metamorphic
Likely biotite-rich schist or gneiss
Mica schist/gneiss; chiefly quartz, feldspar, and biotite mica
AI-generated identification · may be incorrectDark gray to black, coarse-grained, platy mica-rich texture with silvery reflections and possible foliation; Mohs hardness about 2.5–7 depending on mineral, vitreous to pearly luster, weak-to-distinct cleavage from mica.
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Physical properties
Dark gray to black, coarse-grained, platy mica-rich texture with silvery reflections and possible foliation; Mohs hardness about 2.5–7 depending on mineral, vitreous to pearly luster, weak-to-distinct cleavage from mica.
Formation & geological history
Formed when shale or igneous rock was subjected to elevated heat and pressure during regional metamorphism, commonly in Precambrian to Paleozoic mountain belts.
Uses & applications
Used locally as decorative building stone, facing, aggregate, and landscaping rock; attractive specimens may be collected, but this fragment has limited commercial value.
Geological facts
The reflective black flakes are likely biotite, while lighter angular grains are quartz or feldspar. Strong planar layering favors schist or gneiss over basalt.
Field identification & locations
Identify it by visible foliation, glittering mica flakes, and interlocking light minerals; common in metamorphic terrains such as the Appalachians, Canadian Shield, Alps, and Himalaya.
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