Steatite

From ArchaeoWiki

Steatite (also termed "soapstone") is a soft metamorphic rock, a talc-schist largely composed of the mineral talc and high in magnesium. The name reflects a 'soapy' texture that may be discerned upon handling.

On account of its lack of hardness, talc measuring 1 on the Moh's Scale, steatite represented a popular choice in the Ancient Near East and Egypt as a stone for carving amulets, small objects and small sculpture. Steatite's chemical stability and resistance to acid-based degradation doubtless assisted in this regard. Steatite could be greatly stabilised for everyday use by combining exterior glazing and the addition of other materials with heating so as to vitrify the stone, or create a form of ceramic. When heated to 1000-1200℃, steatite transforms into enstatite or cristalobite, with a corresponding increase in hardness to 5.5-6.5 on the Moh's Scale.