metamorphic
Foliated metamorphic rock, likely biotite schist
Mica schist, chiefly quartz, feldspar, and biotite mica
AI-generated identification · may be incorrectDark gray, medium- to coarse-grained, with abundant reflective mica flakes and weakly visible foliation. Typical hardness is about 2.5–7 depending on the tested mineral; mica has perfect cleavage, while quartz and feldspar are harder and granular.
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Physical properties
Dark gray, medium- to coarse-grained, with abundant reflective mica flakes and weakly visible foliation. Typical hardness is about 2.5–7 depending on the tested mineral; mica has perfect cleavage, while quartz and feldspar are harder and granular.
Formation & geological history
Formed when clay-rich sedimentary rock was subjected to elevated temperature and directed pressure during regional metamorphism, commonly during mountain building. Its exact geological age cannot be determined from the photograph.
Uses & applications
Used locally as decorative stone, landscaping material, and occasionally wall or paving stone; attractive mica-rich pieces are collected, but it is generally not a high-value gemstone.
Geological facts
The glitter comes mainly from aligned mica crystals, which can make schist split along foliation planes. The specimen may instead be a fine-grained gneiss or mica-rich greenschist if its layering is less pronounced than it appears.
Field identification & locations
Common in metamorphic belts worldwide, including the Appalachians, Alps, Himalaya, and Scandinavian mountains. Field identification relies on visible mica sparkle, planar fabric, and separation along foliation; it should not fizz with dilute acid.
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