The Collaborative International Dictionary of English v.0.48:

Talc \Talc\ (t[a^]lk), n. [F. talc; cf. Sp. & It. talco, LL.
   talcus; all fr. Ar. talq.] (Min.)
   A soft mineral of a soapy feel and a greenish, whitish, or
   grayish color, usually occurring in foliated masses. It is
   hydrous silicate of magnesia. Steatite, or soapstone, is
   a compact granular variety.
   [1913 Webster]

   Indurated talc, an impure, slaty talc, with a nearly
      compact texture, and greater hardness than common talc; --
      called also talc slate.
      [1913 Webster] Talcose