1.
The Black Onyx
–
The Black Onyx is a 1984 role-playing video game released in Japan, developed by Bullet-Proof Software, with development led by Henk Rogers. It was one of the first successful Japanese-language RPGs, having sold 150,000 copies and it was originally released for the NEC PC-8801, and ported to several other platforms. The Famicom version featured completely redesigned gameplay, a new map, because of memory limitations, another part of the game was released separately on some platforms as The Fire Crystal. Two other parts were announced, The Moonstone, and Arena, the SG-1000 version was one of the last official releases for that console, succeeded only by Portrait of Loretta. The player can create a party, or can ask friendly encounters to join the party to fill empty slots. The party will explore the dungeons under the town of Utsuro to obtain the legendary Black Onyx, doing so will break the curse which binds the town in eternal night. The combat system has no concept of distance, so there are no bows or similar missile weapons, there are melee weapons, shields, and armor, however. The hospital in town can offer examinations which display the PCs stats, there is a bank in town where the heroes can deposit money. This protects money from thieves, but there is no interest on the deposits, the labyrinth under the town has several entrances, each hidden in one of the locations of the town. The labyrinth has six floors corresponding to the six colors the computer can display and these must be solved in the proper order in order to create the stairway to the Black Tower, where the Onyx resides. The Black Onyx at MobyGames The Dragon Invasion, How the role-playing game came to Japan
The Black Onyx
–
European cover art for the
MSX version of The Black Onyx.
2.
Chemical formula
–
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
Chemical formula
–
Al 2 (SO 4) 3
3.
Crystal system
–
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
Crystal system
–
Hexagonal
hanksite crystal, with three-fold c-axis symmetry
Crystal system
–
The
diamond crystal structure belongs to the face-centered
cubic lattice, with a repeated 2-atom pattern.
4.
Hexagonal
–
In geometry, a hexagon is a six sided polygon or 6-gon. The total of the angles of any hexagon is 720°. A regular hexagon has Schläfli symbol and can also be constructed as an equilateral triangle, t. A regular hexagon is defined as a hexagon that is both equilateral and equiangular and it is bicentric, meaning that it is both cyclic and tangential. The common length of the sides equals the radius of the circumscribed circle, all internal angles are 120 degrees. A regular hexagon has 6 rotational symmetries and 6 reflection symmetries, the longest diagonals of a regular hexagon, connecting diametrically opposite vertices, are twice the length of one side. Like squares and equilateral triangles, regular hexagons fit together without any gaps to tile the plane, the cells of a beehive honeycomb are hexagonal for this reason and because the shape makes efficient use of space and building materials. The Voronoi diagram of a triangular lattice is the honeycomb tessellation of hexagons. It is not usually considered a triambus, although it is equilateral, the maximal diameter, D is twice the maximal radius or circumradius, R, which equals the side length, t. The minimal diameter or the diameter of the circle, d, is twice the minimal radius or inradius. If a regular hexagon has successive vertices A, B, C, D, E, F, the regular hexagon has Dih6 symmetry, order 12. There are 3 dihedral subgroups, Dih3, Dih2, and Dih1, and 4 cyclic subgroups, Z6, Z3, Z2 and these symmetries express 9 distinct symmetries of a regular hexagon. John Conway labels these by a letter and group order, r12 is full symmetry, and a1 is no symmetry. These two forms are duals of each other and have half the order of the regular hexagon. The i4 forms are regular hexagons flattened or stretched along one symmetry direction and it can be seen as an elongated rhombus, while d2 and p2 can be seen as horizontally and vertically elongated kites. G2 hexagons, with sides parallel are also called hexagonal parallelogons. Each subgroup symmetry allows one or more degrees of freedom for irregular forms, only the g6 subgroup has no degrees of freedom but can seen as directed edges. Hexagons of symmetry g2, i4, and r12, as parallelogons can tessellate the Euclidean plane by translation, other hexagon shapes can tile the plane with different orientations
Hexagonal
–
Giants causeway closeup
Hexagonal
–
A regular hexagon
Hexagonal
–
The ideal crystalline structure of
graphene is a hexagonal grid.
Hexagonal
–
Assembled
E-ELT mirror segments
5.
Trigonal
–
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
Trigonal
–
Example trigonal crystals (
quartz)
Trigonal
–
Example trigonal rhombohedral crystals (
dolomite)
6.
Cleavage (crystal)
–
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
Cleavage (crystal)
–
Green
fluorite with prominent cleavage.
Cleavage (crystal)
–
Biotite with basal cleavage.
7.
Fracture (mineralogy)
–
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
Fracture (mineralogy)
–
Obsidian
Fracture (mineralogy)
–
Limonite
Fracture (mineralogy)
–
Native copper
Fracture (mineralogy)
–
Chrysotile
8.
