metamorphic

Foliated shale or slate fragment

Fine-grained phyllite/slate, composed mainly of clay minerals, mica, and quartz

AI-generated identification · may be incorrect

Dark gray-brown, thinly layered, and dull to slightly silky; very fine grained with strong planar cleavage. Likely Mohs hardness 2–4; specific gravity approximately 2.6–2.8. The shiny surface may indicate mica-rich phyllite rather than ordinary shale.

Identified September 19, 2026More metamorphic →

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Physical properties

Formation & geological history

This is most consistent with low-grade metamorphism of clay-rich mudstone, compacting and recrystallizing sediment into slate or phyllite. Such rocks commonly formed during Paleozoic–Mesozoic mountain-building events, though age cannot be determined from the image.

Uses & applications

Used as roofing slate, paving, wall cladding, blackboards, and decorative stone; small fragments are mainly collector or educational specimens.

Geological facts

The specimen breaks along closely spaced cleavage planes, producing thin sheets. A silky sheen and slightly wavy foliation favor phyllite; flatter, duller cleavage favors slate or shale.

Field identification & locations

Identify it by its laminated texture, fine grain, dark color, and tendency to split into plates; a streak test, hardness test, and thin-section examination would distinguish shale, slate, and phyllite. Common in metamorphic belts worldwide.