metamorphic
Dark mica-rich metamorphic rock, likely schist
Mica schist, probably biotite–muscovite schist; exact identification requires testing
AI-generated identification · may be incorrectFine to medium-grained, very dark gray-purple surface with sparkly mica reflections and weak foliation. Mica schist typically has Mohs hardness 2–3 on cleavage surfaces, vitreous to pearly luster, and visible platy crystals; cleavage is strong along mica layers.
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Physical properties
Fine to medium-grained, very dark gray-purple surface with sparkly mica reflections and weak foliation. Mica schist typically has Mohs hardness 2–3 on cleavage surfaces, vitreous to pearly luster, and visible platy crystals; cleavage is strong along mica layers.
Formation & geological history
Formed when clay-rich sedimentary rock was subjected to elevated pressure and temperature during regional metamorphism, commonly during mountain building. Ages vary widely, from Precambrian to Phanerozoic.
Uses & applications
Used locally as decorative facing stone, landscaping material, and aggregate, though mica-rich varieties split and weather easily; attractive pieces may be collected or polished.
Geological facts
The glitter is likely reflected light from aligned mica flakes rather than metallic mineralization. Purple coloration may reflect lighting, iron-bearing mica, or minor accessory minerals.
Field identification & locations
Look for thin, parallel layers, glittering flexible flakes, and splitting along foliation; a glass scratch test and close inspection of mica plates help distinguish it from basalt. Common in metamorphic belts worldwide, including the Appalachians, Alps, and Himalaya.
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