamond tipped saw
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Dichroism
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The original meaning of dichroic, from the Greek dikhroos, two-coloured, refers to any optical device which can split a beam of light into two beams with differing wavelengths. This kind of dichroic device does not usually depend on the polarization of the light, the term dichromatic is also used in this sense. When the polarization states in question are right and left-handed circular polarization and this is more generally referred to as pleochroism, and the technique can be used in mineralogy to identify minerals. In some materials, such as herapathite or Polaroid sheets, the effect is not strongly dependent on wavelength. Dichroism, in the second meaning above, occurs in liquid crystals due to either the optical anisotropy of the structure or the presence of impurities or the presence of dichroic dyes. The latter is called a guest–host effect
38.
Ametrine
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Ametrine, also known as trystine or by its trade name as bolivianite, is a naturally occurring variety of quartz. It is a mixture of amethyst and citrine with zones of purple, almost all commercially available ametrine is mined only in Bolivia. The colour of the zones visible within ametrine are due to differing oxidation states of iron within the crystal, the different oxidation states occur due to there being a temperature gradient across the crystal during its formation. Artificial ametrine can be created by differential heat treatment of amethyst, most ametrine in the low price segment can be assumed to stem from synthetic material. Since 1994, a Russian laboratory has perfected the production of bicolored quartz crystals that are later irradiated to bring out the typical ametrine colors. Green-yellow or golden-blue ametrine does not exist naturally, archived September 5,2006, at the Wayback Machine
39.
Intaglio (printmaking)
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Intaglio is the family of printing and printmaking techniques in which the image is incised into a surface and the incised line or sunken area holds the ink. It is the direct opposite of a relief print, normally, copper or zinc plates are used as a surface or matrix, and the incisions are created by etching, engraving, drypoint, aquatint or mezzotint. Collagraphs may also be printed as intaglio plates, in etching, for example, the plate is covered in a resin ground or an acid-resistant wax material. Using an etching needle, or a tool, the image is engraved into the ground. The plate is dipped into acid. The acid bites into the surface of the plate where it was exposed, biting is a printmaking term to describe the acids etching, or incising, of the image. After the plate is bitten, the plate is removed from the acid bath. To print an intaglio plate, ink is applied to the surface by wiping and/or dabbing the plate to push the ink into the recessed lines, the plate is then rubbed with tarlatan cloth to remove most of the excess ink. The final smooth wipe is often done with newspaper or old public phone book pages, a damp piece of paper is placed on top of the plate, so that when going through the press the damp paper will be able to be squeezed into the plates ink-filled grooves. The paper and plate are covered by a thick blanket to ensure even pressure when going through the rolling press. The rolling press applies very high pressure through the blanket to push the paper into the grooves on the plate, the blanket is then lifted, revealing the paper and printed image. Martin Schongauer was one of the earliest known artists to exploit the copper-engraving technique, italian and Netherlandish engraving began slightly after the Germans, but were well developed by 1500. Drypoint and etching were also German inventions of the century, probably by the Housebook Master. In the nineteenth century, Viennese printer Karel Klíč introduced a combined intaglio, photogravure retained the smooth continuous tones of photography but was printed using a chemically-etched copper plate. This permitted a photographic image to be printed on regular paper, at one time intaglio printing was used for all mass-printed materials including banknotes, stock certificates, newspapers and magazines, fabrics, wallpapers and sheet music. Today intaglio engraving is largely used for paper or plastic currency, banknotes, passports, photogravure, an intaglio photo-printmaking process Rotogravure Line engraving Viscosity printing History of printing Intaglio and other printmaking definitions
40.
