This article is about the mineral. See Onyx (disambiguation) for other meanings

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.

Technical details

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

See also

• list of minerals

de:Onyx