The word Sardonyx is derived from the Greek, Sard meaning "reddish brown," and onyx meaning "veined gem."

 

Onyx is striped, semiprecious variety of the silica mineral agate with white and black, brown or red alternating bands. Its properties are the same as those of quartz. 

 

The name onyx was used by the Romans for a variety of stones including alabaster, chalcedony, and what is now known as onyx marble. Roman soldiers wore sardonyx talismans engraved with heroes such as Hercules or Mars, god of war. They believed that the stone would make the wearer as brave and daring as the figured carved on it. During the Renaissance, sardonyx was believed to bring eloquence upon the wearer and was regarded with great value by public speakers and orators.

Cameos are cut from stones, such as onyx, sardonix or agate, where different colors occur in layers. The background material is cut away, leaving the cameo design in relief. Onyx is also used in intaglios because its layers can be cut to show a color contrast between the design and the background. 
Sardonyx at one time was more precious than gold, silver, or sapphire. Sardonyx is always widely used in cameos and intaglios.