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Onyx




Onyx is a cryptocrystalline form of quartz. The colors of its bands range from white to almost every color (save some shades, such as Purple or Blue.) Commonly, specimens of onyx available contain bands of colors of white, tan, and brown. Sardonyx is a variant in which the colored bands are sard (shades of red) rather than black. Pure black Onyx is common, and perhaps the most famous variety, but not as common as Onyx with banded colors.

  It is usually cut as a cabochon, or into beads, and is also used for intaglios and cameos, where the bands make the image contrast with the ground. Some onyx is natural but much is produced by the staining of agate.

The name has sometimes been used, incorrectly, to label other banded lapidary materials, such as banded calcite found in Mexico, Pakistan, 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 material. [1]

Technical details
Chemical composition and name SiO2 - Silicon dioxide
Hardness (Mohs scale) 7
Specific gravity 2.65 - 2.667
Refractive index (R.I.) 1.543 - 1.552 to 1.545 - 1.554
Birefringence 0.009
Optic sign Positive
Optical character Uniaxial

Additional recommended knowledge

Contents

Culture and historical usage

   

History

Onyx is originally an Assyrian word meaning ring, and so could refer to anything used for making rings.


 

Astrological Relations

The onyx is the stone for the western zodiac sign, Leo, and the Chinese zodiac sign of the Ox. It can be many different colours, but the ones with the reddish brown colour is the preferred type. Onyx is said to banish grief, bring fortune to its possessor, bring recognition of personal strengths and increase regeneration, intuition and instincts. It is also thought to decrease sexual desire and help to change bad habits. [2]

Precautions

Onyx should not be cleaned with an ultrasonic cleaner or cleaned with abrasive or ammonia based cleaner as using such types can cause discolouration of the stone.

References

  • http://www.gemstone.org/gem-by-gem/english/onyx.html
  • http://www.bernardine.com/gemstones/onyx.htm
  • http://www.mindat.org/min-2999.html

See also

Look up onyx in Wiktionary, the free dictionary.
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Onyx". A list of authors is available in Wikipedia.
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