Engraved gem
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An engraved gem is a small gemstone, usually semi-precious, that has been carved, in the Western tradition normally with images or inscriptions only on one face. The engraving of gemstones was a luxury art form in the ancient world. Strictly speaking, engraving means carving in intaglio, but relief carvings are covered by the term. This article uses cameo in its sense, to denote a carving exploiting layers of differently coloured stone. The activity is also called gem carving, and the artists gem-cutters, vessels like the Cup of the Ptolemies and heads or figures carved in the round are also known as hardstone carvings and similar terms. Glyptics, or glyptic art, covers the field of small carved stones, including seals and inscriptions. A finely carved seal was practical, as it made more difficult – the distinctive personal signature did not really exist in antiquity. Gems were mostly cut by using abrasive powder from harder stones in conjunction with a hand-drill, emery has been mined for abrasive powder on Naxos since antiquity. Some early types of seal were cut by hand, rather than a drill, there is no evidence that magnifying lenses were used by gem cutters in antiquity. A medieval guide to gem-carving techniques survives from Theophilus Presbyter, byzantine cutters used a flat-edged wheel on a drill for intaglio work, while Carolingian ones used round-tipped drills, it is unclear where they learnt this technique from. In intaglio gems at least, the cut surface is usually very well preserved. The colour of several gemstones can be enhanced by a number of methods, using heat, sugar. Many of these can be shown to have used since antiquity – since the 7th millennium BC in the case of heating. The technique has an ancient tradition in the Near East, and is represented in all or most early cultures from the area, and these were made in various types of stone, not all hardstone. The Greek tradition emerged in Ancient Greek art under Minoan influence on mainland Helladic culture, pre-Hellenic Ancient Egyptian seals tend to have inscriptions in hieroglyphs rather than images. The Biblical Book of Exodus describes the form of the hoshen, round or oval Greek gems are found from the 8th and 7th centuries BC, usually with animals in energetic geometric poses, often with a border marked by dots or a rim. Early examples are mostly in softer stones, Gems of the 6th century are more often oval, with a scarab back, and human or divine figures as well as animals, the scarab form was apparently adopted from Phoenicia. The forms are sophisticated for the period, despite the small size of the gems
41.
Caracalla
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Caracalla, formally Marcus Aurelius Severus Antoninus Augustus, was Roman emperor from AD198 to 217. A member of the Severan Dynasty, he was the eldest son of Septimius Severus, Caracalla reigned jointly with his father from 198 until Severus death in 211. Caracalla then ruled jointly with his younger brother Geta, with whom he had a fraught relationship, Caracallas reign was marked by domestic instability and external invasions from the Germanic people. Caracallas reign was notable for the Antonine Constitution, also known as the Edict of Caracalla, the edict gave all the enfranchised men Caracallas adopted praenomen and nomen, Marcus Aurelius. Towards the end of his rule, Caracalla began a campaign against the Parthian Empire and he did not see this campaign through to completion due to his assassination by a disaffected soldier in 217. He was succeeded as emperor by Macrinus after three days, Caracalla is presented in ancient sources as a tyrant and cruel leader, an image that has survived into modernity. Dio Cassius and Herodian present Caracalla as a soldier first and emperor second, in the 12th century, Geoffrey of Monmouth started the legend of Caracallas role as the king of Britain. Later, in the 18th century, Caracallas memory was revived in the works of French artists due to the parallels between Caracallas apparent tyranny and that of King Louis XVI, Modern works continue to portray Caracalla as a psychopathic and evil ruler. His rule is remembered as being one of the most tyrannical of all Roman emperors, Caracalla was born Lucius Septimius Bassianus. He was renamed Marcus Aurelius Antoninus at the age of seven as part of his fathers attempt at union with the families of Antoninus Pius and Marcus Aurelius. According to Aurelius Victor in his Epitome de Caesaribus, he became known by the agnomen Caracalla after a Gallic hooded tunic that he habitually wore and he may have begun wearing it during his campaigns on the Rhine and Danube. Dio generally referred to him as Tarautas, after a famously diminutive, Caracalla was born in Lugdunum, Gaul, on 4 April 188 to Septimius Severus and Julia Domna. He had a younger brother, Geta, who would briefly rule as co-emperor alongside him. Caracallas father, Septimius Severus, appointed Caracalla joint Augustus and full emperor from the year 198 onwards and his brother Geta was granted the same title in 210. In 202 Caracalla was forced to marry the daughter of Gaius Fulvius Plautianus, Fulvia Plautilla, by 205 Caracalla had succeeded in having Plautianus executed for treason, though he had probably fabricated the evidence of the plot himself. It was then that he banished his wife, whose later killing might have carried out under Caracallas orders. Caracallas father, Septimius Severus, died on 4 February 211 at Eboracum while on campaign in Caledonia, Caracalla and his brother, Publius Septimius Antoninus Geta, jointly inherited the throne upon their fathers death. Caracalla and Geta ended the campaign in Caledonia after concluding a peace with the Caledonians that returned the border of Roman Britain to the line demarcated by Hadrians Wall
42.
