Steatite

Steatite is a mineral, a soft grey schistos stone (silicate of magnesium) resembling but not as soft as soapstone.  It has been a medium for carving for thousands of years. 

Steatite also denotes a glassy ceramic material made from soapstone, used by ancient civilizations to make beads, amulets and seals.  To make the ceramic-like material, steatite was sometimes mixed with additives, it was either carved or molded into the desired shape, and was then heated to a temperature between 1000 and 1200 C.  At that temperature steatite will vitrify, fusing into the glassy substances enstatite and cristobalite.  On the Mohs scale, the change increases hardness from 1 to between 5.5 and 6.5.