metamorphic
Biotite-rich schist
Mica schist; primarily quartz, feldspar, and biotite mica
AI-generated identification · may be incorrectTypically gray to brown-black, with a glittery vitreous to pearly luster and strongly foliated, flaky texture. Mohs hardness is about 2.5–3 for biotite and 6–7 for quartz; mica has perfect basal cleavage, while the rock splits along foliation.
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Physical properties
Typically gray to brown-black, with a glittery vitreous to pearly luster and strongly foliated, flaky texture. Mohs hardness is about 2.5–3 for biotite and 6–7 for quartz; mica has perfect basal cleavage, while the rock splits along foliation.
Formation & geological history
Formed when shale or other clay-rich sedimentary rock underwent medium-grade regional metamorphism, commonly during mountain building. Its exact age cannot be determined from the photograph; such rocks range from Precambrian to recent geological orogenies.
Uses & applications
Used locally as decorative stone, landscaping material, fill, and occasionally thin facing slabs, but its pronounced foliation limits structural construction use. Attractive mica-rich pieces are collected as teaching or display specimens.
Geological facts
The visible sparkle comes mainly from aligned biotite flakes reflecting light. Schistosity records intense directed pressure and recrystallization deep within a mountain belt.
Field identification & locations
Identify it by abundant visible mica, planar foliation, glittery surfaces, and easy splitting into irregular sheets; unlike slate, its mica crystals are coarse and obvious. Common in metamorphic mountain belts worldwide, including the Appalachians, Alps, and Himalaya.
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