(1) Onyx is a variety of the microcrystalline quartz, called chalcedony.
(2) Distinctive black or white alternating bands are formed by the deposition of silica in gas cavities in lava.
(1) Onyx got its name from the Greek word for “claw” or “fingernail” because these veins resemble the colors of a fingernail. This is largely in part due to the banding appearance on the stone.
(IS THIS TRUE?) Since ancient Egyptian times, onyx has been stained to improve or change its color. Natural black onyx is rare, so the commercial black variety is usually agate that has been stained by the sugar-sulfuric acid treatment, soaked in sugar and then heated in sulfuric acid to carbonize the sugar.