Chalk
“A billion tiny shells”
Sedimentary
Chalk is a soft, white, porous sedimentary rock made almost entirely of the microscopic calcium carbonate shells of marine plankton called coccolithophores. These organisms lived and died in warm, shallow seas during the Cretaceous Period.
Composition
calcite (from coccoliths), traces of flint and clay
Where Found
White Cliffs of Dover (England), Champagne (France), Denmark, Alabama (USA)
Mohs Hardness
1-2
Fun Fact
The Cretaceous Period gets its name from the Latin 'creta,' meaning chalk, because massive chalk deposits were laid down during that era.
Test Your Knowledge
Why did major chalk deposits form specifically during the Late Cretaceous Period?
Related Specimens
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