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Onyx
| Onyx | |
|---|---|
 | |
| General | |
| Category | Chalcedony variety (silicate minerals) |
| Formula (repeating unit) | SiO2 (silicon dioxide) |
| Crystal system | Trigonal |
| Identification | |
| Formula mass | 60.08 g/mol |
| Color | Various |
| Cleavage | None |
| Fracture | Uneven, conchoidal |
| Mohs scale hardness | 6.5–7 |
| Luster | Vitreous, silky |
| Streak | White |
| Diaphaneity | Translucent |
| Specific gravity | 2.55–2.70 |
| Optical properties | Uniaxial/+ |
| Refractive index | 1.530–1.543 |
| References | [1][2] |
Onyx is the parallel-banded variety of chalcedony, a silicate mineral. Agate and 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 of alabaster, marble, calcite, obsidian, and opal, and misleadingly to materials with contorted banding, such as "cave onyx" and "Mexican onyx".[1][3][4]
- ^ a b c "Onyx". Mindat.org. Retrieved 2015-08-22.
- ^ "Onyx". gemdat.org. Retrieved 2015-08-22.
- ^ Manutchehr-Danai, Mohsen (2013). Dictionary of Gems and Gemology. New York: Springer. pp. 340–341. ISBN 9783662042885.
- ^ Schumann, Walter (2009). Gemstones of the World. New York: Sterling. p. 158. ISBN 9781402768293.
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