metamorphic
Slate
Metamorphic Rock (Fine-grained)
Hardness: 2.5-4 on the Mohs scale. Color: Typically gray, ranging from light gray to dark gray, but can also be green, red, black, purple, or brown. Luster: Dull to somewhat silky. Crystal structure: Microcrystalline, composed mostly of clay minerals or micas.…
- Hardness
- 2
- Luster
- Dull to somewhat silky
Identified More metamorphic →
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Physical properties
Hardness: 2.5-4 on the Mohs scale. Color: Typically gray, ranging from light gray to dark gray, but can also be green, red, black, purple, or brown. Luster: Dull to somewhat silky. Crystal structure: Microcrystalline, composed mostly of clay minerals or micas. Cleavage: Excellent slaty cleavage allowing it to break into thin, smooth sheets. Specific gravity: 2.6-2.8.
Formation & geological history
Formed by the low-grade regional metamorphism of mudstone, shale, or sometimes basalt, under relatively low temperatures and directed pressure, typically during tectonic mountain-building events.
Uses & applications
Widely used for roofing, flooring, paving, pool tables, and historically for writing slates and blackboards.
Geological facts
Slate's ability to split into thin, durable sheets makes it one of the premier roofing materials used for centuries in architecture worldwide.
Field identification & locations
Identified by its fine-grained texture, dull luster, and characteristic ability to split into flat, thin sheets along planes independent of original bedding. Common in regions with a history of mountain building, such as Wales, the northeastern United States, and parts of Europe.
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