metamorphic
Slate
Slate (foliated metamorphic rock)
Hardness: 2.5–4 Mohs; Color: Gray, black, greenish-gray; Luster: Dull or satiny; Crystal Structure: Microcrystalline with slaty cleavage; Cleavage: Perfect planar cleavage.
- Hardness
- 2
- Color
- Gray, black, greenish-gray
- Luster
- Dull or satiny
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Physical properties
Hardness: 2.5–4 Mohs; Color: Gray, black, greenish-gray; Luster: Dull or satiny; Crystal Structure: Microcrystalline with slaty cleavage; Cleavage: Perfect planar cleavage.
Formation & geological history
Formed by the low-grade regional metamorphism of shale or mudstone. It develops through the compression of clay minerals in sedimentary deposits over millions of years, typically in tectonic settings.
Uses & applications
Used extensively in construction for roofing shingles, flooring, flagstones, and billiard table tops due to its durability and ability to be split into thin sheets.
Geological facts
Slate is renowned for its slaty cleavage, which allows it to split into extremely thin, flat plates. It was historically used for writing boards (slates) and chalkboards.
Field identification & locations
Identify in the field by its distinct layering and the way it breaks into flat slabs with a 'clinking' sound when struck. Common in mountainous regions with a history of tectonic activity.
