metamorphic

Biotite schist (mica-rich metamorphic rock)

Schist, chiefly quartz–feldspar–biotite; approximate formulae: biotite K(Mg,Fe)₃AlSi₃O₁₀(F,OH)₂

AI-generated identification · may be incorrect

Typically medium- to coarse-grained with glittering black-brown biotite, pale quartz/feldspar, strong foliation, and mica cleavage. Hardness is about 2.5–3 for biotite and 6–7 for quartz; overall luster is pearly to vitreous, with variable density around 2.7–3.1.

Identified September 16, 2026More metamorphic →

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At a glance

Common name: Biotite schist (mica-rich metamorphic rock)
Scientific name: Schist, chiefly quartz–feldspar–biotite; approximate formulae: biotite K(Mg,Fe)₃AlSi₃O₁₀(F,OH)₂
Category: metamorphic
Identified: September 16, 2026
Method: Standard

AI Estimated Value

Typically $3–$20 for a small common specimen; $20–$75 if unusually fresh, large, or aesthetically foliated.

Not an official valuation

AI estimate for general interest only — not an appraisal. Actual value depends on condition, provenance, and market demand. Verify with a professional before buying, selling, or insuring.

This identification was generated by AI and may contain errors. Verify important details before relying on them — and never use an AI result to judge whether a specimen is safe to handle. Read the full disclaimer

Physical properties

Formation & geological history

Formed when shale or other clay-rich sediment undergoes medium-grade regional metamorphism, commonly during mountain building; ages vary widely from Precambrian to younger orogenic belts.

Uses & applications

Used locally as decorative stone, landscape rock, fill, and occasionally dimension stone, but its foliation limits structural use; attractive pieces are collected as teaching or display specimens.

Geological facts

The specimen’s layered, sparkly texture and dark mica-rich patches are characteristic of schist rather than granite. Rusty brown areas likely reflect weathering of iron-bearing biotite.

Field identification & locations

Identify it by visible aligned mica flakes that split into thin sheets, irregular foliation, and contrasting light quartz/feldspar bands; common in metamorphic mountain belts worldwide, including New England, the Appalachians, the Alps, and the Himalaya.