sedimentary
Shale
Fissile mudstone (primarily clay minerals and silt-sized quartz)
Hardness: 3 on Mohs scale; Color: typically gray, brown, or black; Luster: dull/earthy; Crystal structure: lacks visible crystals; cleavage: fissile (splits into thin layers); Specific gravity: 2.4-2.8
- Hardness
- 3 on Mohs scale
- Color
- typically gray, brown, or black
- Luster
- dull/earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: typically gray, brown, or black; Luster: dull/earthy; Crystal structure: lacks visible crystals; cleavage: fissile (splits into thin layers); Specific gravity: 2.4-2.8
Formation & geological history
Formed through the compaction and lithification of silt and clay-sized mineral particles (mud) in slow-moving water environments like lagoons, floodplains, and deep ocean basins.
Uses & applications
Used in the production of cement, bricks, and tile. Fine-grained organic-rich shales are major sources of natural gas and petroleum (shale gas).
Geological facts
Shale is the most common sedimentary rock on Earth, making up an estimated 70 percent of the earth's crustal rocks. It often contains well-preserved fossils due to the fine grain size.
Field identification & locations
Identify in the field by its distinct layering and tendency to flake apart into thin, flat plates when struck. It is found globally in sedimentary basins.
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