metamorphic
Black Slate
Slate (Metamorphic Rock)
Hardness: 2.5-4 on Mohs scale. Color: Dark grey to black. Luster: Dull to slightly satiny. Grain size: Very fine-grained. Cleavage: Perfect slaty cleavage, splits into thin flat sheets. Specific gravity: 2.6-2.8.
- Hardness
- 2
- Color
- Dark grey to black
- Luster
- Dull to slightly satiny
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Physical properties
Hardness: 2.5-4 on Mohs scale. Color: Dark grey to black. Luster: Dull to slightly satiny. Grain size: Very fine-grained. Cleavage: Perfect slaty cleavage, splits into thin flat sheets. Specific gravity: 2.6-2.8.
Formation & geological history
Formed by low-grade regional metamorphism of shale, mudstone, or siltstone under relatively low temperature and pressure conditions, causing clay minerals to recrystallize into fine-grained micas aligned perpendicular to compressive stress.
Uses & applications
Widely used for roofing tiles, flooring, flagstones, billiard tables, blackboards, and decorative stone in landscaping.
Geological facts
Slate can preserve tiny fossils from its original sedimentary parent rock. It is famous for its ability to split along smooth parallel planes, a property known as slaty cleavage.
Field identification & locations
Identified in the field by its dark color, fine grain, parallel layering (slaty cleavage), and dull ring when struck lightly. Commonly found in folded mountainous regions worldwide such as Wales, Spain, and Pennsylvania.
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