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Onyx primarily refers to the parallel banded variety of the silicate mineral
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 trigonal crystal structure, while moganite is monoclinic. Chalce ...
. Agate and onyx are both varieties of layered
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 trigonal crystal structure, while moganite is monoclinic. Chalce ...
that differ only in the form of the bands: agate has curved bands and onyx has parallel bands. The colors of its bands range from black to almost every color. Commonly, specimens of onyx contain bands of black and/or white. Onyx, as a descriptive term, has also been applied to parallel banded varieties of alabaster, marble, obsidian and opal, and misleadingly to materials with contorted banding, such as "Cave Onyx" and "Mexican Onyx".


Etymology

''Onyx'' comes through Latin (of the same spelling), from the Greek ὄνυξ, meaning "claw" or "fingernail". Onyx with flesh-colored and white bands can sometimes resemble a fingernail. The English word "nail" is
cognate In linguistics, cognates, also called lexical cognates, are words that have a common etymology, etymological origin. Cognates are often inherited from a proto-language, shared parent language, but they may also involve loanword, borrowings from ...
with the Greek word.


Varieties

Onyx is formed of bands of chalcedony in alternating colors. It is cryptocrystalline, consisting of fine intergrowths of the
silica
silica
minerals
quartz Quartz is a hard, crystalline mineral composed of silicon and oxygen atoms. The atoms are linked in a continuous framework of SiO4 silicon-oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tetrahedra, ...
and
moganite
moganite
. Its bands are parallel to one another, as opposed to the more chaotic banding that often occurs in agates. Sardonyx is a variant in which the colored bands are sard (shades of red) rather than black. Black onyx is perhaps the most famous variety, but is not as common as onyx with colored bands. Artificial treatments have been used since ancient times to produce both the black color in "black onyx" and the reds and yellows in sardonyx. Most "black onyx" on the market is artificially colored.


Imitations and treatments

The name has also commonly been used to label other banded materials, such as banded
calcite Image:Calcite.png, 235px, Crystal structure of calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). The Mohs scale of mineral hardness, based on Scr ...

calcite
found in
Mexico Mexico ( es, México ; Nahuan languages: ), officially the United Mexican States (; EUM ), is a List of sovereign states, country in the southern portion of North America. It is borders of Mexico, bordered to the north by the United States; ...
,
India India (Hindi: ), officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by population, second-most populous country, the List of countries and dependencies by area, seventh-largest ...

India
, and other places, and often carved, polished and sold. This material is much softer than true onyx, and much more readily available. The majority of carved items sold as "onyx" today are this
carbonate In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its natural form as a crystallinity, crystalline min ...
material. Artificial onyx types have also been produced from common chalcedony and plain agates. The first-century naturalist
Pliny the Elder Gaius Plinius Secundus (AD 23/2479), called Pliny the Elder (), was a Roman author, a naturalist Natural history is a domain of inquiry involving organisms, including animals, fungus, fungi, and plants, in their natural environment, leaning ...

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 or
hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the diges ...
to carbonise 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 Nitric acid (), also known as ''aqua fortis'' (Latin for "strong water") and spirit of niter, is a highly corrosive mineral acid. The pure compound is colorless, but older samples tend to acquire a yellow cast due to decomposition into nitrogen ...
have been used to lighten or eliminate undesirable colours.


Geographic occurrence

Onyx is a gemstone found in various regions of the world including Greece, Yemen, Uruguay, Argentina, Australia, Brazil, Canada, China, Czech Republic, Germany, Pakistan, India, Indonesia, Madagascar, Latin America, the UK, and various states in the US.


Historic use

It has a long history of use for hardstone carving and jewelry, where it is usually cut as a cabochon or into beads. It has also been used for intaglio (jewelry), intaglio and hardstone cameo (carving), 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 was used in Egypt as early as the Second Dynasty to make bowls and other pottery items. Use of sardonyx appears in the art of Minoan civilization, Minoan Crete, notably from the archaeological recoveries at Knossos. Brazilian green onyx was often used as plinths for art deco 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 - a brownish color) is mentioned in the Bible as well. Onyx was known to the Ancient Greeks and Ancient Rome, Romans. The first-century naturalist
Pliny the Elder Gaius Plinius Secundus (AD 23/2479), called Pliny the Elder (), was a Roman author, a naturalist Natural history is a domain of inquiry involving organisms, including animals, fungus, fungi, and plants, in their natural environment, leaning ...

Pliny the Elder
described both type of onyx and various artificial treatment techniques in his ''Natural History (Pliny), Naturalis Historia''. Slabs of onyx (from the Atlas Mountains) were famously used by Mies van der Rohe in Villa Tugendhat at Brno (completed 1930) to create a shimmering semi-translucent interior wall. The Hôtel de la Païva in Paris is noted for its yellow onyx décor, and the new Mariinsky Theatre Second Stage in St.Petersburg uses yellow onyx in the lobby.


Superstitions

The ancient Romans entered battle carrying amulets of sardonyx engraved with Mars (mythology), Mars, the god of war. This was believed to bestow courage in battle. In Renaissance Europe, wearing sardonyx was believed to bestow eloquence. A traditional Persians, Persian belief is that it helped with epilepsy. Sardonyx was traditionally used by English midwives to ease childbirth by laying it between the breasts of the mother.Three thousand years of mental healing By George Barton Cutten, 1911 P.202


See also

* *


References


External links

* {{Shades of black Chalcedony Quartz gemstones Shades of black