metamorphic
Likely biotite-rich schist
Mica schist, composed chiefly of quartz and biotite mica
AI-generated identification · may be incorrectDark gray, coarse and visibly flaky with a slight sheen and strong foliation; individual minerals are typically Mohs 2–7 (biotite ~2.5–3, quartz 7). The image alone does not establish exact composition or hardness.
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Physical properties
Dark gray, coarse and visibly flaky with a slight sheen and strong foliation; individual minerals are typically Mohs 2–7 (biotite ~2.5–3, quartz 7). The image alone does not establish exact composition or hardness.
Formation & geological history
Forms when clay-rich sedimentary rock is metamorphosed under heat and pressure, aligning mica into layers. Its age depends on the source locality and cannot be determined from the photo.
Uses & applications
Mostly used as a decorative or educational specimen; some schists are used as facing stone or aggregate, though pronounced foliation can make them split or weather easily.
Geological facts
The layered, glittering texture is called schistosity and results from aligned platy minerals.
Field identification & locations
Look for thin, sparkly mica flakes and a tendency to split along foliation; commonly occurs in regional metamorphic belts. Confirm identification with close inspection or mineral testing, since several dark foliated rocks look similar.
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