metamorphic
Slate
Low-grade Metamorphic Rock (composed of quartz, illite, chlorite)
Hardness: 2.5-4 Mohs; Color: dark grey to black but also green or purple; Luster: dull to sub-silky; Structure: fine-grained, slaty cleavage; Gravity: 2.6-2.9
- Hardness
- 2
- Color
- dark grey to black but also green or purple
- Luster
- dull to sub-silky
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Physical properties
Hardness: 2.5-4 Mohs; Color: dark grey to black but also green or purple; Luster: dull to sub-silky; Structure: fine-grained, slaty cleavage; Gravity: 2.6-2.9
Formation & geological history
Formed through low-grade regional metamorphism of shale or mudstone under high pressure and low temperature conditions. Commonly found in folded mountain belts.
Uses & applications
Used for roofing shingles, flooring tiles, billiard table tops, blackboards, and decorative stone landscaping.
Geological facts
Slate is unique for its ability to be split into thin, flat sheets due to its slaty cleavage. It is extremely durable and can last for centuries as a roofing material.
Field identification & locations
Identify by its ability to split into flat planes. Found in the Appalachian Mountains, Wales, and Brazil. Collectors look for flat pieces with sharp edges and distinct layering.
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