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Onyx

From Wikipedia, the free encyclopedia
This article is about the mineral. For the New York hip hop group, seeOnyx (hip hop group).For other uses, seeOnyx (disambiguation).
Onyx
Black onyx with concentric white bands
General
CategoryChalcedonyvariety (silicate minerals)
Formula
(repeating unit)		SiO2(silicon dioxide)
Crystal systemTrigonal
Identification
Formula mass60.08 g/mol
ColorVarious
CleavageNone
FractureUneven,conchoidal
Mohs scalehardness6.5–7
LusterVitreous, silky
StreakWhite
DiaphaneityTranslucent
Specific gravity2.55–2.70
Optical propertiesUniaxial/+
Refractive index1.530–1.543
References[1][2]

Onyxis the parallel-banded variety ofchalcedony,asilicate mineral.Agateand onyx are both varieties of layered chalcedony that differ only in the form of the bands. Onyx has parallel bands, while agate has curved bands. The colors of its bands range from black to almost every color. Specimens of onyx commonly contain bands of black or white or both.[1]Onyx, as a descriptive term, has also been applied to parallel-banded varieties ofalabaster,marble,calcite,obsidian,andopal,and misleadingly to materials with contorted banding, such as "cave onyx" and "Mexican onyx".[1][3][4]

Etymology

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Onyxcomes through Latin (of the same spelling), from the Ancient Greekὄνυξ,meaning "claw" or "fingernail". Onyx with pink and white bands can sometimes resemble a fingernail.[5]The English word "nail" iscognatewith the Greek word.

Varieties

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Cabochonsof red onyx, also called sardonyx
A photograph of 6 smooth black pebbles with white markings, arranged in a circle
Black onyx with white streaks

Onyx is formed ofchalcedonybands in alternating colors. It iscryptocrystalline,consisting of fine intergrowths of thesilicamineralsquartzandmoganite.Its bands are parallel, unlike the more chaotic banding that often occurs inagates.[6]

Sardonyxis a variant in which the colored bands aresard(shades of red) rather than black. Black onyx is perhaps the most famous variety, but it is not as common as onyx with colored bands. Artificial treatments have been used since ancient times to produce the black color in "black onyx" and the reds and yellows in sardonyx. Most "black onyx" on the market is artificially colored.[7][8]

Imitations and treatments

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The name has also commonly been used to label other banded materials, such as bandedcalcitefound inMexico,India,and other places, and often carved, polished, and sold. This material is much softer than true onyx and more readily available. The majority of carved items sold as "onyx" today are thiscarbonatematerial.[9][10]

Artificial onyx types have also been produced from common chalcedony and plain agates. The first-century naturalistPliny the Elderdescribed these techniques used in Roman times.[11]Treatments for producing black and other colors include soaking or boiling chalcedony in sugar solutions, then treating withsulfuricorhydrochloric acidto carbonize sugars which had been absorbed into the top layers of the stone.[8][12]These techniques are still used, as well as other dyeing treatments, and most so-called "black onyx" sold is artificially treated.[13]In addition to dye treatments, heating and treatment withnitric acidhave been used to lighten or eliminate undesirable colors.[8]

Geographic occurrence

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Onyx can be 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.[9]

Historical use

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A photograph showing a roughly rectangular gem set in a gold frame with 2 carved panels with various figures carved in shallow from translucent white chalcedony against a solid black background
TheGemma Augusteais a Romancameoproduced 9–12 AD andcarvedin a two-layered onyx gem (19 × 23 cm)

It has a long history of use forhardstone carvingandjewelry,where it is usually cut as acabochonor into beads. It has also been used forintaglioand hardstonecameoengraved gems,where the bands make the image contrast with the ground.[14]Some onyx is natural but much of the material in commerce is produced by the staining of agate.[15]

Onyx was used inEgyptas early as the Second Dynasty to make bowls and other pottery items.[16]Use of sardonyx appears in the art ofMinoanCrete,notably from the archaeological recoveries atKnossos.[17]

Brazilian green onyx was often used as plinths forart decosculptures created in the 1920s and 1930s. The German sculptorFerdinand Preissused Brazilian green onyx for the base on the majority of hischryselephantinesculptures.[18]Green onyx was also used for trays and pin dishes – produced mainly inAustria– often with small bronze animals or figures attached.[19]

Onyx is mentioned in the Bible many times.[20]Sardonyx (onyx in which white layers alternate with sard - a brownish color) is mentioned in the Bible as well.[21]

Onyx was known to theAncient GreeksandRomans.[22]The first-century naturalistPliny the Elderdescribed both types of onyx and various artificial treatment techniques in hisNaturalis Historia.[11]

Slabs of onyx (from theAtlas Mountains) were famously used byMies van der RoheinVilla TugendhatatBrno(completed 1930) to create a shimmering semi-translucent interior wall.[23][24]

TheHôtel de la Païvain Paris is noted for its yellow onyx décor, and the newMariinsky Theatre Second Stagein St.Petersburg uses yellow onyx in the lobby.

