metamorphic
Slate
Foliated metamorphic rock (Slate)
Hardness: 2.5-4 Mohs; Color: Dark grey to bluish-black; Luster: Dull to satiny; Structure: Very fine-grained with distinct slaty cleavage; Cleavage: Perfect planar cleavage.
- Hardness
- 2
- Color
- Dark grey to bluish-black
- Luster
- Dull to satiny
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Physical properties
Hardness: 2.5-4 Mohs; Color: Dark grey to bluish-black; Luster: Dull to satiny; Structure: Very fine-grained with distinct slaty cleavage; Cleavage: Perfect planar cleavage.
Formation & geological history
Formed through low-grade regional metamorphism of shale or mudstone under relatively low pressure and temperature conditions. It is typically hundreds of millions of years old.
Uses & applications
Commonly used for roofing tiles, flooring, electrical panels, billiard table tops, and blackboards.
Geological facts
Slate can be split into very thin, flat sheets because of its foliation. It is extremely durable and has been used as a writing surface for centuries.
Field identification & locations
Identify in the field by its ability to split into thin sheets and its dull 'clink' sound when struck compared to the 'ring' of harder rocks. Commonly found in Appalachian Mountains and Wales.
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