Source : Webster's Revised Unabridged Dictionary (1913)

Peridotite \Per"i*do*tite\, n. [Cf. F. p['e]ridotite.] (Min.)
   An eruptive rock characterized by the presence of chrysolite
   (peridot). It also usually contains pyroxene, enstatite,
   chromite, etc. It is often altered to serpentine.

   Note: The chief diamond deposits in South Africa occur in a
         more or less altered peridotite.

Source : WordNet®

peridotite
     n : a dark coarse-grained igneous rock consisting principally of
         olivine