Phyllite is a low- to intermediate-grade, foliated metamorphic rock. It forms by the metamorphism of slate. Phyllite is typically light gray to dark gray to blackish in color. It has a slightly shiny luster in the light, with slightly wrinkled or crinkled foliation planes. It is principally composed of microcrystalline mica.
Phyllite (4.5 cm across)