metamorphic
Slate
Slate (Low-grade foliated metamorphic rock)
Hardness: 2.5-4 (Mohs scale); Color: Typically grey, charcoal, or bluish-grey; Luster: Dull to satiny; Structure: Fine-grained, foliated with distinct slaty cleavage; Cleavage: Perfect planar cleavage.
- Hardness
- 2
- Color
- Typically grey, charcoal, or bluish-grey
- Luster
- Dull to satiny
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Physical properties
Hardness: 2.5-4 (Mohs scale); Color: Typically grey, charcoal, or bluish-grey; Luster: Dull to satiny; Structure: Fine-grained, foliated with distinct slaty cleavage; Cleavage: Perfect planar cleavage.
Formation & geological history
Formed through low-grade regional metamorphism of shale or mudstone under high pressure and relatively low temperatures. Often dates back to the Paleozoic era in major mountain-building belts.
Uses & applications
Extensively used in construction for roofing shingles, floor tiles, and billiard table tops. Also used for blackboards, whetstones, and cemetery headstones.
Geological facts
Slate is unique because it can be split into extremely thin, durable sheets due to its slaty cleavage. It was the primary material for school writing tablets throughout the 18th and 19th centuries.
Field identification & locations
Identify in the field by its ability to split into thin flat layers and its 'clink' sound when struck. Found in mountainous regions like the Appalachians (USA), Wales (UK), and Brazil.
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