Biotite Mica

Physical Properties

Hardness: 2.5-3.0 Mohs; Color: Dark brown, black, or dark green; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect basal cleavage (easily splits into thin sheets).

Formation & Geological History

Formed in a wide range of igneous and metamorphic conditions. It is common in granites, schists, and gneisses. Geological age varies based on the host rock formation.

Uses & Applications

Used in the electronics industry as an insulator, in paints as a filler, and by collectors for mineral specimens.

Geological Facts

Biotite is known as 'black mica' and is part of a solid-solution series between phlogopite and annite. It was named in honor of Jean-Baptiste Biot, a French physicist.

Field Identification & Locations

Identify by its dark color and the way it flakes into flexible, elastic thin sheets. It is very common worldwide in regions with continental crust.

Identified on: 5/7/2026

Mode: Standard