Polytypism of Micas. I. MDO Polytypes and Their Derivation

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

Abstract: A procedure leading to the systematic derivation of all maximum-degree-of-order (MDO) polytypes in the three mica families, based on the order-disorder (OD) interpretation of mica structures, has been developed. There are 6 non-equivalent (8 non-congruent) homo-octahedral, 14 (22) mesooctahedral, and 36 (60) hetero-octahedral MDO mica polytypes. The ideal ditrigonalization of tetrahedral sheets leads to a splitting of the polytypes in any mica family into two subfamilies with octahedral and trigonal prismatic coordination of the interlayer cations, respectively.

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

Clays and Clay Minerals; December 1984 v. 32; no. 6; p. 453-463; DOI: 10.1346/CCMN.1984.0320603
© 1984, The Clay Minerals Society
Clay Minerals Society (www.clays.org)