Gray, fine to medium-grained “Berea grit”.
Hematite-cemented quartz; orthoquartzite.
Typical green-gray, fissile, clay-rich.
Brownish gray, kerogen-rich; commercial oil source.
Well-cemented, medium-grained orthoquartzite.
Black, soft; most widely mined.
Cemented glacial gravel.
Small, rounded pebbles and tightly cemented granules.
White, mature, friable.
Dark, waxy, bitumin-rich.
Without Glued-On Grains That Wear Off, Chart Stands up to Repeated use.
