From Online Dictionary of Crystallography
Revision as of 07:38, 28 April 2006 by MassimoNespolo
An element or compound is polytypic if it occurs in several structural modifications, each of which can be regarded as built up by stacking layers of (nearly) identical structure and composition, and if the modifications differ only in their stacking sequence. Polytypism is a special case of polymorphism: the two-dimensional translations within the layers are essentially preserved.
Chapter 9.2 of International Tables of Crystallography, Volume C