This rock contains a high proportion of mica, together with quartz and feldspar. It is especially rich in biotite mica, which gives it a darkish coloring. Compositionally, biotite schist is very similar to the pelitic sediments from which it developed during metamorphism.

TEXTURE A medium-grained rock with crystals that are visible to the naked eye. Biotite schist is, however, best studied with a hand lens. This specimen shows the dark flakes of mica aligned with the foliation.

ORIGIN Forms during medium-grade regional metamorphism of pelitic sediments and other rocks, but these may not become foliated.

Group: METAMORPHIC

Grain size: Medium

Classification: Regional

Pressure: Moderate

Temperature: Low to moderate

Structure: Foliated