Formation of Laths in Fine-Grained Micas and Its Relationship to Stacking Mechanism

N. Güven
Department of Geosciences, Texas Tech. University, P.O. Box 4109, Lubbock, Texas 79409, U.S.A.

Summary: Transmission electron images of fine-grained micas from various clay deposits exhibit lath-shaped units arranged in modes similar to the stacking of layers in different mica polymorphs. Micas in a Georgia bentonite display two sets of parallel laths intersecting at an angle of 120°. Selected area electron diffraction (SAD) of these micas gives a sharp spot pattern indicating a perfect registry between the lattices of individual laths. Furthermore, the SAD pattern has an intensity distribution similar to that of a 2M1 dioctahedral mica. Another mica in an India bentonite shows one set of parallel laths with an intensity distribution expected from a IM biotite. Some of the micas in the Marblehead illite exhibit three sets of parallel laths in a trigonal arrangement similar to the stacking in 3T mica.

Mineralogical Magazine; September 1974 v. 39; no. 307; p. 788-792; DOI: 10.1180/minmag.1974.039.307.05
© 1974, The Mineralogical Society
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