Superstitions

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The ancient Romans entered battle carrying amulets of sardonyx engraved withMars,the god of war. This was believed to bestow courage in battle. In Renaissance Europe, wearing sardonyx was believed to bestow eloquence.[25]A traditionalPersianbelief is that it helped withepilepsy.[26]Sardonyx was traditionally used by English midwives to ease childbirth by laying it between the breasts of the mother.[27]

See also

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  • Birthstone– Gemstones representing a person's birth month
  • Chalcedony– Microcrystalline varieties of silica
  • Gemstone– Piece of mineral crystal used to make jewelry
  • Jasper– Chalcedony variety colored by iron oxide
  • List of minerals– List of minerals with Wikipedia articles

References

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  1. ^abcOnyx,Mindat.org,retrieved2015-08-22
  2. ^"Onyx".gemdat.org.Retrieved2015-08-22.
  3. ^Manutchehr-Danai, Mohsen (2013).Dictionary of Gems and Gemology.New York: Springer. pp. 340–341.ISBN9783662042885.
  4. ^Schumann, Walter (2009).Gemstones of the World.New York:Sterling.p. 158.ISBN9781402768293.
  5. ^"Online Etymology Dictionary".etymonline.Retrieved22 August2015.
  6. ^Assaad, Fakhry A.; LaMoreaux, Philip E. Sr. (2004). Hughes, Travis H. (ed.).Field Methods for Geologists and Hydrogeologists.Berlin,Heidelberg,New York:Springer-Verlag.p. 8.ISBN3-540-40882-7.
  7. ^Sinkankas, John (1959).Gemstones of North America.Vol. 1.Princeton, New Jersey:Van Nostrand.p. 316.
  8. ^abc"The Manufacture of Gem Stones".Scientific American.New York: Munn & Company: 49. 25 July 1874.
  9. ^ab"Onyx".mindat.org.Retrieved22 August2015.
  10. ^Hurlbut, Cornelius S.; Sharp, W. Edwin (1998).Dana's Minerals and How to Study Them(4th ed.). New York, New York: Wiley. p.200.ISBN0-471-15677-9.
  11. ^abO'Donoghue, Michael (1997).Synthetic, Imitation, and Treated Gemstones.Boston: Butterworth-Heinemann. pp. 125–127.ISBN0-7506-3173-2.
  12. ^Read, Peter G. (1999).Gemmology.Oxford: Butterworth-Heinemann. p. 160.ISBN0-7506-4411-7.
  13. ^Liddicoat, Richard Thomas (1987).Handbook of Gem Identification(12th ed.). Santa Monica, California: Gemological Institute of America. pp. 158–160.ISBN0-87311-012-9.
  14. ^Kraus, Edward Henry; Slawson, Chester Baker (1947).Gems and Gem Materials.New York, New York: McGraw-Hill. p.227.
  15. ^Liddicoat, Richard Thomas; Copeland, Lawrence L. (1974).The Jewelers' Manual.Los Angeles, California: Gemological Institute of America. p. 87.
  16. ^Porter, Mary Winearls(1907).What Rome was Built with: A Description of the Stones Employed.Rome: H. Frowde. p.108.
  17. ^C. Michael Hogan (2007)Knossos fieldnotes,The Modern Antiquarian
  18. ^"Ferdinand Preiss".Hickmet.Retrieved18 June2015.
  19. ^"Lot 419, Schmidt-Hofer, Otto, 1873-1925 (Germany)".ArtValue.
  20. ^"BibleGateway".biblegateway.Retrieved22 August2015.
  21. ^"BibleGateway".biblegateway.Retrieved22 August2015.
  22. ^Administrator."Onyx".gemstone.org.Retrieved22 August2015.
  23. ^"The Interiors".Villa Tugendhat.Retrieved2 September2017.
  24. ^"Tugendhat Villa in Brno".UNESCO.Retrieved2 September2017.
  25. ^Firefly Guide to Gems By Cally Oldershaw, p.168
  26. ^The Mining World, Volume 32, June 25, 1910, p.1267
  27. ^Three thousand years of mental healing By George Barton Cutten, 1911 P.202
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