metamorphic
Biotite schist (probable mica schist)
Mica schist; chiefly quartz, biotite mica, and feldspar
AI-generated identification · may be incorrectGray-brown, strongly foliated, flaky texture with reflective mica; crystals are mostly fine to medium grained. Hardness is about 2.5–3 for biotite and 6–7 for quartz, with excellent mica cleavage and moderate specific gravity (~2.7–3.0).
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Physical properties
Gray-brown, strongly foliated, flaky texture with reflective mica; crystals are mostly fine to medium grained. Hardness is about 2.5–3 for biotite and 6–7 for quartz, with excellent mica cleavage and moderate specific gravity (~2.7–3.0).
Formation & geological history
Formed when shale or other clay-rich sediment was subjected to regional metamorphism, producing aligned mica and visible schistosity. It commonly formed during ancient mountain-building events, though the specimen’s exact age cannot be determined from the image.
Uses & applications
Used locally as decorative stone, landscaping material, and sometimes dimension stone, but its tendency to split limits construction use. Attractive mica-rich pieces are collected as geological specimens.
Geological facts
The glittering flakes are likely biotite, whose perfect basal cleavage lets it separate into thin sheets. Weathering commonly produces rusty staining as iron-bearing biotite oxidizes.
Field identification & locations
Look for a planar, glittery foliation, abundant platy mica, and layers that split readily; a streak or hardness test can distinguish it from slate or phyllite. Common in metamorphic mountain belts worldwide, including the Appalachians, Alps, and Rockies.
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