metamorphic
Slate
Foliated Metamorphic Slate
Hardness: 2.5-4 on the Mohs scale. Color: Dark grey to charcoal black. Luster: Dull to slightly silky. Structure: Fine-grained, microcrystalline with prominent slaty cleavage. Cleavage: Excellent parallel planar splitting.
- Hardness
- 2
- Color
- Dark grey to charcoal black
- Luster
- Dull to slightly silky
Identified More metamorphic →
Explore Slate in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 2.5-4 on the Mohs scale. Color: Dark grey to charcoal black. Luster: Dull to slightly silky. Structure: Fine-grained, microcrystalline with prominent slaty cleavage. Cleavage: Excellent parallel planar splitting.
Formation & geological history
Formed by low-grade regional metamorphism of shale or mudstone under relatively low temperature and pressure conditions, causing clay minerals to recrystallize into fine-grained micas aligned perpendicular to directional stress.
Uses & applications
Extensive use in construction as roofing tiles, flagstones, floor tiles, billiard table tops, and decorative landscaping ground cover.
Geological facts
Slate splits into thin, flat sheets due to its slaty cleavage, a property that made it historically ideal for writing tablets ('slate chalkboards') and durable roofing shingles that last over a century.
Field identification & locations
Identified in the field by its distinct fine-grained texture, dark color, and thin, flat cleavage planes. Widespread globally in ancient mountain belts; commonly used as crushed landscape gravel.
More like this
