metamorphic
Slate
Slate (Foliated Metamorphic Rock)
Hardness: 2.5–4 on the Mohs scale. Color: Dark gray to black, charcoal. Luster: Dull to silky (sub-vitreous). Structure: Fine-grained with strong slaty cleavage allowing it to split into thin flat sheets.
- Hardness
- 2
- Color
- Dark gray to black, charcoal
- Luster
- Dull to silky (sub-vitreous)
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Physical properties
Hardness: 2.5–4 on the Mohs scale. Color: Dark gray to black, charcoal. Luster: Dull to silky (sub-vitreous). Structure: Fine-grained with strong slaty cleavage allowing it to split into thin flat sheets.
Formation & geological history
Formed by low-grade regional metamorphism of shale, mudstone, or siltstone under low temperature and pressure conditions during mountain-building events.
Uses & applications
Used for roofing tiles, blackboards, billiard tables, flagstone paving, floor tiles, and ornamental garden landscaping.
Geological facts
Slate produces a characteristic dull ring sound when struck lightly. Historical chalkboards were made directly from large, smooth slabs of slate.
Field identification & locations
Identified in the field by its planar cleavage, smooth dull surface, and tendency to break into flat, sharp plates. Commonly found in folded mountainous metamorphic terrains.
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