The Collaborative International Dictionary of English v.0.48:

Crusta \Crus"ta\ (kr?s"t?), n. [L., shell, crust, inlaid work.]
   [1913 Webster]
   1. A crust or shell.
      [1913 Webster]

   2. A gem engraved, or a plate embossed in low relief, for
      inlaying a vase or other object.
      [1913 Webster]