sedimentary
Chalk
Calcium Carbonate (CaCO3)
AI-generated identification · may be incorrectHardness: 1-3 (Mohs scale); Color: White to light grey; Luster: Dull, earthy; Crystal structure: Trigonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.1-2.9
- Hardness
- 1-3 (Mohs scale)
- Color
- White to light grey
- Luster
- Dull, earthy
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Physical properties
Hardness: 1-3 (Mohs scale); Color: White to light grey; Luster: Dull, earthy; Crystal structure: Trigonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.1-2.9
Formation & geological history
Formed from the accumulation of microscopic marine organisms (coccolithophore skeletons) in deep-sea environments over millions of years, primarily during the Cretaceous Period.
Uses & applications
Used in construction, lime production, agriculture (soil pH correction), blackboard chalk, and as a filler in paper, paint, and plastics.
Geological facts
The White Cliffs of Dover are the most famous example of chalk formations in the world. It is highly porous and will effervesce (fizz) vigorously when in contact with dilute hydrochloric acid.
Field identification & locations
Identify by its white, soft, and powdery feel; it rubs off easily on surfaces. Found in massive beds in England, Western Europe, and parts of North America.
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