metamorphic

Weathered slate or phyllite

Foliated metamorphic rock, commonly quartz–mica–chlorite assemblage

AI-generated identification · may be incorrect

Fine-grained, gray to tan, with strong planar cleavage and thin sheet-like fractures; dull to slightly silky luster. Hardness is approximately 3–5.5 Mohs, depending on mica and chlorite content; crystals are microscopic and aligned by foliation.

Identified September 18, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when shale or mudstone underwent low-grade regional metamorphism during mountain building, typically at temperatures of roughly 200–350°C. Exact geological age cannot be determined from the image.

Uses & applications

Used for roofing, flooring, paving, wall cladding, landscaping, and blackboard material; attractive phyllite may be collected as a field specimen. It is generally not a jewelry stone.

Geological facts

The specimen appears more weathered and coarser than typical roofing slate, so phyllite or transitional slate is plausible. Foliation reflects the reorientation of clay minerals into mica-rich layers.

Field identification & locations

Common in metamorphic belts worldwide, including the Appalachians, Wales, Vermont, and parts of the Alps. Identify it by its pervasive cleavage, fine grain, and ability to split along nearly parallel planes; a streak or hardness test can distinguish it from shale.