Mohs scale of mineral hardness
–
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
Mohs scale of mineral hardness
Mohs scale of mineral hardness
Mohs scale of mineral hardness
Mohs scale of mineral hardness
9.
Lustre (mineralogy)
–
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
Lustre (mineralogy)
–
Cut diamonds.
Lustre (mineralogy)
–
Kaolinite
Lustre (mineralogy)
–
Moss
opal
Lustre (mineralogy)
–
Pyrite
10.
Streak (mineralogy)
–
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
Streak (mineralogy)
–
Streak plates with
pyrite (left) and
rhodochrosite (right)
11.
Transparency and translucency
–
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
Transparency and translucency
–
Dichroic filters are created using optically transparent materials.
Transparency and translucency
–
Translucency of a material being used to highlight the structure of a photographic subject
Transparency and translucency
–
Meiningen Catholic Church, 20th century glass
Transparency and translucency
–
A laser beam bouncing down an
acrylic rod, illustrating the total internal reflection of light in a multimode optical fiber
12.
Specific gravity
–
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
Specific gravity
–
Testing specific gravity of fuel.
13.
Refractive index
–
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
Refractive index
–
Thomas Young coined the term index of refraction.
Refractive index
–
A
ray of light being
refracted in a plastic block.
Refractive index
–
Diamonds have a very high refractive index of 2.42.
Refractive index
–
A
split-ring resonator array arranged to produce a negative index of refraction for
microwaves.
14.
Oxide mineral
–
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
Oxide mineral
–
Oxide mineral exhibit at the Museum of Geology in South Dakota
15.
Chalcedony
–
Chalcedony is a cryptocrystalline form of silica, composed of very fine intergrowths of quartz and moganite. These are both silica minerals, but they differ in that quartz has a crystal structure, while moganite is monoclinic. Chalcedonys standard chemical structure is SiO2, Chalcedony has a waxy luster, and may be semitransparent or translucent. It can assume a range of colors, but those most commonly seen are white to gray. The color of chalcedony sold commercially is often enhanced by dyeing or heating, the name chalcedony comes from the Latin chalcedonius. The name appears in Pliny the Elders Naturalis Historia as a term for a kind of Jaspis. The name is derived from the town Chalcedon in Asia Minor. The Greek word khalkedon also appears in the Book of Revelation and it is a hapax legomenon so it is hard to tell whether the precious gem mentioned in the Bible is the same mineral known by this name today. Chalcedony occurs in a range of varieties. Many semi-precious gemstones are in forms of chalcedony. The more notable varieties of chalcedony are as follows, Agate is a variety of chalcedony characterized by either transparency or color patterns, opaque varieties are sometimes referred to as jasper. Fire agate shows iridescent phenomena on a background, iris agate shows exceptional iridescence when light is shone through the stone. Landscape agate is chalcedony with a number of different mineral impurities making the stone resemble landscapes, aventurine is a form of quartz, characterised by its translucency and the presence of platy mineral inclusions that give a shimmering or glistening effect termed aventurescence. Chrome-bearing fuchsite is the inclusion, and gives a silvery green or blue sheen. Oranges and browns are attributed to hematite or goethite, carnelian is a clear-to-translucent reddish-brown variety of chalcedony. Its hue may vary from an orange, to an intense almost-black coloration. Similar to carnelian is sard, which is rather than red. Chrysoprase is a variety of chalcedony, which has been colored by nickel oxide
Chalcedony
–
A cut and polished Chalcedony
geode
Chalcedony
–
Agate
Chalcedony
–
Aventurine (Unknown scale)
Chalcedony
–
Carnelian
16.
