The Collaborative International Dictionary of English v.0.48:

Microlite \Mi"cro*lite\, n. [Micro- + -lite.] (Min.)
   [1913 Webster]
   1. A rare mineral of resinous luster and high specific
      gravity. It is a tantalate of calcium, and occurs in
      octahedral crystals usually very minute.
      [1913 Webster]

   2. (Min.) A minute inclosed crystal, often observed when
      minerals or rocks are examined in thin sections under the
      microscope.
      [1913 Webster]