metamorphic
Likely biotite schist or mica-rich metamorphic rock
Mica schist, predominantly biotite mica with quartz and feldspar
AI-generated identification · may be incorrectDark gray-brown, strongly glittery micaceous surface with visible platy grains and foliation; likely Mohs hardness 2.5–3 for biotite and 6–7 for quartz. Micas show perfect basal cleavage, while the specimen appears irregularly fractured rather than crystalline.
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Physical properties
Dark gray-brown, strongly glittery micaceous surface with visible platy grains and foliation; likely Mohs hardness 2.5–3 for biotite and 6–7 for quartz. Micas show perfect basal cleavage, while the specimen appears irregularly fractured rather than crystalline.
Formation & geological history
Formed when shale or other clay-rich sediment was subjected to elevated heat 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 building facing; thin, flaky pieces have little jewelry value. Attractive, well-foliated specimens may be collected for teaching or display.
Geological facts
The sparkle comes from reflected light on aligned mica flakes, not necessarily metallic ore. Biotite-rich schist commonly weathers into dark, flaky fragments.
Field identification & locations
Identify it by its pronounced layered foliation, flexible or flaky dark mica, and glittery surfaces; distinguish it from gneiss by its finer, more uniformly schistose texture. Common in metamorphic mountain belts worldwide, including the Appalachians, Alps, Scandinavia, and Himalaya.
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