metamorphic
Slate
Phyllo-silicate based metamorphic rock
Hardness: 2.5-4 Mohs; Color: Dark grey to black; Luster: Dull to satiny; Structure: Foliated with fine-grained texture; Cleavage: Perfect slaty cleavage; Specific Gravity: 2.7-2.9
- Hardness
- 2
- Color
- Dark grey to black
- Luster
- Dull to satiny
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Physical properties
Hardness: 2.5-4 Mohs; Color: Dark grey to black; Luster: Dull to satiny; Structure: Foliated with fine-grained texture; Cleavage: Perfect slaty cleavage; Specific Gravity: 2.7-2.9
Formation & geological history
Formed through the low-grade regional metamorphism of shale or mudstone under relatively low pressure and temperature. It is often associated with ancient mountain-building events.
Uses & applications
Commonly used for roofing tiles, flooring, laboratory bench tops, billiard table tops, and blackboards due to its ability to be split into thin, flat sheets.
Geological facts
Because it splits into thin sheets, slate was historically used as writing slates and blackboards in schools. It is very resistant to chemicals and frost.
Field identification & locations
Identify in the field by its distinct foliation; it can be easily split into thin plates with a hammer. Found in areas of past tectonic activity like the Appalachian Mountains or Wales.
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