metamorphic
Biotite mica schist (mica-rich metamorphic specimen)
Biotite-rich schist; chiefly phlogopite/biotite mica, commonly with quartz and feldspar
AI-generated identification · may be incorrectVery dark brown to black, platy and strongly foliated, with a vitreous to pearly luster and perfect basal cleavage; individual mica flakes are typically Mohs 2.5–3, while quartz inclusions are ~7. Specific gravity is commonly about 2.7–3.1.
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Physical properties
Very dark brown to black, platy and strongly foliated, with a vitreous to pearly luster and perfect basal cleavage; individual mica flakes are typically Mohs 2.5–3, while quartz inclusions are ~7. Specific gravity is commonly about 2.7–3.1.
Formation & geological history
Forms when clay-rich or feldspathic sedimentary rocks undergo regional metamorphism, aligning mica into schistosity under heat and directed pressure; commonly Paleozoic to Precambrian in exposed metamorphic terranes.
Uses & applications
Used locally as decorative stone, aggregate, and sometimes dimension stone, though abundant mica weakens it; attractive specimens are collected, but it is not generally a jewelry gemstone.
Geological facts
The shiny sheets can be peeled into thin elastic flakes and may show reddish-brown or silvery reflections. Mica’s cleavage is so perfect that flakes split into flexible sheets.
Field identification & locations
Identify by its glittering, aligned flakes, pronounced foliation, and easy splitting; common in mountain belts and metamorphic complexes worldwide, including the Appalachians, Canadian Shield, and Alps.
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