Sardonyx is a semi-precious stone that is formed by two layers, a red-brown layer of sard and a gray, white, black or brown layer of onyx. Sardonyx is a type of quartz.

14th century) A variety of onyx which contains layers of clear red or reddish-brown carnelian alternating with layers of white chalcedony.

Sardonyx is a banded variety of chalcedony characterized by parallel bands of brownish red sard and white translucent onyx. Often cut en cabochon, it is also used for intaglios and cameos. While sardonyx is found naturally in bands of brown, brownish-red and white, much of that found on the market today is actually dyed agate.

A variety of onyx consisting of alternating layers of sard and white chalcedony.