sedimentary

Chalk

Calcium Carbonate (CaCO3)

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

Hardness: 1-3 (Mohs scale)
Color: White to light grey
Luster: Dull, earthy

Identified July 19, 2026More sedimentary →

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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.