Onyx

Onyx is a gemstone whose description can have several connotations. Its most accepted gemstone definition describes a solid black Chalcedony, or a streaked or layered black and white Chalcedony. The term Onyx is occasionally used to described any engraved stone with a solid color base, or it may describe any streaked gemstone with parallel banding. In its solid black form, Onyx is the most traditional black gemstone.

Chemical Formula	SiO2
Color	White, Black, Banded
Hardness	7
Crystal System	Hexagonal
Refractive Index	1.54Â -Â 1.55
SG	2.63Â -Â 2.65
Transparency	Translucent to opaque
Double Refraction	.009
Luster	Vitreous
Cleavage	Indiscernible
Mineral Class	Quartz (Chalcedony)