"Phyllite (/ˈfɪlaɪt/ FIL-yte) is a type of foliated metamorphic rock formed from slate that is further metamorphosed so that very fine grained white mica achieves a preferred orientation. It is primarily composed of quartz, sericite mica, and chlorite.
Phyllite has fine-grained mica flakes, whereas slate has extremely fine mica flakes, and schist has large mica flakes, all mica flakes of which have achieved a preferred orientation. Among foliated metamorphic rocks, it represents a gradation in the degree of metamorphism between slate and schist.[citation needed]
The minute crystals of graphite, sericite, or chlorite, or the translucent fine-grained white mica, impart a silky, sometimes golden[citation needed] sheen to the surfaces of cleavage, called "phyllitic luster"." - (en.wikipedia.org 03.09.2023)
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