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Onyx is a banded variety of chalcedony, a cryptocrystalline form of quartz. The colours of its bands are white and black. It is usually cut as a cabochon, or into beads, and is also used for intaglios and cameos. Some onyx is natural but much is produced by the staining of agate.
| Chemical composition and name | SiO2 - Silicon dioxide |
| Hardness (Mohs scale) | 7 |
| Specific gravity | 2.65 - 2.66 |
| Refractive index (R.I.) | 1.543 - 1.552 to 1.545 - 1.554 |
| Birefringence | 0.009 |
| Optic sign | Positive |
| Optical character | Uniaxial |
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| View Live Article | This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License | |
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