metamorphic
Slate
Slate (Foliated Metamorphic Rock)
Hardness: 2.5-4 Mohs; color: grey, black, brownish-gold (due to oxidation); luster: dull to slightly pearly; structure: fine-grained, foliated with slaty cleavage; cleavage: perfect planar.
- Hardness
- 2
- Color
- grey, black, brownish-gold (due to oxidation)
- Luster
- dull to slightly pearly
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Physical properties
Hardness: 2.5-4 Mohs; color: grey, black, brownish-gold (due to oxidation); luster: dull to slightly pearly; structure: fine-grained, foliated with slaty cleavage; cleavage: perfect planar.
Formation & geological history
Formed through low-grade regional metamorphism of shale or mudstone under relatively low pressure and temperature. It is typically hundreds of millions of years old, often dating back to the Paleozoic era.
Uses & applications
Extensively used for roofing tiles, flooring, outdoor paving, blackboards, and billiard table tops due to its durability and ability to split into thin sheets.
Geological facts
Slate is waterproof and fireproof, making it one of the most durable natural roofing materials available. The specific rusty colors seen in this specimen are caused by the weathering and oxidation of iron-bearing minerals like pyrite.
Field identification & locations
Identified by its fine grain and 'slaty cleavage'—the tendency to break into flat, thin plates. Found commonly in mountainous regions with a history of tectonic activity, such as Vermont, Wales, and Brazil.
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