Source : Webster's Revised Unabridged Dictionary (1913)

Aphanite \Aph"a*nite\, n. [Gr. ? invisible; 'a priv. + ? to
   appear.] (Min.)
   A very compact, dark-colored ?ock, consisting of hornblende,
   or pyroxene, and feldspar, but neither of them in perceptible
   grains.

Source : WordNet®

aphanite
     n : fine-grained homogeneous rock (such as basalt) containing
         minerals undetectable by the naked eye