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CLEAVAGE
Cleavage is a planar deformation fabric, formed under relatively low
temperature metamorphic to non-metamorphic conditions (<350°C), that
imparts on the rock a tendency to split along planes. The term cleavage is
not used for planar fabrics in coarse-grained schist or in gneiss. Foliation is any type of planar fabric in rock, including bedding,
cleavage, schistosity. Foliations are penetrative (occur throughout) in
samples at 10's of cm scale. But Cleavage is a secondary fabric element
(not bedding) formed under low grade metamorphic conditions (or less) that allows the rock to split along planes under tectonic forces.
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