Agate
–
Agate /ˈæɡət/ is a cryptocrystalline variety of silica, chiefly chalcedony, characterised by its fineness of grain and brightness of color. Although agates may be found in various kinds of rock, they are associated with volcanic rocks. Colorful agates and other chalcedonies were obtained over 3,000 years ago from the Achates River, Agate has also been known to fill veins or cracks in volcanic or altered rock underlain by granitic intrusive masses. Such agates, when cut transversely, exhibit a succession of lines, often of extreme tenuity. Such stones are known as banded agate, riband agate and striped agate, perhaps the most comprehensive review of agate chemistry is a recent text by Moxon cited below. This green silicate may give rise by alteration to a iron oxide. The outer surface of an agate, freed from its matrix, is pitted and rough. The first layer spread over the wall of the cavity has been called the priming, when the matrix in which the agates are embedded disintegrates, they are set free. The agates are extremely resistant to weathering and remain as nodules in the soil, or are deposited as gravel in streams, a Mexican agate, showing only a single eye, has received the name of cyclops agate. Dendritic agates have fern like patterns in them formed due to the presence of manganese, other types of included matter deposited during agate-building include sagenitic growths and chunks of entrapped detritus. Occasionally agate fills a void left by decomposed vegetative material such as a limb or root and is called limb cast agate due to its appearance. Enhydro agate contains tiny inclusions of water, sometimes with air bubbles, turritella agate is formed from silicified fossil Elimia tenera shells. E. tenera are spiral freshwater gastropods having elongated, spiral shells composed of many whorls, similarly, coral, petrified wood and other organic remains or porous rocks can also become agatized. Agatized coral is often referred to as Petoskey stone or agate, greek agate is a name given to pale white to tan colored agate found in Sicily back to 400 BC. The Greeks used it for making jewelry and beads, brazilian agate is found as sizable geodes of layered nodules. These occur in brownish tones interlayered with white and gray, quartz forms within these nodules, creating a striking specimen when cut opposite the layered growth axis. It is often dyed in various colors for ornamental purposes, certain stones, when examined in thin sections by transmitted light, show a diffraction spectrum due to the extreme delicacy of the successive bands, whence they are termed rainbow agates. Often agate coexists with layers or masses of opal, jasper or crystalline quartz due to ambient variations during the formation process, lace agate is a variety that exhibits a lace-like pattern with forms such as eyes, swirls, bands or zigzags
Agate
–
Banded agate (agate-like
onyx); the specimen is 2.5 cm (0.98 in) wide
Agate
–
Botswana agate
Agate
–
Agatized Coral
Agate
–
"Turritella agate" (
Elimia tenera) from Green River Formation, Wyoming
17.
Quartz
–
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
Quartz
–
Quartz
crystal cluster from
Tibet
Quartz
–
Clear rock crystals on a white base
Quartz
–
Amethyst crystals on matrix
Quartz
–
Citrine from Brazil
18.
Lapidary
–
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
Lapidary
–
A rural Thai gem cutter (1988 photograph)
Lapidary
–
Lapidary tool kit from around 900 AD,
Chaco Culture National Historical Park
Lapidary
–
A jewellery worker in Sri Lanka (2006 photograph)
19.
Calcite
–
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate. The Mohs scale of hardness, based on scratch hardness comparison. Other polymorphs of calcium carbonate are the minerals aragonite and vaterite, aragonite will change to calcite at 380–470 °C, and vaterite is even less stable. Calcite is derived from the German Calcit, a term coined in the 19th century from the Latin word for lime and it is thus etymologically related to chalk. Calcite crystals are trigonal-rhombohedral, though actual calcite rhombohedra are rare as natural crystals, however, they show a remarkable variety of habits including acute to obtuse rhombohedra, tabular forms, prisms, or various scalenohedra. Calcite exhibits several twinning types adding to the variety of observed forms and it may occur as fibrous, granular, lamellar, or compact. Cleavage is usually in three directions parallel to the rhombohedron form and its fracture is conchoidal, but difficult to obtain. It has a defining Mohs hardness of 3, a gravity of 2.71. Color is white or none, though shades of gray, red, orange, yellow, green, blue, violet, brown, calcite is transparent to opaque and may occasionally show phosphorescence or fluorescence. A transparent variety called Iceland spar is used for optical purposes, acute scalenohedral crystals are sometimes referred to as dogtooth spar while the rhombohedral form is sometimes referred to as nailhead spar. Single calcite crystals display an optical property called birefringence and this strong birefringence causes objects viewed through a clear piece of calcite to appear doubled. The birefringent effect was first described by the Danish scientist Rasmus Bartholin in 1669, at a wavelength of ~590 nm calcite has ordinary and extraordinary refractive indices of 1.658 and 1.486, respectively. Between 190 and 1700 nm, the refractive index varies roughly between 1.9 and 1.5, while the extraordinary refractive index varies between 1.6 and 1.4. Calcite, like most carbonates, will dissolve with most forms of acid, calcite can be either dissolved by groundwater or precipitated by groundwater, depending on several factors including the water temperature, pH, and dissolved ion concentrations. Although calcite is fairly insoluble in water, acidity can cause dissolution of calcite. Ambient carbon dioxide, due to its acidity, has a slight solubilizing effect on calcite, calcite exhibits an unusual characteristic called retrograde solubility in which it becomes less soluble in water as the temperature increases. When conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together or it can fill fractures. On a landscape scale, continued dissolution of calcium carbonate-rich rocks can lead to the expansion and eventual collapse of cave systems, high-grade optical calcite was used in World War II for gun sights, specifically in bomb sights and anti-aircraft weaponry
Calcite
–
A one-inch calcite
rhomb that shows the
double image refraction property
Calcite
–
Crystal structure of calcite
Calcite
–
faceted calcite, oval cut, 1.12ct, Mexico.
