metamorphic
Slate
Slate (Foliated Metamorphic Rock)
Hardness: 2.5-4 Mohs; color: dark gray to black; luster: dull to slightly silky; structure: fine-grained, foliated with slaty cleavage; cleavage: perfect basal cleavage into thin sheets.
- Hardness
- 2
- Color
- dark gray to black
- Luster
- dull to slightly silky
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Physical properties
Hardness: 2.5-4 Mohs; color: dark gray to black; luster: dull to slightly silky; structure: fine-grained, foliated with slaty cleavage; cleavage: perfect basal cleavage into thin sheets.
Formation & geological history
Formed through the regional metamorphism of shale or mudstone under low-grade pressure and temperature conditions. It typically dates to various geological eras depending on regional tectonic history.
Uses & applications
Commonly used for roofing shingles, flooring tiles, billiard table tops, blackboards, and decorative stone in landscaping.
Geological facts
Slate is unique because it can be split into very thin, flat sheets. Historically, it was the primary material for writing tablets in schools during the 19th century.
Field identification & locations
Identified in the field by its fine-grained texture and ability to split into flat planes. It will often produce a 'tink' sound when struck with a hammer. Commonly found in mountainous regions like the Appalachians or North Wales.
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