Chalcedony

Chalcedony was a mixture of quartz and moganite, usually white, but rare variations included gray or black.

Description
This semi-precious stone was the base mineral in many gem-quality stones such as carnelians, chrysoprase, and agates. It was usually cut cabochon and used in making devices that offered protection from the undead. A typical stone had a base value of 50 gp.