metamorphic
Biotite-rich schist (probable)
Mica schist; chiefly quartz (SiO₂), biotite mica, and feldspar
AI-generated identification · may be incorrectDark, sparkly, foliated matrix with platy mica; typically Mohs 2.5–3 for biotite and 6–7 for quartz, vitreous to pearly luster, and schistose cleavage. The embedded rounded dark fragment may be a separate inclusion or weathered rock clast.
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Physical properties
Dark, sparkly, foliated matrix with platy mica; typically Mohs 2.5–3 for biotite and 6–7 for quartz, vitreous to pearly luster, and schistose cleavage. The embedded rounded dark fragment may be a separate inclusion or weathered rock clast.
Formation & geological history
Forms when clay-rich sedimentary rock undergoes medium-grade regional metamorphism, recrystallizing into aligned mica and quartz; commonly Paleozoic to Precambrian in exposed mountain belts. Exact age cannot be determined from the image.
Uses & applications
Used locally as decorative stone, landscaping material, and occasionally building veneer, but its foliation limits structural use. Attractive mica-rich pieces are collected as specimens rather than used in jewelry.
Geological facts
The glitter comes from reflected mica cleavage surfaces, not necessarily metallic minerals. Schist commonly splits along foliation into thin, irregular plates.
Field identification & locations
Identify it by pronounced layered foliation, abundant glittering flakes, and easy splitting; a hand lens and streak/cleavage tests help distinguish mica from sulfides. Common in the Appalachians, New England, Scotland, Scandinavia, and many metamorphic mountain belts.
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