metamorphic
Weathered gray metamorphic rock, likely slate or phyllite
Foliated metapelite; composition commonly quartz, mica, and chlorite
AI-generated identification · may be incorrectDark gray-green, fine-grained, with pale weathering rind and apparent planar foliation; likely Mohs 3–5, dull to silky luster, and strong cleavage along foliation. Exact identification is limited by the photograph.
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Physical properties
Dark gray-green, fine-grained, with pale weathering rind and apparent planar foliation; likely Mohs 3–5, dull to silky luster, and strong cleavage along foliation. Exact identification is limited by the photograph.
Formation & geological history
Formed when clay-rich sedimentary rock was buried and regionally metamorphosed under low-grade pressure and temperature, commonly during mountain building. Its age cannot be determined visually and depends on its source terrane.
Uses & applications
Slate may be used for roofing, paving, flooring, and writing surfaces; phyllite is mainly a decorative or teaching specimen. This piece has little commercial value unless it displays unusually attractive texture or mineralization.
Geological facts
The pale outer margin is likely weathering that altered iron-bearing minerals. Fine foliation and splitting into thin plates are more diagnostic than color alone.
Field identification & locations
Look for persistent planar layers, a fine texture, and fragments that split along cleavage; a silky sheen suggests phyllite, while flatter, duller surfaces suggest slate. Common in metamorphic belts worldwide, including Appalachians, Wales, and parts of the western United States.
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