Phyllite

    Phyllite is a type of foliated metamorphic rock primarily composed of quartz, sericite mica, and chlorite; the rock represents a gradiation in the degree of metamorphism between slate and mica schist. Minute crystals of graphite, sericite, or chlorite impart a silky, sometimes golden sheen to the surfaces of cleavage (or schistosity).

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Its constituent platy minerals are larger than those in slate but are not visible with the naked eye.

Phyllites are said to have a "phyllitic texture" and are usually classified as having a low grade on the Barrovian Sequence.

They are regional metamorphic.

The protolith (or parent rock) for a phyllite is a slate.It is very delicate, and can be broken into small sheets.

Phyllite will form under low grade metamorphic conditions. Phyllites are usually black or dark gray. The foliation is commonly crinkled or wavy in appearance.