metamorphic
Dark gray metamorphic rock, likely slate or phyllite
Slate/phyllite; commonly quartz–mica–chlorite aggregate
AI-generated identification · may be incorrectFine-grained, dark gray, dull to subtly silky luster, with planar foliation and fractures. Typical hardness is about 2.5–4 (slate) or 3–4.5 (phyllite); composition and density cannot be confirmed from the image alone.
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Physical properties
Fine-grained, dark gray, dull to subtly silky luster, with planar foliation and fractures. Typical hardness is about 2.5–4 (slate) or 3–4.5 (phyllite); composition and density cannot be confirmed from the image alone.
Formation & geological history
Formed when shale or mudstone was regionally metamorphosed at low grade, commonly during mountain building. Its exact geological age depends on the source terrain; no age can be determined visually.
Uses & applications
Used for roofing, paving, floor and wall tiles, and decorative or educational specimens; attractive polished pieces may be collected but are generally low value.
Geological facts
The visible linear fabric and blocky splitting are characteristic of slaty cleavage or phyllitic foliation. A silky sheen would favor phyllite, while very smooth, planar cleavage favors slate.
Field identification & locations
Common in regional metamorphic belts worldwide, including Wales, the northeastern United States, Spain, and India. Test for repeated splitting along parallel planes and a streak that is usually gray; a photo cannot distinguish slate from phyllite confidently.
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