mineral

Likely biotite mica

Biotite, a dark mica-group mineral; approximate formula K(Mg,Fe)₃AlSi₃O₁₀(F,OH)₂

AI-generated identification · may be incorrect

Dark brown to black with shiny, platy sheets and perfect basal cleavage; Mohs hardness 2.5–3, monoclinic crystal structure, and specific gravity about 2.7–3.3. The small specimen’s appearance is consistent with mica, though a photo cannot confirm the exact species.

Identified October 1, 2026More mineral →

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Physical properties

Formation & geological history

Forms during crystallization of igneous rocks and metamorphism, commonly in granite, schist, and gneiss; specimens may be of many geological ages.

Uses & applications

Used chiefly as a geological indicator and collectible; ground mica has industrial uses in fillers, paints, and insulation.

Geological facts

Mica splits into thin, flexible sheets because its crystal structure consists of weakly bonded layers.

Field identification & locations

Look for reflective, peelable flakes and sheet-like cleavage in granites and metamorphic rocks; distinguish biotite from lighter-colored muscovite by its dark color.