Polytypism of Micas. II. Classification and Abundance of MDO Polytypes

S. Ďurovič, Z. Weiss and K.-O. Backhaus
Institute of Inorganic Chemistry, Centre of Chemical Research Slovak Academy of Sciences, 842 36 Bratislava, Czechoslovakia
Coal Research Institute, 716 07 Ostrava-Radvanice, Czechoslovakia
Central Institute of Physical Chemistry, Academy of Sciences of the German Democratic Republic 1199 Berlin-Adlershof, Rudower Chaussee 5, German Democratic Republic

Abstract: The maximum-degree-of-order (MDO) polytypes in all three mica families have been classified into two subfamilies and five homomorphous MDO groups according to their superposition structure and the YZ projection of their structure, respectively. This classification, which is closely related to the diffraction pattern of micas, can be derived directly from the fully descriptive polytype symbols and facilitates the calculation of the identification diagrams as well as the recognition of the relations of homomorphy between the three mica families. All mica structures refined so far by the least-squares method according to the present standards, are those of MDO polytypes.

Key Words: Classification • Homomorphy • Maximum degree of order • Mica • Order-disorder • Polytype

Clays and Clay Minerals; December 1984 v. 32; no. 6; p. 464-474; DOI: 10.1346/CCMN.1984.0320604
© 1984, The Clay Minerals Society
Clay Minerals Society (www.clays.org)