sedimentary
Chalk
Calcium Carbonate (CaCO3)
Hardness: 1-3 Mohs; Color: White to grey; Luster: Dull/Earthy; Structure: Fine-grained, porous; Cleavage: None/Earth fracture; Specific Gravity: 2.3-2.6
- Hardness
- 1-3 Mohs
- Color
- White to grey
- Luster
- Dull/Earthy
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Physical properties
Hardness: 1-3 Mohs; Color: White to grey; Luster: Dull/Earthy; Structure: Fine-grained, porous; Cleavage: None/Earth fracture; Specific Gravity: 2.3-2.6
Formation & geological history
Formed in deep marine environments from the accumulation of microscopic skeletal remains (coccoliths) of algae over millions of years, primarily during the Cretaceous period.
Uses & applications
Used in the manufacture of lime, cement, and blackboard chalk. Also used in agriculture to neutralize acidic soil and as a filler in paper and plastics.
Geological facts
The White Cliffs of Dover are the most famous example of chalk formations. Under a microscope, chalk is revealed to be composed almost entirely of the plates of tiny marine algae.
Field identification & locations
Identify by its soft, powdery texture and its reaction (fizzing) when exposed to dilute hydrochloric acid. It is very common in coastal regions of Western Europe.
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