metamorphic
Fine-grained dark metamorphic rock, likely slate or phyllite
Slate/phyllite; chiefly quartz, mica, and chlorite
AI-generated identification · may be incorrectGray-green, dull to slightly silky, fine-grained, with a weak planar foliation and uneven fracture. Typical hardness is about 3–6 Mohs; individual mineral grains are too small to identify confidently from the image.
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Physical properties
Gray-green, dull to slightly silky, fine-grained, with a weak planar foliation and uneven fracture. Typical hardness is about 3–6 Mohs; individual mineral grains are too small to identify confidently from the image.
Formation & geological history
Formed when shale or mudstone underwent low-grade regional metamorphism, commonly during mountain building. Its exact geological age cannot be determined visually and depends on locality.
Uses & applications
Used historically for roofing, floor tiles, paving, writing slates, and crushed aggregate; attractive pieces may be collected, though this specimen appears ordinary.
Geological facts
The foliation reflects alignment of microscopic clay-derived minerals during compression and recrystallization. A silky sheen would favor phyllite, while strong flat splitting would favor slate.
Field identification & locations
Common in metamorphic belts worldwide, including Wales, the northeastern United States, the Appalachians, and parts of Canada. Test for thin planar splitting, a fine texture, and possible mica sheen; a locality is needed for a firm identification.
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