metamorphic
Likely biotite-bearing schist or gneiss
Mica schist/gneiss; chiefly quartz, feldspar, and biotite mica
AI-generated identification · may be incorrectDark gray, coarse-grained, with reflective platy mica and a weakly foliated texture; hardness about 2.5–7 depending on mineral grains, vitreous to pearly luster, and no prominent cleavage as a whole rock.
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Physical properties
Dark gray, coarse-grained, with reflective platy mica and a weakly foliated texture; hardness about 2.5–7 depending on mineral grains, vitreous to pearly luster, and no prominent cleavage as a whole rock.
Formation & geological history
Formed when shale or granitic material was subjected to elevated heat and pressure during regional metamorphism, typically millions to billions of years ago in mountain belts.
Uses & applications
Used locally as decorative stone, landscaping material, wall stone, and aggregate; attractive pieces may be collected, but this rough specimen has little commercial value.
Geological facts
The sparkly surfaces likely reflect aligned biotite or muscovite mica. A precise identification requires testing the flakes and examining a fresh surface or thin section.
Field identification & locations
Common in metamorphic terrains worldwide, including the Appalachian, Canadian Shield, and European mountain regions; look for foliation, mica flakes, and alternating light/dark mineral bands. It may also be a dark granitic rock such as diorite.
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