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Chemical Formula: SiO2
Mineral Name: Chalcedony
Color: Black, but also found in brown, gray and
white
Hardness: 6.5 - 7.0
Specific Gravity: 2.58-2.64
Onyx
ia a chalcedony that occurs in bands of different
colors. It is composed of relatively straight,
parallel layers of different colors. When the dark
layers are brown or brownish red, it is often called
Sardonyx. Onyx is a form of agate with parallel
banding. This structure lends itself to cameo making.
It is usually cut into 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.
It is available in the regions of USA, Germany,
Brazil, Mexico, India, and Africa.
