metamorphic
Biotite schist with quartz–feldspar-rich inclusion
Mica schist, primarily biotite mica (黒雲母) with quartz and feldspar
AI-generated identification · may be incorrectTypically medium- to coarse-grained, strongly foliated, and sparkly from aligned biotite; hardness about 2.5–3 for biotite and 6–7 for quartz, with vitreous quartz luster and perfect mica cleavage. The tan central fragment appears to be a weathered feldspar- or quartz-rich clast, but exact identification requires a fre…
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Physical properties
Typically medium- to coarse-grained, strongly foliated, and sparkly from aligned biotite; hardness about 2.5–3 for biotite and 6–7 for quartz, with vitreous quartz luster and perfect mica cleavage. The tan central fragment appears to be a weathered feldspar- or quartz-rich clast, but exact identification requires a fresh surface and testing.
Formation & geological history
Formed when shale or volcanic protoliths underwent medium-grade regional metamorphism, commonly during mountain building; age depends on locality and may range from Precambrian to younger Paleozoic or Mesozoic terrains.
Uses & applications
Used locally as decorative stone, landscaping material, and occasionally thin building veneer; collector interest is generally modest unless the foliation, garnet, staurolite, or other porphyroblasts are prominent.
Geological facts
The glittering layers reflect cleavage surfaces of mica, while the planar fabric records directed pressure during metamorphism. Schistosity can make the rock split into thin slabs.
Field identification & locations
Look for platy, aligned dark mica flakes, pronounced layering, and light quartz/feldspar bands; common in regional metamorphic belts worldwide, including New England, the Appalachians, Scandinavia, and the Himalaya. A hand lens, streak test, and hardness test can refine identification.
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