metamorphic
Biotite schist
Mica schist; chiefly quartz, feldspar, and biotite mica
AI-generated identification · may be incorrectTypically gray to black, strongly foliated, and sparkly with platy mica; biotite has Mohs hardness 2.5–3, quartz 7, and schist has variable density and cleavage along foliation. The specimen shows coarse, flaky crystals and irregular metamorphic banding.
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Physical properties
Typically gray to black, strongly foliated, and sparkly with platy mica; biotite has Mohs hardness 2.5–3, quartz 7, and schist has variable density and cleavage along foliation. The specimen shows coarse, flaky crystals and irregular metamorphic banding.
Formation & geological history
Forms when shale or other clay-rich sediment is subjected to elevated temperature and directed pressure during regional metamorphism, commonly in mountain-building belts. Its exact age cannot be determined from the photograph; schists range from Precambrian to recent geologic settings.
Uses & applications
Used locally as decorative stone, landscaping material, wall stone, and aggregate, though strong foliation limits structural use. Attractive mica-rich pieces are mainly collected as teaching or display specimens.
Geological facts
The glitter comes from aligned mica flakes reflecting light; this alignment produces schistosity. Weathered surfaces may split into thin, flaky layers.
Field identification & locations
Common in metamorphic terranes worldwide, including the Appalachians, New England, Scotland, Norway, and the Alps. Identify it by visible mica sparkle, pronounced foliation, and layers that separate more readily than granite; distinguish it from slate by its coarser crystals.
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