metamorphic

Dark gray foliated metamorphic rock, likely slate or phyllite

Slate/phyllite; chiefly quartz, mica, and chlorite

AI-generated identification · may be incorrect

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.

Identified August 14, 2026More metamorphic →

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Physical properties

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.