metamorphic
Slate Pebble
Low-grade Metamorphosed Shale (Slate)
Hardness: 2.5-4 Mohs; Color: Gray, bluish-gray, or greenish-gray; Luster: Dull to slightly silky; Crystal Structure: Microcrystalline; Cleavage: Excellent slaty cleavage (striations visible); Specific Gravity: 2.7-2.8
- Hardness
- 2
- Color
- Gray, bluish-gray, or greenish-gray
- Luster
- Dull to slightly silky
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Physical properties
Hardness: 2.5-4 Mohs; Color: Gray, bluish-gray, or greenish-gray; Luster: Dull to slightly silky; Crystal Structure: Microcrystalline; Cleavage: Excellent slaty cleavage (striations visible); 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 conditions. This specimen has been rounded and smoothed by water erosion, likely in a river or coastal environment.
Uses & applications
Used in roofing, flooring, billiards tables, and decorative landscaping. Small pebbles are often used in aquariums or as garden mulch.
Geological facts
Slate is unique for its slaty cleavage, which allows it to be split into thin, flat sheets. The grayish-blue color is typically due to the presence of carbonaceous material or iron sulfides.
Field identification & locations
Identify in the field by its fine-grained texture, distinct layering (foliation), and the way it can be split into flat planes. Found abundantly in Appalachian regions of the US, Wales, and Brazil.
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