What is a Sardonyx (in terms of gems)?

Onyx is a banded variety of chalcedony, a cryptocrystalline form of quartz. The colors of its bands are white and black. SARDONYX is a variant in which the colored bands are sard (shades of red) rather than black

wikipedia.com

Sardonyx is a cryptocrystaline form of quartz (like agate and chalcedony for example) It in fact a form of agate in which the banding is in black (also brown) and white. It is cut with the colour banding parallel to the face of the stone. This results in a stone that when engraved shows the black colour through a white background or the other way round on rare occasions. It is used for signet rings and seal stones.

It's a very bitter, cynical gem.

I believe it is a member of the quartz family.

Never heard of it.. but here is a link to a picture of one!!! Very Pretty!

http://www.wehug.com/sardonyx.html