Sardonyx n. : A variety of onyx consisting of sard and white chalcedony in alternate layers.

Example:
What is a Sardonyx (in terms of gems)?

Taxonomy
black onyx, colors, Sardonyx, free encyclopedia, specimens, agate, shades of red, fingernail, Rome, Mineral Gemstones, Quartz, search, purple, colored bands, Etymology, Greek word, Precious metal, metal alloys.

Defination from the web:
Sardonyx) Jump to: navigation, search. This article is about ... Sardonyx is a variant in which the colored bands are sard (shades of red) rather than black. ... Sardonyx (banded agate). The specimen is 2.5 cm (1 inch) wide. ...