metamorphic
Slate
Foliated Metamorphic Rock
Hardness: 2.5-4 (Mohs); Color: Dark gray to black (can be green, red, or purple); Luster: Dull to satiny; Structure: Fine-grained with strong slaty cleavage; Gravity: 2.7-2.8
- Hardness
- 2
- Color
- Dark gray to black (can be green, red, or purple)
- Luster
- Dull to satiny
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Physical properties
Hardness: 2.5-4 (Mohs); Color: Dark gray to black (can be green, red, or purple); Luster: Dull to satiny; Structure: Fine-grained with strong slaty cleavage; Gravity: 2.7-2.8
Formation & geological history
Formed through low-grade regional metamorphism of shale, mudstone, or siltstone under high pressure and low heat, often during mountain-building events.
Uses & applications
Used extensively in construction for roofing shingles, floor tiles, billiard table tops, and historically for school blackboards and writing tablets.
Geological facts
Slate is unique for its ability to be split into thin, flat sheets. Some of the highest quality slate found in the United States comes from the Slate Valley of Vermont and New York.
Field identification & locations
Identified in the field by its planar surfaces and ability to ring or snap into plates when struck. Commonly found in folded mountain belts like the Appalachians or the Alps.
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