metamorphic
Slate
Foliated Metamorphic Rock
Hardness (Mohs): 2.5-4; Color: Grey, black, or blue-grey; Luster: Dull; Structure: Foliated with fine-grained texture; Cleavage: Perfect slaty cleavage; Specific Gravity: 2.7-2.8
- Color
- Grey, black, or blue-grey
- Luster
- Dull
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Physical properties
Hardness (Mohs): 2.5-4; Color: Grey, black, or blue-grey; Luster: Dull; Structure: Foliated with fine-grained texture; Cleavage: Perfect slaty cleavage; Specific Gravity: 2.7-2.8
Formation & geological history
Formed through the low-grade metamorphism of shale or mudstone under low pressure and temperature conditions. It is typically associated with regional metamorphism in mountain-building regions.
Uses & applications
Extensively used in construction for roofing tiles, flooring, and flagstones. Also used for billiard table tops, blackboards, and small decorative items.
Geological facts
The ability of slate to be split into thin, flat sheets is known as 'slaty cleavage,' which is caused by the parallel alignment of microscopic mica crystals during metamorphism.
Field identification & locations
Identify in the field by its distinct ability to split into thin, flat plates and its 'clink' sound when struck. Commonly found in folded mountain belts like the Appalachians or the Alps.
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