Schists are coarse-grained metamorphic rocks with strong foliation or parallelism of minerals of platy or prismatic habit, such as the micas or amphiboles, developed by tectonic pressures.
The photos above (under crossed polarizers) are of garnet schists; on the left, extinct garnet is surrounded by strongly aligned muscovite and biotite; on the right, extinct garnet is surrounded by white mica and glaucophane.
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