Clay slate; argillaceous schist.

a light or dark-colored metamorphic rock similar to slate but more coarsely-grained and more metamorphosed. It is thinly layered with lustrous cleavage planes (from tiny pieces of mica).

metamorphic rock that is intermediate in grade between slate and mica schist. Small crystals of micas give a silky sheen to the cleavage surfaces.

A fine-grained metamorphic rock with a foliation caused by the preferred orientation of very fine-grained mica.

A metamorphosed mudstone with a silky sheen.

A fine-grained, foliated metamorphic rock intermediate between mica schist and slate; not as tough as slate. Mica crystals give a silky sheen to the cleavage surface.

Silvery, gray to dark-gray, fine- to very fine-grained, schist-like metamorphic rock.

a clay bearing rock with a silky sheen that has been subjected to a low grade of metamorphism.

Fine grained metamorphic rock with well developed cleavage, derived from shale.

foliated metamorphic rock that develops from slate and is marked by a silky sheen and medium grain size.

A very fine-grained, foliated metamorphic rock, generally derived from shale or fine-grained sandstone. Phyllites are usually black or dark gray; the foliation is commonly crinkled or wavy. Differs from less recrystallized slate by its sheen, which is produced by barely visible flakes of muscovite ( mica).

a metamorphic rock intermediate between slate and mica schist. It has a silky sheen on undulating cleavage surfaces.

Fine-grained low-grade metasedimentary rock intermediate in metamorphic-grade between a slate and a schist.

a metamorphosed rock formed from silstones and mudstones in which surfaces exhibit a lustrous sheen caused by newly formed small crystals of mica and chlorite

When a clay is metamorphosed by heat and pressure beyond the stage of a slate, it forms phyllite. The surfaces becomes 'silky' and rather than splitting along parallel planes, it splits into 'leaf' shaped lenses. (Phyllos is Greek for 'leaf'.)

A general term for minerals with a layered crystal structure; also a metamorphosed rock, intermediate in grade between slate and mica schist.

Contains platy minerals too small to be clearly identifiable, distinguished by a glossy sheen.

a low-grade metamorphic rock, intermediate between shale and schist and consisting chiefly of mica or chlorite. [AHDOS

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).