metamorphic
Slate
Slate (Metamorphosed Shale or Mudstone)
AI-generated identification · may be incorrectHardness: 2.5-4 (Mohs); Color: Dark grey, charcoal, or bluish-grey; Luster: Dull to pearly; Crystal structure: Fine-grained, microcrystalline; Cleavage: Perfect slaty cleavage (breaks into flat sheets)
- Hardness
- 2
- Color
- Dark grey, charcoal, or bluish-grey
- Luster
- Dull to pearly
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Physical properties
Hardness: 2.5-4 (Mohs); Color: Dark grey, charcoal, or bluish-grey; Luster: Dull to pearly; Crystal structure: Fine-grained, microcrystalline; Cleavage: Perfect slaty cleavage (breaks into flat sheets)
Formation & geological history
Formed by low-grade regional metamorphism of shale, mudstone, or volcanic ash under relatively low pressure and temperature. It is commonly found in fold belts across various geological ages.
Uses & applications
Traditionally used for roofing tiles, chalkboards, billiard table tops, flooring, and landscaping. It is also used as decorative stone in gardens.
Geological facts
Slate can split into very thin sheets because its mica minerals were flattened and aligned during metamorphism. It is one of the most durable natural building materials, lasting over a century on roofs.
Field identification & locations
Identified in the field by its distinct thin layering and tendency to ring slightly when struck. It is commonly found in mountainous regions such as North Wales, the Appalachians, and the Alps.
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