metamorphic
Slate
Foliated Metamorphic Rock
Hardness: 2.5-4 Mohs; color: dark grey to black; luster: dull; crystal structure: fine-grained (microcrystalline); cleavage: perfect slaty cleavage; specific gravity: 2.7-2.8
- Hardness
- 2
- Color
- dark grey to black
- Luster
- dull
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Physical properties
Hardness: 2.5-4 Mohs; color: dark grey to black; luster: dull; crystal structure: fine-grained (microcrystalline); cleavage: perfect slaty cleavage; specific gravity: 2.7-2.8
Formation & geological history
Formed through low-grade regional metamorphism of shale or mudstone under relatively low pressure and temperature conditions. Typically found in ancient mountain belts.
Uses & applications
Commonly used for roofing shingles, flooring, billiard table tops, blackboards, and decorative landscaping. Occasionally used in jewelry for its smooth texture.
Geological facts
Slate is unique for its ability to be split into thin, flat sheets. Some of the world's most famous slate comes from Wales, which was the slate capital of the world during the 19th century.
Field identification & locations
Identify by its tendency to break into flat planes and its dull, matte finish. Commonly found in riverbeds or mountainous regions with folded rock layers. Collectors value pieces with fossil impressions or unique mineral inclusions.
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