metamorphic
Blue-gray metamorphic rock, likely slate or schist
Foliated phyllite–schist; chiefly quartz, mica, and chlorite (exact identification requires testing)
AI-generated identification · may be incorrectDark blue-gray, fine-grained, with a dull to slight silky luster and visible foliation; probable Mohs hardness 2–3 across mica-rich surfaces and 6–7 for quartz grains. Layering and irregular cleavage appear present.
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Physical properties
Dark blue-gray, fine-grained, with a dull to slight silky luster and visible foliation; probable Mohs hardness 2–3 across mica-rich surfaces and 6–7 for quartz grains. Layering and irregular cleavage appear present.
Formation & geological history
Formed when shale or mudstone underwent low- to medium-grade regional metamorphism, recrystallizing clay minerals into mica; commonly Paleozoic or older, though age cannot be determined visually.
Uses & applications
Used locally for roofing, paving, wall stone, and aggregate; attractive specimens may be collected, but this small piece has limited commercial value.
Geological facts
A silky sheen and thin, wavy cleavage would favor phyllite; coarser visible mica and stronger schistosity would favor schist. The blue color may reflect chlorite, graphite, or weathering rather than a distinct mineral.
Field identification & locations
Common in metamorphic belts worldwide, including the Appalachians, New England, Wales, and the Alps. Check for foliation, ability to split into sheets, a glassy quartz streak, and lack of reaction with dilute acid.
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