Calcite
–
Doubly terminated calcite crystal.
20.
Carbonate
–
In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, a polyatomic ion with the formula of CO2−3. The name may mean an ester of carbonic acid, an organic compound containing the carbonate group C2. In geology and mineralogy, the term carbonate can refer both to carbonate minerals and carbonate rock, and both are dominated by the ion, CO2−3. Carbonate minerals are extremely varied and ubiquitous in chemically precipitated sedimentary rock, sodium carbonate and potassium carbonate have been used since antiquity for cleaning and preservation, as well as for the manufacture of glass. Carbonates are widely used in industry, e. g. in iron smelting, as a raw material for Portland cement and lime manufacture, in the composition of ceramic glazes, the carbonate ion is the simplest oxocarbon anion. It consists of one carbon atom surrounded by three oxygen atoms, in a planar arrangement, with D3h molecular symmetry. It has a mass of 60.01 g/mol and carries a total formal charge of −2. It is the base of the hydrogen carbonate ion, HCO−3. The Lewis structure of the ion has two single bonds to negative oxygen atoms, and one short double bond to a neutral oxygen. This structure is incompatible with the symmetry of the ion. This process is called calcination, after calx, the Latin name of quicklime or calcium oxide, CaO, exceptions include lithium, sodium, potassium and ammonium carbonates, as well as many uranium carbonates. In aqueous solution, carbonate, bicarbonate, carbon dioxide, in strongly basic conditions, the carbonate ion predominates, while in weakly basic conditions, the bicarbonate ion is prevalent. In more acid conditions, aqueous carbon dioxide, CO2, is the main form, thus sodium carbonate is basic, sodium bicarbonate is weakly basic, while carbon dioxide itself is a weak acid. Carbonated water is formed by dissolving CO2 in water under pressure, in living systems an enzyme, carbonic anhydrase, speeds the interconversion of CO2 and carbonic acid. Although the carbonate salts of most metals are insoluble in water, in solution this equilibrium between carbonate, bicarbonate, carbon dioxide and carbonic acid changes consonant to changing temperature and pressure conditions. In the case of ions with insoluble carbonates, e. g. CaCO3. This is an explanation for the buildup of scale inside pipes caused by hard water, in organic chemistry a carbonate can also refer to a functional group within a larger molecule that contains a carbon atom bound to three oxygen atoms, one of which is double bonded. These compounds are known as organocarbonates or carbonate esters, and have the general formula ROCOOR′
Carbonate
–
Carbonate
21.
Pliny the Elder
–
In the latter number will be my uncle, by virtue of his own and of your compositions. Pliny is referring to the fact that Tacitus relied on his uncles now missing work on the History of the German Wars. The wind caused by the sixth and largest pyroclastic surge of the eruption would not allow his ship to leave the shore, and Pliny probably died during this event. Plinys dates are pinned to the eruption of Mount Vesuvius in AD79 and a statement of his nephew that he died in his 56th year, Pliny was the son of an equestrian, Gaius Plinius Celer, and his wife, Marcella. Neither the younger nor the elder Pliny mention the names and their ultimate source is a fragmentary inscription found in a field in Verona and recorded by the 16th century Augustinian monk Onofrio Panvinio at Verona. The reading of the inscription depends on the reconstruction, but in all cases the names come through, whether he was an augur and whether she was named Grania Marcella are less certain. Jean Hardouin presents a statement from a source that he claims was ancient, that Pliny was from Verona. Hardouin also cites the conterraneity of Catullus, additional efforts to connect Celer and Marcella with other gentes are highly speculative. Hardouin is the scholar to use his unknown source. He kept statues of his ancestors there, a statue of Pliny on the facade of the Duomo of Como celebrates him as a native son. He had a sister, Plinia, who married into the Caecilii and was the mother of his nephew, Pliny the Younger, whose letters describe his work and study regimen in detail. In one of his letters to Tacitus, Pliny the Younger details how his uncles breakfasts would be light and simple following the customs of our forefathers. This shows that Pliny the Younger wanted it to be conveyed that Pliny the Elder was a good Roman and this statement would have pleased Tacitus. Two inscriptions identifying the hometown of Pliny the Younger as Como take precedence over the Verona theory, one commemorates the youngers career as imperial magistrate and details his considerable charitable and municipal expenses on behalf of the people of Como. Another identifies his father Lucius village as Fecchio near Como and it is likely therefore that Plinia was a local girl and Pliny the Elder, her brother, was from Como. Gaius was a member of the Plinii gens and he did not take his fathers cognomen, Celer, but assumed his own, Secundus. As his adopted son took the same cognomen, Pliny founded a branch, no earlier instances of the Plinii are known. In 59 BC, only about 82 years before Plinys birth, Julius Caesar founded Novum Comum as a colonia to secure the region against the Alpine tribes, whom he had been unable to defeat
Pliny the Elder
–
One of the
Xanten Horse-Phalerae located in the
British Museum, measuring 10.5 cm (4.1 in). It bears an inscription formed from punched dots: PLINIO PRAEF EQ; i.e., Plinio praefecto equitum, "Pliny prefect of cavalry". It was perhaps issued to every man in Pliny's unit. The figure is the bust of the emperor.
