These are natural compounds of magnesia and silica, they are generally worked immediately on being raised, being then much softer, but with the evaporation of their moisture they assume the general hardness of marble. The serpentine and steatite are found abundantly in Cornwall; serpentine is often called green marble, and by the Italians Verde de prato, it is much used, but some of the serpentines will not polish well.
Potstone is an inferior variety of serpentine; in Germany it is abundantly turned into various domestic articles in common use, whence its name.
Steatite is called soapstone from its smooth unctuous feel, and when first raised may be scratched with the finger-nail, but it becomes nearly as hard as the others. A variety of steatite is carved by the Chinese into images employed as household gods, and is named figure-stone; until lately, it was supposed to be a preparation of rice. Steatite enters into the composition of porcelain.