The Collaborative International Dictionary of English v.0.48:

Potstone \Pot"stone`\, n. (Min.)
   A variety of steatite sometimes manufactured into culinary
   vessels.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Steatite \Ste"a*tite\ (-t[imac]t), n. [Gr. ste`ar, ste`atos,
   fat, tallow: cf. F. st['e]atite.] (Min.)
   A massive variety of talc, of a grayish green or brown color.
   It forms extensive beds, and is quarried for fireplaces and
   for coarse utensils. Called also potstone, lard stone,
   and soapstone.
   [1913 Webster]