Onyx

Onyx is a banded variety of the oxide mineral chalcedony . Agate and onyx are both varieties of layered chalcedony that differ only in the form of the bands: agate has curved bands and onyx has parallel bands. The colours of its bands range from white to almost every colour (save some shades, such as purple or blue). Commonly, specimens of onyx contain bands of black and/or white. Onyx is a gemstone whose description can have several connotations. Its most accepted gemstone definition describes a solid black Chalcedony, or a banded or layered black and white Chalcedony. The term Onyx is occasionally used to described any engraved stone with a solid colour base, or it may describe any banded gemstone with parallel banding. In its solid black form, Onyx is the most traditional black gemstone. Onyx is black and white banded agate (cryptocrystalline or chalcedony quartz). It should not to be confused with onyx marble, which is limestone. The banding of onyx is parallel and consistent. Some varieties of onyx differ in colour, such as sard onyx , which has a brown base and white upper layer, cornelian onyx , which has a red base and white upper layer, and niccolo onyx , which has a very thin upper layer, allowing the black base colour to show through as grey or blue. Onyx takes its name from the Greek word "onux", which means fingernail; this could be due to a Greek legend, in which Eros mischievously cut the fingernails of Aphrodite with an arrowhead whilst she slept, and the gods turned the clippings into stone. Onyx was cut and carved as a gemstone by the Ancient Greeks and Romans in cameos. Intaglio etchings (negative relief engravings) were also made from onyx. These carvings showcase the banding of onyx. The call has now and again been used, incorrectly, to label different banded lapidary substances, along with banded calcite found in Mexico, Pakistan, and different places, and often carved, polished and bought. This cloth is lots softer than true onyx, and plenty greater simply available. The majority of carved items bought as "onyx" these days are this carbonate fabric. Artificial onyx types have also been produced from common chalcedony and plain agates. The first-century naturalist Pliny the Elder described these techniques being used in Roman times. Treatments for producing black and other colours include soaking or boiling chalcedony in sugar solutions, then treating with sulphuric or hydrochloric acid to carbonize sugars which had been absorbed into the top layers of the stone. These techniques are still used, as well as other dyeing treatments, and most so-called "black onyx" sold is artificially treated. In addition to dye treatments, heating and treatment with nitric acid have been used to lighten or eliminate undesirable colours. Onyx deposits are discovered in countries all around the world, which include Argentina, Australia, Brazil, India, Botswana, Madagascar, Mexico, Myanmar (Burma), Pakistan, Sri Lanka, Uruguay and the united states. Onyx may be recognized through its black base and white top layer with parallel banding. However, inside the case of sard onyx the bottom is brown and cornelian onyx has a pink base. It is hard to become aware of while the material is a unmarried colour and can simplest be certainly outstanding from agate whilst seen in the tough, displaying visibly parallel and constant banding. It has a long history of use for hardstone carving and jewellery, where it is usually cut as a cabochon or into beads. It has also been used for intaglio and hardstone cameo engraved gems, where the bands make the image contrast with the ground. Some onyx is natural but much of the material in commerce is produced by the staining of agate. Onyx turned into utilized in Egypt as early as the Second Dynasty to make bowls and other pottery gadgets. Use of sardonyx seems in the artwork of Minoan Crete, notably from the archaeological recoveries at Knossos. Brazilian green onyx was often used as plinths for art decorative sculptures created in the 1920s and 1930s. The German sculptor Ferdinand Preiss used Brazilian green onyx for the base on the majority of his chryselephantine sculptures. Green onyx was also used for trays and pin dishes produced mainly in Austria often with small bronze animals or figures attached. Onyx is mentioned in the Bible many times. Sardonyx (onyx in which white layers alternate with sard) is mentioned in the Bible as well. Onyx was known to the Ancient Greeks and Romans. The first-century naturalist Pliny the Elder described both type of onyx and various artificial treatment techniques in his Naturalis Historia. Slabs of onyx (from the Atlas Mountains) were famously utilized by Mies van der Rohe in Villa Tugendhat at Brno (completed 1930) to create a shimmering semi-translucent interior wall. The H?Tel de la Pa?Va in Paris is cited for its yellow onyx d?Cor, and the new Mariinsky Theatre Second Stage in Moscow uses yellow onyx within the foyer. Chemical Formula SiO 2 Colour White, Black, Banded Hardness 7 Crystal System Hexagonal Refractive Index 1.54 - 1.55 SG 2.63 - 2.65 Transparency Translucent to opaque Double Refraction .009 Luster Vitreous Cleavage Indiscernible Mineral Class Quartz (Chalcedony)
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