|
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.
thumb
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]
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
|
|
ONYX TICKETS
|
Etymology
Onyx
comes through Latin from the Greek onyx
meaning 'claw' or 'fingernail'. With its fleshtone color, onyx can be said to resemble a fingernail. The English word 'nail' is cognate with the Greek word. [2]
Historical usage
thumb.
thumb.
Onyx was known to the ancient Greeks and Romans. [3] Use of sardonyx appears in the art of Minoan Crete, notably from the archaeological recoveries at Knossos. [4] Onyx was used in Egypt as early as the Second Dynasty to make bowls and other pottery items. [5]
thumb
References
- Profile of onyx
- http://www.etymonline.com/index.php?term=onyx
- International Colored Gemstone Association: Onyx
- C. Michael Hogan (2007) ''Knossos fieldnotes'', The Modern Antiquarian
- Mary Winearls Porter, ''What Rome was Built with: A Description of the Stones Employed'', 1907, H. Frowde, Rome, 108 pages
All Wikipedia content is licensed under the GNU Free Document License or is otherwise used here in compliance with the Copyright Act
|