Phyllites are fine-grained metamorphic rocks with well developed foliation, or alignment of platy or elongate grains. Phyllites typically consist of micas, quartz, and sodic plagioclase, formed during recrystallization of shales during regional dynamothermal metamorphism.
The photo (crossed polarizers) shows strongly aligned, brightly colored muscovite, darker biotite, and light gray quartz and feldspars.
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