metamorphic

Likely biotite-rich metamorphic rock (mica schist or amphibolite)

Mica schist/amphibolite; chiefly biotite mica ± hornblende, plagioclase, quartz

AI-generated identification · may be incorrect

Dark gray-black, coarse and strongly foliated, with reflective platy grains and pale mineral patches. Biotite has Mohs hardness 2.5–3 and perfect basal cleavage; amphibole is harder (5–6), while quartz is ~7. Specific gravity is typically about 2.8–3.3; luster is vitreous to pearly on mica surfaces.

Identified September 12, 2026More metamorphic →

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Physical properties

Formation & geological history

Most consistent with a metamorphic rock formed by pressure, heat, and directed deformation of an igneous or clay-rich protolith during Alpine mountain building. Rocks of this type are common in the Alps, including around 46.8°N, 9.2°E, though a photograph cannot determine its precise age.

Uses & applications

Used locally as crushed stone, aggregate, or decorative stone; attractive foliated pieces are collected, but this specimen is unlikely to have significant gem value.

Geological facts

The glitter comes mainly from aligned mica cleavage surfaces, producing schistosity. A fresh surface may split into thin, shiny flakes.

Field identification & locations

Look for planar foliation, flexible or flaky black-brown mica, and possible nonmagnetic behavior; a streak, hardness, cleavage, and magnet test would help separate schist from amphibolite or gneiss. Common in Alpine metamorphic belts.