Pliny the Elder
–
Pliny the Elder, as imagined by a 19th-century artist. No contemporary depiction of Pliny is known to survive.
Pliny the Elder
–
City and Lake of
Como, painted by
Jean-Baptiste-Camille Corot, 1834.
Pliny the Elder
–
The temple of
Castor and Pollux in Rome
22.
Sulfuric acid
–
Sulfuric acid is a highly corrosive strong mineral acid with the molecular formula H2SO4 and molecular weight 98.079 g/mol. It is a pungent-ethereal, colorless to slightly yellow liquid that is soluble in water at all concentrations. Sometimes, it is dyed dark brown during production to alert people to its hazards, the historical name of this acid is oil of vitriol. Sulfuric acid is an acid and shows different properties depending upon its concentration. Its corrosiveness on other materials, like metals, living tissues or even stones, can be ascribed to its strong acidic nature and, if concentrated. It is also hygroscopic, readily absorbing water vapour from the air, Sulfuric acid at a high concentration can cause very serious damage upon contact, since not only does it cause chemical burns via hydrolysis, but also secondary thermal burns through dehydration. It can lead to permanent blindness if splashed onto eyes and irreversible damage if swallowed, Sulfuric acid has a wide range of applications including in domestic acidic drain cleaners, as an electrolyte in lead-acid batteries and in various cleaning agents. It is also a central substance in the chemical industry, principal uses include mineral processing, fertilizer manufacturing, oil refining, wastewater processing, and chemical synthesis. It is widely produced with different methods, such as process, wet sulfuric acid process, lead chamber process. The study of vitriol, a category of glassy minerals from which the acid can be derived, sumerians had a list of types of vitriol that they classified according to the substances color. Some of the earliest discussions on the origin and properties of vitriol is in the works of the Greek physician Dioscorides, galen also discussed its medical use. Ibn Sina focused on its uses and different varieties of vitriol. Sulfuric acid was called oil of vitriol by medieval European alchemists because it was prepared by roasting green vitriol in an iron retort, there are references to it in the works of Vincent of Beauvais and in the Compositum de Compositis ascribed to Saint Albertus Magnus. A passage from Pseudo-Geber´s Summa Perfectionis was long considered to be the first recipe for sulfuric acid, in the seventeenth century, the German-Dutch chemist Johann Glauber prepared sulfuric acid by burning sulfur together with saltpeter, in the presence of steam. As saltpeter decomposes, it oxidizes the sulfur to SO3, in 1736, Joshua Ward, a London pharmacist, used this method to begin the first large-scale production of sulfuric acid. This process allowed the effective industrialization of sulfuric acid production, after several refinements, this method, called the lead chamber process or chamber process, remained the standard for sulfuric acid production for almost two centuries. Sulfuric acid created by John Roebucks process approached a 65% concentration, later refinements to the lead chamber process by French chemist Joseph Louis Gay-Lussac and British chemist John Glover improved concentration to 78%. However, the manufacture of dyes and other chemical processes require a more concentrated product
Sulfuric acid
–
Sulfuric acid
Sulfuric acid
Sulfuric acid
–
John Dalton 's 1808 sulfuric acid molecule shows a central
sulfur atom bonded to three oxygen atoms, or
sulfur trioxide, the
anhydride of sulfuric acid.
Sulfuric acid
–
Drops of concentrated sulfuric acid rapidly decompose a piece of cotton towel by dehydration.
23.
