metamorphic
Slate
Foliated Metamorphic Rock
Hardness (Mohs): 2.5-4; Color: Grey, blue-grey; Luster: Dull to satiny; Crystal Structure: Microcrystalline; Cleavage: Excellent slaty cleavage; Specific Gravity: 2.7-2.8
- Color
- Grey, blue-grey
- Luster
- Dull to satiny
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Physical properties
Hardness (Mohs): 2.5-4; Color: Grey, blue-grey; Luster: Dull to satiny; Crystal Structure: Microcrystalline; Cleavage: Excellent slaty cleavage; Specific Gravity: 2.7-2.8
Formation & geological history
Formed through low-grade regional metamorphism of shale or mudstone under relatively low pressure and temperature. Common in mountainous regions with folded sedimentary layers.
Uses & applications
Used for roofing shingles, floor tiles, billiard table surfaces, electrical panels, and decorative garden landscaping.
Geological facts
Slate is unique because it can be split into very thin, flat sheets. Historically, it was widely used for writing tablets in schools before the invention of paper notebooks.
Field identification & locations
Identify by its ability to split into thin sheets along flat planes (foliation) and its 'clink' sound when struck. Commonly found in the Appalachian Mountains and Wales.
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