metamorphic
Biotite schist
Mica schist; chiefly quartz, feldspar, and biotite mica
AI-generated identification · may be incorrectTypically gray to silver-black, with a sparkly micaceous sheen and pronounced foliation; biotite flakes split into thin sheets. Hardness is about 2.5–3 for biotite and 6–7 for quartz; cleavage is excellent in mica, and specific gravity is roughly 2.7–3.0.
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Physical properties
Typically gray to silver-black, with a sparkly micaceous sheen and pronounced foliation; biotite flakes split into thin sheets. Hardness is about 2.5–3 for biotite and 6–7 for quartz; cleavage is excellent in mica, and specific gravity is roughly 2.7–3.0.
Formation & geological history
Formed when shale or another clay-rich sedimentary rock underwent medium-grade regional metamorphism, causing minerals to recrystallize and align under pressure. Commonly Paleozoic to Precambrian in metamorphic belts.
Uses & applications
Used locally as decorative stone, landscaping aggregate, and occasionally building veneer; strongly foliated material is generally unsuitable for heavy construction. Attractive specimens are collected for their glittering mica texture.
Geological facts
The visible silvery sparkle comes from aligned mica grains, while rusty patches likely represent weathered iron-bearing minerals. The image could also represent a closely related quartz-mica schist or foliated gneiss.
Field identification & locations
Look for planar layers, glittering flakes, and easy splitting along foliation; a glassy quartz component distinguishes it from slate. Common in mountain belts and exposed metamorphic terrains worldwide, including the Appalachians and New England.
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