sedimentary

Chalk

Calcium Carbonate (CaCO3) - Biogenic Limestone

AI-generated identification · may be incorrect

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

Identified May 27, 2026More sedimentary →

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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.