metamorphic
Slate / Greenschist
Foliated Metamorphic Rock (Greenschist/Slate)
Mohs hardness: 2.5-4; Color: Dark greyish-green to charcoal; Luster: Dull to pearly/satin; Texture: Fine-grained, foliated with slaty or schistose cleavage; Specific gravity: 2.7-2.9.
- Hardness
- 2
- Color
- Dark greyish-green to charcoal
- Luster
- Dull to pearly/satin
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Physical properties
Mohs hardness: 2.5-4; Color: Dark greyish-green to charcoal; Luster: Dull to pearly/satin; Texture: Fine-grained, foliated with slaty or schistose cleavage; Specific gravity: 2.7-2.9.
Formation & geological history
Formed by low-grade regional metamorphism of shale, clay, or mafic volcanic rocks under directed pressure and mild temperature. Typically dates from Precambrian to Cenozoic mountain-building periods.
Uses & applications
Used historically and modernly in roofing tiles, flooring, billiard tables, blackboards, and decorative landscaping stones.
Geological facts
Slate breaks easily along flat, parallel planes of foliation due to alignment of microscopic sheet silicates like chlorite and muscovite.
Field identification & locations
Identified by its distinctive fissility (splits into thin sheets), dull sheen, fine grain, and characteristic dark greenish-grey color. Commonly found in regions with ancient or active collisional mountain belts.
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