Biotite Schist

Physical Properties

Hardness: 2.5-3.0 on Mohs scale; Color: Black, dark brown, or dark green with silvery highlights; Luster: Vitreous to pearly; Crystal Structure: Monoclinic with perfect basal cleavage; Specific Gravity: 2.8-3.4

Formation & Geological History

Formed through regional metamorphism of clay-rich sedimentary rocks (like shale) under high pressure and temperature. This process aligns the mica crystals into a foliated, sheet-like texture known as schistosity.

Uses & Applications

Used primarily as an insulating material in electrical components due to its heat resistance. Smaller ground-up versions are used in paints, joint compounds, and as a filler in rubber and plastics.

Geological Facts

Biotite is often called 'Black Mica.' The individual sheets are flexible but break easily. It is one of the most common silicate minerals found in the Earth's crust.

Field Identification & Locations

Identify by its sparkly, 'glittery' appearance and its tendency to flake off into thin, flexible sheets with a fingernail. Commonly found in mountain ranges and metamorphic terrains.

Identified on: 4/20/2026

Mode: Standard