A person who breaks crystals in order to study them.
Mid 19th century; earliest use found in William Whewell (1794–1866), college head and writer on the history and philosophy of science. From crystallo- + -clast, after French cristalloclaste (J. B. L. de Romé de l'IsleCristallographie (ed. 2, 1783) I Pref. p. xxvii: see note at definition).