The Collaborative International Dictionary of English v.0.48:

Muscovite \Mus"co*vite\, n. [See Muscovy glass.]
   1. A native or inhabitant of Muscovy or ancient Russia;
      hence, a Russian.
      [1913 Webster]

   2. An inhabitant of Moscow.
      [PJC]

   3. (Min.) Common potash mica, essentially KAl3Si3O10(OH)2.
      It is used as an electrical insulator. See Mica.
      [1913 Webster]