metamorphic
Mica schist (likely garnet-mica schist)
Schist dominated by quartz, muscovite/biotite mica, and feldspar; possible almandine garnet
AI-generated identification · may be incorrectBrown-gray, strongly foliated, sparkly micaceous surface with platy cleavage and a pale quartz/feldspar vein or layer. Typical hardness is about 2–3 for mica-rich surfaces and 6–7 for quartz; generally low-to-moderate luster and very variable density.
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Physical properties
Brown-gray, strongly foliated, sparkly micaceous surface with platy cleavage and a pale quartz/feldspar vein or layer. Typical hardness is about 2–3 for mica-rich surfaces and 6–7 for quartz; generally low-to-moderate luster and very variable density.
Formation & geological history
Formed when shale or other clay-rich sediment was subjected to regional metamorphism, producing aligned mica layers and segregation of quartz-rich bands. Likely Precambrian in the Duluth–northeastern Minnesota region, though the exact age cannot be determined from the photograph.
Uses & applications
Used locally as decorative stone, landscaping material, and teaching or collecting specimens; strongly foliated schist is generally unsuitable for high-strength construction aggregate.
Geological facts
The glitter comes from mica flakes reflecting light, while the pale band is probably quartz. Individual mica sheets can be peeled along foliation. The image does not show diagnostic crystal faces, so garnet remains unconfirmed.
Field identification & locations
Commonly found in metamorphic terrains of northeastern Minnesota and adjacent Wisconsin. Look for glittery, aligned flakes and layers that split into slabs; a hardness test, streak test, and close inspection for red-brown garnets would improve identification.
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