Hydrochloric acid
–
Hydrochloric acid is a corrosive, strong mineral acid with many industrial uses. A colorless, highly pungent solution of chloride in water. Free hydrochloric acid was first formally described in the 16th century by Libavius, later, it was used by chemists such as Glauber, Priestley, and Davy in their scientific research. It has numerous applications, including household cleaning, production of gelatin and other food additives, descaling. About 20 million tonnes of acid are produced worldwide annually. It is also found naturally in gastric acid, Hydrochloric acid was known to European alchemists as spirits of salt or acidum salis. Both names are used, especially in other languages, such as German, Salzsäure, Dutch, Zoutzuur, Swedish, Saltsyra, Turkish, Tuz Ruhu, Polish, kwas solny and Chinese. Gaseous HCl was called marine acid air, the old name muriatic acid has the same origin, and this name is still sometimes used. The name hydrochloric acid was coined by the French chemist Joseph Louis Gay-Lussac in 1814, aqua regia, a mixture consisting of hydrochloric and nitric acids, prepared by dissolving sal ammoniac in nitric acid, was described in the works of Pseudo-Geber, a 13th-century European alchemist. Other references suggest that the first mention of aqua regia is in Byzantine manuscripts dating to the end of the 13th century, free hydrochloric acid was first formally described in the 16th century by Libavius, who prepared it by heating salt in clay crucibles. Joseph Priestley of Leeds, England prepared pure hydrogen chloride in 1772, during the Industrial Revolution in Europe, demand for alkaline substances increased. A new industrial process developed by Nicolas Leblanc of Issoundun, France enabled cheap large-scale production of sodium carbonate, in this Leblanc process, common salt is converted to soda ash, using sulfuric acid, limestone, and coal, releasing hydrogen chloride as a by-product. Until the British Alkali Act 1863 and similar legislation in other countries, after the passage of the act, soda ash producers were obliged to absorb the waste gas in water, producing hydrochloric acid on an industrial scale. In the 20th century, the Leblanc process was replaced by the Solvay process without a hydrochloric acid by-product. Since hydrochloric acid was already settled as an important chemical in numerous applications. After the year 2000, hydrochloric acid is made by absorbing by-product hydrogen chloride from industrial organic compounds production. Hydrochloric acid is the salt of hydronium ion, H3O+ and chloride and it is usually prepared by treating HCl with water. H C l + H2 O ⟶ H3 O + + C l − Hydrochloric acid can therefore be used to prepare salts called chlorides, Hydrochloric acid is a strong acid, since it is completely dissociated in water
Hydrochloric acid
–
Hydrochloric acid
24.
Gemma Augustea
–
The Gemma Augustea is a low-relief cameo engraved gem cut from a double-layered Arabian onyx stone. It is commonly agreed that the gem cutter who created the Gemma Augustea was either Dioscurides or one of his disciples, the Gemma Augustea is a low-relief cameo engraved gem cut from a double-layered Arabian onyx stone. One layer is white, while the other is bluish-brown, the painstaking method by which the stone was cut allowed minute detail with sharp contrast between the images and background, also allowing for a great deal of shadow play. The size of the gem also made for easier manipulation and a grander scene and it stands 7.5 inches tall with a width of 9 inches and an average thickness of 0.5 inches. It is commonly agreed that the gem cutter who created Gemma Augustea was either Dioscurides or one of his disciples, Dioscurides was Caesar Augustus’ favorite gem cutter, and his work and copies of it are seen from all over the ancient Roman world. The gem is set as though in the period c, AD 10–20, although some scholars believe it to have been created decades later because of their interpretation of the scene. If Dioscurides, or cutters following his example, made it, at some time in antiquity it moved to Byzantium, perhaps after Constantine I had officially moved the capital of the empire there. If this gem was made during his lifetime, it would perhaps have been made as a gift to a family in a Roman province or client kingdom. Alternatively, if the gem was made after Augustus’ death, the identity of one or more of the portraits may be different from the usual identification. Another viewpoint is that the gem does portray Augustus as a god in his lifetime, similar issues arise with other Imperial cameos such as the Blacas Cameo in the British Museum. In 1533, Francis I of France appropriated it and moved it to Paris, not long thereafter it was sold for 12,000 ducats to Rudolph II, Holy Roman Emperor. During the 17th century, it was set in German gold and this setting shows that the gem must have been damaged, the upper left side being broken with at least one other figure missing, probably before Rudolph II bought it, but definitely before 1700. The gem is now in the Kunsthistorisches Museum in Vienna, the throned figure, #1 in the numbered illustration, is usually taken to be Augustus, although in some interpretations, it could represent a later Roman ruler. Figure #3 is the most readily identifiable, having characteristics held by no other, the woman is Oikoumene - the personification of the inhabited world. This inhabited or civilized world is either that of the early Roman Empire and she wears upon her head a mural crown and veil. She is crowning figure #1 with the corona civica of oak leaves - used to someone for saving the life of a Roman citizen. In this grand scale depiction, however, it is given to figure #1 because he saved a multitude of Roman citizens, Figure #5 and #6 seem to be closely related. Figure #5 is Oceanus or Neptune whose significance is often seen as one balancing the scene across from #4 and #7, below him is a reclined personification of either Gaia or Italia Turrita
Gemma Augustea
–
Gemma Augustea
Gemma Augustea
–
Gemma Augustea, with reference numbers.
