metamorphic
Slate
Slate (Metamorphic Rock)
Hardness: 2.5-4 on Mohs scale. Color: Dark gray to black (can also be green, red, or purple). Luster: Dull to satin. Foliated texture with fine-grained slaty cleavage that allows it to split into thin, flat sheets.
- Hardness
- 2
- Color
- Dark gray to black (can also be green, red, or purple)
- Luster
- Dull to satin
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Physical properties
Hardness: 2.5-4 on Mohs scale. Color: Dark gray to black (can also be green, red, or purple). Luster: Dull to satin. Foliated texture with fine-grained slaty cleavage that allows it to split into thin, flat sheets.
Formation & geological history
Formed by low-grade regional metamorphism of shale, mudstone, or siltstone under low heat and directed pressure, compressing clay minerals into parallel microscopic sheets.
Uses & applications
Widely used for roofing tiles, flooring, flagstones, billiard table tops, blackboards, landscaping, and decorative stonework.
Geological facts
Slate splits into thin, flat panels along its natural cleavage planes. Highly durable, fireproof, and resistant to atmospheric weathering, slate roofs can last over 100 years.
Field identification & locations
Identified in the field by its planar fissility, fine grain size, non-glossy dark surface, and sharp metallic ring when struck lightly. Commonly found in mountainous or metamorphosed regions such as Wales, Spain, Brazil, and the Appalachian region of North America.
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