Sainte-Chapelle
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Begun some time after 1238 and consecrated on 26 April 1248, the Sainte-Chapelle is considered among the highest achievements of the Rayonnant period of Gothic architecture. It was commissioned by King Louis IX of France to house his collection of Passion relics, along with the Conciergerie, the Sainte-Chapelle is one of the earliest surviving buildings of the Capetian royal palace on the Île de la Cité. Although damaged during the French Revolution, and restored in the 19th century, the relics arrived in Paris in August 1239, carried from Venice by two Dominican friars. For the final stage of their journey they were carried by the King himself, barefoot and dressed as a penitent, the relics were stored in a large and elaborate silver chest, the Grand-Chasse, on which Louis spent a further 100,000 livres. The entire chapel, by contrast, cost 40,000 livres to build, until it was completed in 1248, the relics were housed at chapels at the Château de Vincennes and a specially built chapel at the Château de Saint-Germain-en-Laye. In 1246, fragments of the True Cross and the Holy Lance were added to Louis collection, the chapel was consecrated on 26 April 1248 and Louis relics were moved to their new home with great ceremony. As well as serving as a place of worship, the Sainte-Chapelle played an important role in the political and cultural ambitions of King Louis and his successors. Just as the Emperor could pass privately from his palace into the Hagia Sophia in Constantinople, the royal chapel is a prime example of the phase of Gothic architectural style called Rayonnant, marked by its sense of weightlessness and strong vertical emphasis. It stands squarely upon a lower chapel, which served as church for all the inhabitants of the palace. The king was recognized as a saint by the Catholic Church. The internal division into upper and lower chapels is clearly marked on the outside by a string-course, despite its decoration, the exterior is relatively simple and austere, devoid of flying buttresses or major sculpture and giving little hint of the richness within. No designer-builder is named in the archives concerned with the construction, modern scholarship rejects this attribution in favour of Jean de Chelles or Thomas de Cormont, while Robert Branner saw in the design the hand of an unidentified master mason from Amiens. As has often been argued however the influence on its overall design seems to have come from contemporary metalwork. The Parisian palatine chapel, built to house a reliquary, was itself like a precious reliquary turned inside out, although the interior is dominated by the stained glass, every inch of the remaining wall surface and the vault was also richly coloured and decorated. Above the dado level, mounted on the shafts that separate the great windows, are 12 larger-than-life-sized sculpted stone figures representing the 12 Apostles. Each carries a disk marked with the crosses that were traditionally marked on the pillars of a church at its consecration. Niches on the north and south sides of the chapel are the private oratories of the king and of his mother, fifteen huge mid-13th-century windows fill the nave and apse, while a large rose window with Flamboyant tracery dominates the western wall. Despite some damage the windows display a clear iconographical programme, the three windows of the eastern apse illustrate the New Testament, featuring scenes of The Passion with the Infancy of Christ and the Life of John the Evangelist
43.
