metamorphic
Slate
Foliated Metamorphic Rock (composed of quartz, illite, chlorite)
Hardness: 2.5-4 Mohs; Color: Dark grey to black; Luster: Dull to satiny; Structure: Foliated with fine grains; Cleavage: Perfect slaty cleavage (breaks into flat planes)
- Hardness
- 2
- Color
- Dark grey to black
- Luster
- Dull to satiny
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Physical properties
Hardness: 2.5-4 Mohs; Color: Dark grey to black; Luster: Dull to satiny; Structure: Foliated with fine grains; Cleavage: Perfect slaty cleavage (breaks into flat planes)
Formation & geological history
Formed by low-grade regional metamorphism of shale or mudstone under low pressure and temperature conditions, typically in sedimentary basins.
Uses & applications
Extensively used for roofing tiles, flooring, electrical panels, chalkboards, and decorative landscaping.
Geological facts
Slate is renowned for its ability to split into thin, durable sheets. It was the primary material for school writing tablets throughout the 19th century.
Field identification & locations
Check for fine-grained texture and the ability to split into thin sheets along parallel planes. Found in metamorphic belts like the Appalachians or Wales.
