6.5 - 7.0 on the Mohs scale.

Worldwide. A member of the chalcedony family (micro-crystalline quartz).

Onyx is the name given to chalcedony which is uniform in color, generally black or white. Onyx should not be confused with onyx marble, a banded stone which is a form of limestone (calcite or aragonite).

Black and colored onyx is always dyed.

More information on gemstone enhancements.

Onyx is a member of the Chalcedony gemstone family.