metamorphic
Biotite-rich mica schist
Mica schist, dominated by biotite mica (K(Mg,Fe)₃AlSi₃O₁₀(F,OH)₂), with probable quartz and feldspar
AI-generated identification · may be incorrectTypically dark brown to black, sparkly, and foliated with platy mica layers; biotite has Mohs hardness 2.5–3, vitreous to pearly luster, perfect basal cleavage, and a sheet-like crystal structure. The specimen’s granular, reflective surface is consistent with mica schist, though the photo is not sufficient for precise…
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Physical properties
Typically dark brown to black, sparkly, and foliated with platy mica layers; biotite has Mohs hardness 2.5–3, vitreous to pearly luster, perfect basal cleavage, and a sheet-like crystal structure. The specimen’s granular, reflective surface is consistent with mica schist, though the photo is not sufficient for precise mineral identification.
Formation & geological history
Forms when shale or other clay-rich sediment undergoes regional metamorphism at moderate temperature and pressure, commonly during mountain building. Its age depends on locality and may range from hundreds of millions to billions of years.
Uses & applications
Used locally as decorative stone, landscaping material, and sometimes dimension stone, but its strong foliation limits structural use. Attractive pieces are collected for their glittering mica texture.
Geological facts
The shimmering flakes are usually biotite rather than precious metal. Schistosity develops as mica crystals align perpendicular to directed pressure.
Field identification & locations
Look for visible aligned mica flakes, easy splitting along foliation, and a dark glittery surface; a streak, hardness, and thin-section test can confirm composition. Common in metamorphic belts worldwide, including the Appalachians, Alps, and Precambrian shields.
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