metamorphic
Slate
Slate (Metamorphosed Mudstone/Shale)
Hardness: 2.5-4 Mohs; Color: Typically grey, can be black, green, or red; Luster: Dull/Matte; Crystal structure: Very fine-grained (microcrystalline); Cleavage: Perfect slaty cleavage (splits into thin, flat sheets); Specific Gravity: 2.7-2.8
- Hardness
- 2
- Color
- Typically grey, can be black, green, or red
- Luster
- Dull/Matte
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Physical properties
Hardness: 2.5-4 Mohs; Color: Typically grey, can be black, green, or red; Luster: Dull/Matte; Crystal structure: Very fine-grained (microcrystalline); Cleavage: Perfect slaty cleavage (splits into thin, flat sheets); Specific Gravity: 2.7-2.8
Formation & geological history
Formed through low-grade regional metamorphism of shale or mudstone under relatively low pressure and temperature conditions. It is typically found in folded mountain belts and can date from Precambrian to Cenozoic eras.
Uses & applications
Used extensively in the construction industry for roofing shingles, flooring, and billiard table tops. Historically used for blackboards and writing slates.
Geological facts
Slate is unique because it can be split into very thin sheets that are surprisingly durable and weather-resistant. Many European roofs have slate tiles that are over 100 years old and still functional.
Field identification & locations
Identify in the field by its distinct foliation (slaty cleavage) where the rock breaks in smooth, flat planes. It will 'ring' with a higher pitch than shale when struck with a hammer. Common in the Appalachian Mountains, Wales, and Brazil.
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