metamorphic
Slate
Slate; primarily fine-grained mica, chlorite, quartz, and clay minerals
AI-generated identification · may be incorrectTypically dark gray to black, very fine-grained, dull to slightly silky, with excellent slaty cleavage that produces thin, flat, sharp-edged flakes. Hardness is about 3–4 Mohs; specific gravity is approximately 2.7–2.8.
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Physical properties
Typically dark gray to black, very fine-grained, dull to slightly silky, with excellent slaty cleavage that produces thin, flat, sharp-edged flakes. Hardness is about 3–4 Mohs; specific gravity is approximately 2.7–2.8.
Formation & geological history
Slate forms when shale or mudstone undergoes low-grade regional metamorphism, commonly during mountain building, causing aligned microscopic minerals and strong cleavage. It may range from Paleozoic to much younger geological ages.
Uses & applications
Used for roofing, floor and wall tiles, paving, blackboards, writing tablets, and architectural cladding; attractive specimens are collected but generally have modest value.
Geological facts
The specimen’s thin, planar fragments and dark fine texture are characteristic of slate, though weathered shale or phyllite can look similar.
Field identification & locations
Identify it by its ability to split into smooth, parallel sheets without visible large crystals; common sources include metamorphic belts worldwide, especially Wales, Spain, Brazil, and the northeastern United States.
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