Onyx

Onyx, an agate formed of alternating white and black, or white and dark-brown stripes of chalcedony. More rarely a third colour of stripes occurs. The finest specimens are brought from India. Onyx is in much esteem for ornamental purposes. The ancients valued it very highly, and used it much for cameos. Many of the finest cameos in existence are of onyx. The name onyx, however, appears to have been applied by the ancients more extensively than it now is, and even to striped calcareous alabaster, such as is now called Onyx Marble. The Sardonyx of the ancients is a variety of onyx in which white stripes alternate with stripes of a dark-red variety of carnelian, called sard or sarda. It is one of the rarest and most beautiful kinds of onyx, and is more valued than carnelian.