metamorphic
Likely slate fragment
Slate; fine-grained foliated metamorphic rock composed mainly of clay minerals, quartz, and mica
AI-generated identification · may be incorrectDark gray, dull to slightly silky luster, very fine grained, and strongly cleavable into thin slabs; hardness about 2.5–4 Mohs. The pale rough edge may be a weathered or mineral-coated surface; the image does not show diagnostic crystals.
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Physical properties
Dark gray, dull to slightly silky luster, very fine grained, and strongly cleavable into thin slabs; hardness about 2.5–4 Mohs. The pale rough edge may be a weathered or mineral-coated surface; the image does not show diagnostic crystals.
Formation & geological history
Forms when shale or mudstone undergoes low-grade regional metamorphism, commonly during mountain building. Its age depends on the source formation and cannot be determined from the photograph.
Uses & applications
Used for roofing, floor and wall tiles, paving, billiard tables, and landscaping; attractive thin pieces may be collected but usually have little monetary value.
Geological facts
Slate’s defining feature is slaty cleavage, produced by aligned microscopic mica and clay minerals. It can resemble shale, schist, dark siltstone, or manufactured stone in a photograph.
Field identification & locations
Look for planar splitting into smooth, parallel sheets, a fine texture, and a streak that is usually pale gray. Common sources include metamorphic belts worldwide, especially Wales, Vermont, Spain, Brazil, and China; a hardness, streak, and acid test would improve identification.
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