sedimentary
Chalk
CaCO3 (Calcium Carbonate)
Hardness: 1 on Mohs scale; Color: White to light grey; Luster: Dull/Earthy; Structure: Fine-grained, porous; Cleavage: None/Conchoidal.
- Hardness
- 1 on Mohs scale
- Color
- White to light grey
- Luster
- Dull/Earthy
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Physical properties
Hardness: 1 on Mohs scale; Color: White to light grey; Luster: Dull/Earthy; Structure: Fine-grained, porous; Cleavage: None/Conchoidal.
Formation & geological history
Formed in deep marine environments from the accumulation of microscopic skeletal debris (coccoliths) of plankton over millions of years, primarily during the Cretaceous period.
Uses & applications
Used in the manufacturing of cement, lime, quicklime, putty, and as a component in paper, paint, and toothpaste. Historically used for writing boards.
Geological facts
The White Cliffs of Dover are the world's most famous chalk formation. Chalk is actually a form of limestone that is porous and remarkably soft.
Field identification & locations
Identify by its soft, powdery texture and ability to leave a white mark on harder surfaces. It will effervesce (fizz) vigorously when in contact with dilute hydrochloric acid.
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