Claystone
“The finest sediment, solidified”
Claystone is a very fine-grained sedimentary rock composed predominantly of clay-sized particles less than 0.004 mm in diameter. It lacks the fissility (tendency to split into layers) of shale and often forms in the deepest, quietest parts of ancient lakes and ocean basins.
kaolinite, illite, montmorillonite, smectite, quartz
Great Plains (USA), London Clay (England), Paris Basin (France), widespread globally
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Bentonite, a type of claystone formed from weathered volcanic ash, can absorb up to five times its weight in water and is used in everything from cat litter to drilling mud.
Test Your Knowledge
Why is the clay mineral montmorillonite (found in some claystones) particularly problematic for construction?
Related Specimens
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