potstone

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A variety of steatite once used to make cooking vessels.

Century Dictionary and Cyclopedia

1. n. A concretion or mass of flint, of a pear-shaped form, and having a central cavity passing through the longer axis. These concretions occur in the chalk, singly or in vertical rows like columns, at irregular distances from each other, but usually from 20 to 30 feet apart. They were formerly particularly conspicuous near Horstead, about six miles from Norwich, England, in a quarry, now closed, where they were mostly pear-shaped, and about 3 feet in height and 1 foot in diameter. Their origin is not easily explained.
2. n. Same as soapstone or steatite.

Wiktionary

1. n. mineralogy A variety of steatite sometimes manufactured into culinary vessels.

GNU Webster's 1913

1. n. (Min.) A variety of steatite sometimes manufactured into culinary vessels.