metamorphic
Dark gray foliated metamorphic rock, likely slate or phyllite
Slate/phyllite; chiefly quartz, mica, and chlorite
AI-generated identification · may be incorrectTypically fine-grained, dark gray, with a dull to silky luster and strong planar cleavage; hardness about 2.5–4. Slate breaks into thin flat sheets, while phyllite commonly shows a subtle silky sheen. The photograph is insufficient for confident species-level identification.
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Physical properties
Typically fine-grained, dark gray, with a dull to silky luster and strong planar cleavage; hardness about 2.5–4. Slate breaks into thin flat sheets, while phyllite commonly shows a subtle silky sheen. The photograph is insufficient for confident species-level identification.
Formation & geological history
Formed when shale or mudstone is regionally metamorphosed under low-grade pressure and temperature, commonly during mountain building. Its exact geological age depends on the source formation.
Uses & applications
Slate is used for roofing, tiles, paving, and writing surfaces; phyllite is mainly decorative or a collector specimen. Small hand specimens generally have limited commercial value.
Geological facts
The visible layering/foliation is metamorphic cleavage rather than ordinary sedimentary bedding. A streak or scratch test and examination of the fresh break can distinguish slate from phyllite.
Field identification & locations
Common in metamorphic belts worldwide, including Wales, the eastern United States, the Alps, and parts of China. Look for planar splitting, fine grain size, and mica-rich sheen; avoid confusing it with schist, which has larger visible crystals.
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