metamorphic
Biotite-rich schist
Mica schist, chiefly quartz + biotite mica (variable feldspar and garnet)
AI-generated identification · may be incorrectTypically dark brown-black, sparkly, and foliated, with platy mica grains and uneven fracture; hardness about 2.5–3 for biotite and 6–7 for quartz, with a generally silky to vitreous luster. The image suggests a fine- to medium-grained mica-rich metamorphic rock, though mineral identification is limited by the photogra…
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Physical properties
Typically dark brown-black, sparkly, and foliated, with platy mica grains and uneven fracture; hardness about 2.5–3 for biotite and 6–7 for quartz, with a generally silky to vitreous luster. The image suggests a fine- to medium-grained mica-rich metamorphic rock, though mineral identification is limited by the photograph.
Formation & geological history
Forms when shale or other clay-rich sediment is subjected to elevated temperature and pressure during regional metamorphism, commonly during mountain building. Its exact geological age cannot be determined visually; schists occur from Precambrian to recent orogenic belts.
Uses & applications
Used mainly as decorative stone, landscaping material, and teaching or collecting specimens; strong foliation limits many construction uses. Attractive mica-rich pieces have modest collector value.
Geological facts
Visible glitter commonly comes from aligned biotite or muscovite flakes reflecting light. Schistosity—the tendency to split along mica-rich planes—is its defining texture.
Field identification & locations
Look for abundant visible mica, planar foliation, and a sparkly surface; a streak, hardness, and acid test can help distinguish it from dark igneous rocks. Common worldwide in metamorphic mountain belts, including the Appalachians, Alps, and Himalaya.
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