metamorphic
Mica-rich schist
Muscovite–biotite schist, commonly quartz-bearing
AI-generated identification · may be incorrectTypically Mohs 2–3 for mica and about 7 for quartz; silvery-bronze to dark brown, with pearly to vitreous luster. Platy mica produces strong foliation and splits into thin flakes; quartz occurs as granular, harder patches.
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Physical properties
Typically Mohs 2–3 for mica and about 7 for quartz; silvery-bronze to dark brown, with pearly to vitreous luster. Platy mica produces strong foliation and splits into thin flakes; quartz occurs as granular, harder patches.
Formation & geological history
Formed when shale or clay-rich sedimentary rock underwent moderate-to-high-grade regional metamorphism, realigning mica minerals into foliation. Such rocks commonly formed during ancient mountain-building events, often hundreds of millions to billions of years ago.
Uses & applications
Used locally as decorative stone, landscaping material, and occasionally dimension stone, though its pronounced foliation makes it unsuitable for many structural applications. Attractive mica-rich pieces are collected as mineral specimens.
Geological facts
The sparkling appearance comes from reflected light on numerous mica cleavage surfaces rather than metallic metal. Biotite gives dark brown-black tones, while muscovite produces silvery flashes.
Field identification & locations
Identify it by abundant glittering, flexible flakes and a layered texture; quartz-rich areas resist scratching by a steel blade, while mica flakes easily peel. Common in metamorphic belts worldwide, including the Appalachians, New England, Scandinavia, and India.
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