metamorphic
Slate
Slate (Low-grade regional metamorphic rock)
Hardness: 2.5-4 Mohs; color: grey, blue-grey, or reddish-brown due to iron oxides; luster: dull to slightly pearly; structure: fine-grained, foliated with slaty cleavage; specific gravity: 2.7-2.8.
- Hardness
- 2
- Color
- grey, blue-grey, or reddish-brown due to iron oxides
- Luster
- dull to slightly pearly
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Physical properties
Hardness: 2.5-4 Mohs; color: grey, blue-grey, or reddish-brown due to iron oxides; luster: dull to slightly pearly; structure: fine-grained, foliated with slaty cleavage; specific gravity: 2.7-2.8.
Formation & geological history
Formed through the low-grade regional metamorphism of shale or mudstone under low pressure and temperature conditions. It consists mainly of quartz, chlorite, and mica minerals.
Uses & applications
Commonly used for roofing shingles, flooring tiles, billiard tables, and chalkboard surfaces due to its durability and ability to split into thin sheets.
Geological facts
Slate can be split into very thin slabs while maintaining high strength; this property is known as 'slaty cleavage.' In the 18th and 19th centuries, it was the primary material for school writing tablets.
Field identification & locations
Identified by its ability to break into flat, smooth planes and its 'tinkling' sound when struck. Commonly found in mountainous regions or areas with a history of tectonic activity. Look for thin, parallel layers.
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