Gemma Augustea
–
The lower register
Gemma Augustea
–
Key to lower register
25.
Cameo (carving)
–
Cameo is a method of carving an object such as an engraved gem, item of jewellery or vessel made in this manner. It nearly always features a relief image, contrast with intaglio. Today the term may be used loosely for objects with no colour contrast. This derives from another generalized meaning that has developed, the cameo as an image of a head in a frame in any medium. In cheaper modern work, shell and glass are more common, glass cameo vessels, such as the famous Portland Vase, were also developed by the Romans. Modern cameos can be produced by setting a carved relief, such as a portrait and this is called an assembled cameo. Sometimes dyes are used to enhance these colours, sir Wallis Budge alleged that the noun Cameo apparently comes from Kameo, a word used in kabbalistic slang to signify a magical square, i. e. A kind of talisman whereupon magical spells was carved, stone cameos of great artistry were made in Greece dating back as far as the 3rd century BC. The Farnese Tazza is the oldest major Hellenistic piece surviving and they were very popular in Ancient Rome, especially in the family circle of Augustus. Roman Cameos became less common around in the leading up to 300AD although production continued at a much reduced rate right through the Middle Ages. The technique has since enjoyed periodic revivals, notably in the early Renaissance, the Neoclassical revival began in France with Napoleons support of the glyptic arts, and even his coronation crown was decorated with cameos. In 1852 Théophile Gautier titled a collection of his highly polished, during the Roman period the cameo technique was used on glass blanks, in imitation of objects being produced in agate or sardonyx. Cameo glass objects were produced in two periods, between around 25 BC and 50/60 AD, and in the later Empire around the mid-third and mid-fourth century. Roman glass cameos are rare objects, with only two hundred fragments and sixteen complete pieces known, only one of which dates from the later period. Blanks could be produced by fusing two separately cast sheets of glass, or by dipping the base glass into a crucible of molten overlay glass during blowing, the most famous example of a cameo from the early period is the Portland Vase. Although occasionally used in Roman cameos, the earliest prevalent use of shell for carving was during the Renaissance. Before that time, cameos were carved from hardstone, the Renaissance cameos are typically white on a grayish background and were carved from the shell of a mussel or cowry, the latter a tropical mollusk. In the mid 18th century, explorations revealed new shell varieties, helmet shells from the West Indies, and queen conch shells from the Bahamas and West Indies, arrived in Europe
Cameo (carving)
–
The
Great Cameo of France, five layers
sardonyx,
Rome, ca 23 A.D., the largest of Antiquity
Cameo (carving)
–
Renaissance cameo of an African king, 16th century, Italy(?) (
Cabinet des médailles)
Cameo (carving)
–
Woman wearing a cameo at her throat, on a high lace collar in the Edwardian style.
Cameo (carving)
–
Cameo, handmade shell (Cassis madascarensis), Modula Gioielli.
26.
Engraved gem
–
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
Engraved gem
–
Roman intaglio portrait of
Caracalla in
amethyst, once in the Treasury of
Sainte-Chapelle, when it was adapted by adding an inscription and cross to represent
Saint Peter.
Engraved gem
–
Cameo of a Roman prince
Engraved gem
–
Antelopes attacked by birds:
cylinder seal in
hematite and its impression. Late Bronze Age II (maybe 14th century BC), from
Cyprus in the
Minoan period, following Near Eastern precedents.
Engraved gem
–
Reclining
satyr,
Etruscan c. 550 BC, 2.2 cm wide. Note the vase shown "sideways"; it is characteristic of early gems that not all elements in the design are read from the same direction of view.
27.
