metamorphic

Dark metamorphic pebble, likely slate or phyllite

Slate/phyllite; chiefly fine-grained mica and quartz, with possible chlorite and graphite

AI-generated identification · may be incorrect

Dark gray-black, fine-grained, dull to faintly silky luster, and rounded by water or abrasion. Likely Mohs hardness 2.5–4; weak planar cleavage or foliation may be visible, but mineral identification is uncertain from the photograph.

Identified September 5, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when clay-rich sedimentary rock was subjected to low-grade regional metamorphism, commonly during mountain building; age depends on its source terrain. Its smooth shape indicates stream, beach, or glacial transport.

Uses & applications

Suitable mainly as a teaching or decorative specimen; slate may be used for roofing, tiles, paving, and writing surfaces, while phyllite has limited construction use.

Geological facts

Slate splits into thin sheets, whereas phyllite commonly shows a satiny sheen and crinkled foliation. The specimen could also be another dark metamorphic rock, such as fine-grained schist.

Field identification & locations

Look for planar splitting, aligned mica flakes, and a streak that is usually gray rather than metallic black; a hardness, streak, and acid test would improve identification. Common in metamorphic mountain belts worldwide.