metamorphic
Slate
Slate (foliated metamorphic rock composed mainly of quartz, illite, and chlorite)
Hardness: 2.5-4 on Mohs scale; Color: Grey, blue-grey, or greenish-grey; Luster: Dull to pearly; Texture: Fine-grained with prominent slaty cleavage
- Hardness
- 2
- Color
- Grey, blue-grey, or greenish-grey
- Luster
- Dull to pearly
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Physical properties
Hardness: 2.5-4 on Mohs scale; Color: Grey, blue-grey, or greenish-grey; Luster: Dull to pearly; Texture: Fine-grained with prominent slaty cleavage
Formation & geological history
Formed through low-grade regional metamorphism of shale or mudstone under low heat and pressure. Commonly found in former sedimentary basins transformed by mountain-building events.
Uses & applications
Historically used for roofing tiles, writing slates, billiard table tops, and flooring; also collected as common river pebble specimens.
Geological facts
Slate splits into thin, flat sheets along parallel planes of alignment known as slaty cleavage, which is perpendicular to the direction of metamorphic compression.
Field identification & locations
Identified by its fine grain, smooth river-worn shape, cool grey tone, and tendencies to break into flat fragments or thin sheets. Abundant along river beds, beaches, and slate quarry regions worldwide.
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