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Onyx Stone
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.
