Sardonyx,  also known as Sardian Onyx, is a mixture of Onyx and Sard (Carnelian). The word Sardonyx is comes from the Greek, sard meaning “reddish brown,” and onyx meaning “veined gem.” Any colors other than the red and white variety are dyed. 

Sardonyx is the birthstone for August and was more valuable than sapphire at one time.