metamorphic
Slate
Slate; predominantly fine-grained phyllosilicates, commonly muscovite/illite and chlorite with quartz
AI-generated identification · may be incorrectVery fine-grained, gray-brown, dull to silky luster, low-grade metamorphic foliation and strong slaty cleavage visible as thin layers. Hardness is about 3–4 Mohs; specific gravity approximately 2.7–2.8.
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Physical properties
Very fine-grained, gray-brown, dull to silky luster, low-grade metamorphic foliation and strong slaty cleavage visible as thin layers. Hardness is about 3–4 Mohs; specific gravity approximately 2.7–2.8.
Formation & geological history
Formed when shale or mudstone undergoes low-grade regional metamorphism, typically during mountain building. Its exact geological age cannot be determined from the photograph; slate occurs in rocks ranging from Precambrian to recent mountain belts.
Uses & applications
Used for roofing, flooring, paving, wall cladding, gravestones, pool tables, and decorative tiles; attractive pieces are collected but usually have modest value.
Geological facts
The specimen’s planar splitting and fine layering are characteristic of slaty cleavage, produced by aligned microscopic clay-derived minerals rather than original sedimentary bedding.
Field identification & locations
Identify it by its fine texture, layered appearance, and ability to split into thin, relatively flat sheets; it commonly occurs in metamorphic belts worldwide, including Wales, Vermont, Spain, Brazil, and China.
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