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Hematite-cemented quartz; orthoquartzite.

Foliated biotite, coarse, silvery gray with quartz-feldspar bands.

Typical green-gray, fissile, clay-rich.

Brownish gray, kerogen-rich; commercial oil source.

Slaty cleavage; contains hematite.

Chlorite-mica with perfect slaty cleavage.

White, very dark green, and very dark red to light red granoblastic intergrowth of wollastonite, diopside, and andradite.

Gray, fine, friable, with abundant small sanidine crystal fragments.

Massive, chlorite-rich.

Well-cemented, medium-grained orthoquartzite.

Chlorite-bearing.

Dark, coarse-grained, and composed chiefly of hornblende.

Gray andesite with phenocrysts of felspar and/or hornblende.

Classic, dark; from the Columbia Plateau.

Lustrous, black 'hard coal'.

Black, soft; most widely mined.