metamorphic
Foliated metamorphic rock (likely slate or phyllite)
Slate/phyllite; chiefly quartz, mica, and chlorite
AI-generated identification · may be incorrectDark gray, fine-grained, with visible foliation and planar splitting; dull to subtly silky luster. Hardness is typically 3–4 for phyllite and 5–6 for slate, with negligible cleavage beyond its strong slaty cleavage.
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Physical properties
Dark gray, fine-grained, with visible foliation and planar splitting; dull to subtly silky luster. Hardness is typically 3–4 for phyllite and 5–6 for slate, with negligible cleavage beyond its strong slaty cleavage.
Formation & geological history
Formed when shale or mudstone underwent low-grade regional metamorphism during mountain building, commonly hundreds of millions of years old. The pale streaks may be quartz or calcite veins.
Uses & applications
Used for roofing, paving, flooring, wall cladding, and landscaping; attractive pieces may be collected, though this specimen appears ordinary field rock.
Geological facts
Slate has a very fine texture and sharply planar cleavage; phyllite has a more pronounced silky sheen and wavy foliation. The image’s sheen and deformation suggest phyllite, but laboratory tests are needed for certainty.
Field identification & locations
Common in metamorphic belts worldwide, including the Appalachians, Wales, and New England. Examine fresh surfaces, foliation, and reaction to dilute hydrochloric acid; fizzing indicates calcite veins rather than the main rock.
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