sedimentary
Chalk
Calcium Carbonate (CaCO3) - Biogenic Limestone
Hardness: 1-3 on Mohs scale; Color: White to off-white; Luster: Dull, earthy; Crystal structure: Trigonal (microscopic); Cleavage: None; Specific Gravity: 2.3-2.6
- Hardness
- 1-3 on Mohs scale
- Color
- White to off-white
- Luster
- Dull, earthy
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Physical properties
Hardness: 1-3 on Mohs scale; Color: White to off-white; Luster: Dull, earthy; Crystal structure: Trigonal (microscopic); Cleavage: None; Specific Gravity: 2.3-2.6
Formation & geological history
Formed in deep marine environments from the accumulation of microscopic skeletal remains of plankton (coccolithophores). Most deposits date to the Cretaceous period.
Uses & applications
Used in agriculture for soil treatment, as a building material (whitewash), in cement manufacturing, and traditionally as a drawing/writing tool.
Geological facts
The word 'Cretaceous' comes from 'creta', the Latin word for chalk. The White Cliffs of Dover are the most famous example of chalk formations.
Field identification & locations
Identify by its soft, powdery texture, ability to mark surfaces, and strong effervescence (bubbling) when exposed to weak acid. Found in coastal regions and former ocean beds.
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