metamorphic
Blue-gray metamorphic rock, likely slate or phyllite
Slate/phyllite; chiefly quartz, muscovite/illite, chlorite, and minor feldspar
AI-generated identification · may be incorrectFine-grained, blue-gray to lavender, with a dull to silky sheen and visible planar layering/foliation; typically Mohs 3–5 and splits along cleavage. The sparkly surface suggests phyllite or mica-rich slate rather than ordinary shale.
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Physical properties
Fine-grained, blue-gray to lavender, with a dull to silky sheen and visible planar layering/foliation; typically Mohs 3–5 and splits along cleavage. The sparkly surface suggests phyllite or mica-rich slate rather than ordinary shale.
Formation & geological history
Formed when shale or mudstone underwent low-grade regional metamorphism during mountain building; ages depend on locality, commonly Paleozoic or older. Foliation developed as clay minerals recrystallized under directed pressure.
Uses & applications
Used for roofing, floor and wall tiles, paving, writing slabs, and landscaping; attractive pieces are collected but this specimen appears modest in gem value.
Geological facts
Phyllite commonly shows a satin-like reflective sheen caused by aligned microscopic mica, whereas slate has flatter, sharper cleavage and a duller surface.
Field identification & locations
Identify it by fine foliation, planar splitting, lack of visible large crystals, and a streak that is usually pale gray; it is commonly found in metamorphic belts worldwide, including Wales, Vermont, Spain, and the Appalachians.
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