Meaning of pyroclastic

py•ro•clas•tic

Pronunciation: (pī"ru-klas'tik), [key]
— adj. Geol.
  1. composed chiefly of fragments of volcanic origin, as agglomerate, tuff, and certain other rocks; volcaniclastic.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.