Abstract

Microscopic features associated with cleavage in micaceous sandstone, siltstone, and silly slate include mica films, mica beards, homogeneous distribution of oriented mica, and equant or inequant quartz. These features occur in rocks in a wide variety of combinations. In experiments, somewhat similar microstructures are obtained by slow folding of wet, salt-mica specimens. Points of resemblance between the artificial cleavage and natural examples are the presence of mica films, the axial-plane orientation of the cleavage, convergent and divergent cleavage fans, refraction of cleavage across lithological boundaries, evidence of possible solution effects, and total strains that are broadly similar in magnitude and orientation to strains estimated in rocks with slaty cleavage.

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