Gemstone
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A gemstone is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks or organic materials that are not minerals are used for jewelry and are therefore often considered to be gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry because of their luster or other properties that have aesthetic value. Rarity is another characteristic that lends value to a gemstone, apart from jewelry, from earliest antiquity engraved gems and hardstone carvings, such as cups, were major luxury art forms. A gem maker is called a lapidary or gemcutter, a worker is a diamantaire. The carvings of Carl Fabergé are significant works in this tradition, the traditional classification in the West, which goes back to the ancient Greeks, begins with a distinction between precious and semi-precious, similar distinctions are made in other cultures. In modern usage the precious stones are diamond, ruby, sapphire, other stones are classified by their color, translucency and hardness. Another unscientific term for semi-precious gemstones used in art history and archaeology is hardstone, in modern times gemstones are identified by gemologists, who describe gems and their characteristics using technical terminology specific to the field of gemology. The first characteristic a gemologist uses to identify a gemstone is its chemical composition, for example, diamonds are made of carbon and rubies of aluminium oxide. Next, many gems are crystals which are classified by their crystal system such as cubic or trigonal or monoclinic, another term used is habit, the form the gem is usually found in. For example, diamonds, which have a crystal system, are often found as octahedrons. Gemstones are classified into different groups, species, and varieties, for example, ruby is the red variety of the species corundum, while any other color of corundum is considered sapphire. Other examples are the Emerald, aquamarine, red beryl, goshenite, heliodor, and morganite, gems are characterized in terms of refractive index, dispersion, specific gravity, hardness, cleavage, fracture, and luster. They may exhibit pleochroism or double refraction and they may have luminescence and a distinctive absorption spectrum. Material or flaws within a stone may be present as inclusions, gemstones may also be classified in terms of their water. This is a grading of the gems luster, transparency. Very transparent gems are considered first water, while second or third water gems are those of a lesser transparency, there is no universally accepted grading system for gemstones. Diamonds are graded using a system developed by the Gemological Institute of America in the early 1950s, historically, all gemstones were graded using the naked eye
44.
Egypt
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Egypt, officially the Arab Republic of Egypt, is a transcontinental country spanning the northeast corner of Africa and southwest corner of Asia by a land bridge formed by the Sinai Peninsula. Egypt is a Mediterranean country bordered by the Gaza Strip and Israel to the northeast, the Gulf of Aqaba to the east, the Red Sea to the east and south, Sudan to the south, and Libya to the west. Across the Gulf of Aqaba lies Jordan, and across from the Sinai Peninsula lies Saudi Arabia, although Jordan and it is the worlds only contiguous Afrasian nation. Egypt has among the longest histories of any country, emerging as one of the worlds first nation states in the tenth millennium BC. Considered a cradle of civilisation, Ancient Egypt experienced some of the earliest developments of writing, agriculture, urbanisation, organised religion and central government. One of the earliest centres of Christianity, Egypt was Islamised in the century and remains a predominantly Muslim country. With over 92 million inhabitants, Egypt is the most populous country in North Africa and the Arab world, the third-most populous in Africa, and the fifteenth-most populous in the world. The great majority of its people live near the banks of the Nile River, an area of about 40,000 square kilometres, the large regions of the Sahara desert, which constitute most of Egypts territory, are sparsely inhabited. About half of Egypts residents live in areas, with most spread across the densely populated centres of greater Cairo, Alexandria. Modern Egypt is considered to be a regional and middle power, with significant cultural, political, and military influence in North Africa, the Middle East and the Muslim world. Egypts economy is one of the largest and most diversified in the Middle East, Egypt is a member of the United Nations, Non-Aligned Movement, Arab League, African Union, and Organisation of Islamic Cooperation. Miṣr is the Classical Quranic Arabic and modern name of Egypt. The name is of Semitic origin, directly cognate with other Semitic words for Egypt such as the Hebrew מִצְרַיִם, the oldest attestation of this name for Egypt is the Akkadian
One or more of the preceding sentences incorporates text from a publication now in the public domain: Rudler, Frederick William (1911). "Amethyst". In Chisholm, Hugh. Encyclopædia Britannica. 1 (11th ed.). Cambridge University Press. p. 852.
One or more of the preceding sentences incorporates text from a publication now in the 