metamorphic
Biotite-bearing metamorphic rock, likely schist
Mica schist; quartz–feldspar–biotite assemblage
AI-generated identification · may be incorrectDark gray-green, coarse and sparkly with visible mica; likely Mohs 2.5–3 for biotite and 6–7 for quartz, with moderate density and micaceous foliation. Uneven fracture and planar splitting may be present, though the specimen appears weathered.
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Physical properties
Dark gray-green, coarse and sparkly with visible mica; likely Mohs 2.5–3 for biotite and 6–7 for quartz, with moderate density and micaceous foliation. Uneven fracture and planar splitting may be present, though the specimen appears weathered.
Formation & geological history
Formed when shale or mudstone was subjected to elevated pressure and temperature 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 dimension stone; attractive mica-rich pieces are collected but are generally not gemstone-grade.
Geological facts
The glitter comes mainly from aligned mica flakes reflecting light. Weathering can produce olive-brown iron-rich surfaces and obscure the rock’s foliation.
Field identification & locations
Common in metamorphic belts worldwide, including the Appalachians, Canadian Shield, Alps, and New England. Confirm with visible foliation, abundant platy mica, and a hardness contrast between scratchable mica and harder quartz grains.
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