The Collaborative International Dictionary of English v.0.48:

Andesite \An"des*ite\, n. (Min.)
   An eruptive rock allied to trachyte, consisting essentially
   of a triclinic feldspar, with pyroxene, hornblende, or
   hypersthene.
   [1913 Webster]

WordNet (r) 3.0 (2006):

andesite
    n 1: a dark grey volcanic rock