Hardstone carving
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Normally the objects are small, and the category overlaps with both jewellery and sculpture. Hardstone carving is sometimes referred to by the Italian term pietre dure, however, pietre dura is the term used for stone inlay work. Hardstone carving falls under the category of glyptic art, which covers small carvings. These are typically not capable of a finish in very small carvings. In other contexts, such as architecture, hard stone and soft stone have different meanings, referring to actual measured hardness using the Mohs scale of mineral hardness, essentially, any stone that is often used in jewellery is likely to count as a hardstone. Hard organic minerals such as amber and jet are included, as well as the mineraloid obsidian, hardstones normally have to be drilled rather than worked with edged tools to achieve a fine finish. The various materials called jade have been dominant in East Asian and Mesoamerican carving, stones typically used for buildings and large sculpture are not often used for small objects such as vessels, although this does occur. These are found from the Neolithic Liangzhu culture onwards, and blades from the 2nd millennium BCE Shang Dynasty on, traditional Chinese culture attaches strong powers to jade, the jade burial suits in which aristocrats of the Han Dynasty were buried were intended to preserve the body from decay. The English word jade derives from the Aztec belief that the mineral cured ailments of the kidneys, in general whiteish nephrite jade was the most highly regarded in China until about 1800, when the deeper and brighter green of the best jadeite became more highly favoured. There are related Asian traditions of Korean jade carving, in Southeast Asia and, to a lesser extent. Smallish Sassanian carvings are known, mostly for seals or jewellery, Egyptian carving of rock crystal into vessels appears in the late 10th century, and virtually disappears after about 1040. The rock crystal used in Egypt was apparently traded from East Africa, islamic jades and other carvings reached a particular peak in the Mughal Empire, where apart from portable carvings inlaid panels of carved stones were included in buildings such as the Taj Mahal. The great wealth of the Mughal court allowed precious stones like rubies, the court workshops of the Ottoman Empire also produced lavish and elaborate objects, in similar styles but without reaching the artistic peaks of Mughal carving. The jade signet ring of Tutankhamun has been called a specimen of Egyptian jade. From the Hellenistic period elaborate vessels in semi-precious stone begin to appear, mostly carved, the best collection of Byzantine liturgical vessels is in the Treasury of San Marco, Venice, some of them booty from the Fourth Crusade. Byzantine artists maintained a tradition throughout the Middle Ages, often working in rock crystal. By the end of the Middle Ages a wider variety of stones and objects are seen and they also produced vessels and small sculptures from a single piece of stone, often mounted with gold, which was also a speciality of Milanese workshops. Other rulers followed their example, including Peter the Great, whose Peterhof Lapidary Works, founded in 1721, began the passion among Russian royalty and aristocrats for hardstones
Hardstone carving
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Mughal dagger hilt in
jade with gold,
rubies, and
emeralds.
Hardstone carving
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Dish of
serpentine with inlaid gold fish, 1st century BCE or CE, with 9th-century mounts
Hardstone carving
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Han Dynasty jade
bi
Hardstone carving
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Fatimid carved rock crystal ewer, c. 1000, with 11th-century Italian lid.
28.
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
Jewelry
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Amber pendants
Jewelry
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Diamond temptation design
Jewelry
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The Queen
Farida of Egypt red coral parure by Ascione manufacture, 1938, Naples,
Coral Jewellery Museum
Jewelry
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The
Daria-i-Noor (meaning: Sea of Light) Diamond from the collection of the national jewels of Iran at
Central Bank of Islamic Republic of Iran
29.
Cabochon
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A cabochon, from the Middle French word caboche, is a gemstone which has been shaped and polished as opposed to faceted. The resulting form is usually a convex obverse with a flat reverse, cutting en cabochon is usually applied to opaque gems, while faceting is usually applied to transparent stones. Hardness is also taken into account as softer gemstones with a lower than 7 on the Mohs hardness scale are easily scratched, mainly by silicon dioxide in dust. This would quickly make translucent gems unattractive—instead they are polished as cabochons, the usual shape for cutting cabochons is an ellipse. An exception is cabochons on some watches crowns, which are round, the procedure is to cut a slab of the rough rock with a slab saw, and next to stencil a shape from a template. The slab is then trimmed near the line using a diamond blade saw—called a trim saw. Diamond impregnated wheels or silicon carbide wheels can be used to grind the rock down. Most lapidary workshops and production facilities have moved away from silicon carbide to diamond grinding wheels or flat lap disks, once the piece is trimmed it can be dopped or completed by hand. Dopping is normally done by adhering the stone with hard wax onto a length of wooden dowel called a dop stick, the piece is then ground to the template line, the back edges may be bevelled, and finally the top is sanded and polished to a uniform dome
Cabochon
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Moonstone cabochons in a
jewellers window
Cabochon
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A round
sapphire cabochon on the crown of a men's dress
watch.
Cabochon
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Amber pendants. The oval cabochon
pendant is 52 × 32 mm (2 × 1.3 in).
30.
Intaglio (jewelry)
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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
Intaglio (jewelry)
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Roman intaglio portrait of
Caracalla in
amethyst, once in the Treasury of
Sainte-Chapelle, when it was adapted by adding an inscription and cross to represent
Saint Peter.
Intaglio (jewelry)
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Cameo of a Roman prince
Intaglio (jewelry)
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Antelopes attacked by birds:
cylinder seal in
hematite and its impression. Late Bronze Age II (maybe 14th century BC), from
Cyprus in the
Minoan period, following Near Eastern precedents.
Intaglio (jewelry)
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Reclining
satyr,
Etruscan c. 550 BC, 2.2 cm wide. Note the vase shown "sideways"; it is characteristic of early gems that not all elements in the design are read from the same direction of view.
