metamorphic
Slate
Slate (foliated metamorphic rock)
Mohs hardness: 2.5-4; Color: shades of gray, black, green, or purple; Luster: dull to earthy; Texture: very fine-grained with distinct slaty cleavage; Structure: foliated.
- Hardness
- 2
- Color
- shades of gray, black, green, or purple
- Luster
- dull to earthy
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Physical properties
Mohs hardness: 2.5-4; Color: shades of gray, black, green, or purple; Luster: dull to earthy; Texture: very fine-grained with distinct slaty cleavage; Structure: foliated.
Formation & geological history
Formed through low-grade regional metamorphism of shale or mudstone under low pressure and temperature conditions, typically within orogenic belts.
Uses & applications
Extensively used for roofing shingles, flooring tiles, billiard tables, blackboards, and garden landscaping due to its durability and ability to split into thin sheets.
Geological facts
Slate is prized for its low water absorption rate, making it an excellent material for roofing. The 'slaty cleavage' is caused by the parallel alignment of microscopic mica minerals.
Field identification & locations
Identify in the field by its distinct ability to split into thin, flat layers with a dull ring when struck. Commonly found in mountainous regions such as the Appalachian Mountains and Wales.
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