metamorphic
Slate
Slate (foliated metamorphic rock)
Mohs hardness: 2.5-4; Color: Grey, black, or blue-grey; Luster: Dull/earthy; Structure: Fine-grained, foliated with excellent slaty cleavage; S.G.: 2.7-2.8
- Hardness
- 2
- Color
- Grey, black, or blue-grey
- Luster
- Dull/earthy
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Physical properties
Mohs hardness: 2.5-4; Color: Grey, black, or blue-grey; Luster: Dull/earthy; Structure: Fine-grained, foliated with excellent slaty cleavage; S.G.: 2.7-2.8
Formation & geological history
Formed by low-grade regional metamorphism of shale or mudstone under relatively low temperature and pressure conditions, typically in ancient sedimentary basins throughout various geological eras.
Uses & applications
Widely used for roofing tiles, flooring, laboratory bench tops, billiard table tops, and blackboards due to its durability and ability to split into thin sheets.
Geological facts
Slate is essentially lithified mud. It can be split into very thin sheets because its mica minerals align perfectly perpendicular to the direction of metamorphic compression.
Field identification & locations
Identified in the field by its tendency to break along flat, parallel planes (slaty cleavage) and its dull appearance. It is common in Appalachian mountains and regions like Wales, UK.
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