sedimentary
Chalk
Micrite (primarily Calcium Carbonate or CaCO3)
Hardness: 1-3 on Mohs scale; Color: White to grey/buff; Luster: Dull/Earthy; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.3-2.6
- Hardness
- 1-3 on Mohs scale
- Color
- White to grey/buff
- Luster
- Dull/Earthy
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Physical properties
Hardness: 1-3 on Mohs scale; Color: White to grey/buff; Luster: Dull/Earthy; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.3-2.6
Formation & geological history
Formed from the accumulation of microscopic marine organisms like coccolithophores on the ocean floor, primarily during the Cretaceous period.
Uses & applications
Used in the manufacturing of cement, lime, fertilizer, blackboard chalk, and as a whitener in toothpaste and paper production.
Geological facts
The famous White Cliffs of Dover in England are made almost entirely of chalk, consisting of trillions of microscopic skeletons from marine algae.
Field identification & locations
Identify by its soft, powdery texture and high reactivity to cold dilute hydrochloric acid (it will fizz strongly). Found in deep marine depositional environments worldwide.
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