sedimentary
Chalk
Sedimentary carbonate rock (Calcite, CaCO3)
Hardness: 1 on Mohs scale, Color: White or light grey, Luster: Earthy, Crystal structure: Microcrystalline/amorphous feel, Cleavage: None distinct, Specific gravity: 1.5 - 2.2
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Physical properties
Hardness: 1 on Mohs scale, Color: White or light grey, Luster: Earthy, Crystal structure: Microcrystalline/amorphous feel, Cleavage: None distinct, Specific gravity: 1.5 - 2.2
Formation & geological history
Formed by the accumulation of microscopic calcareous shells (coccoliths) of marine micro-organisms over millions of years during the Cretaceous period.
Uses & applications
Used in agriculture to raise soil pH, in construction for lime and cement, in manufacturing of chalkboards, and historically as a writing implement.
Geological facts
Chalk cliffs, such as the White Cliffs of Dover, formed from deposits laid down during the Cretaceous period when much of Europe was submerged under shallow seas.
Field identification & locations
Easily identified by its soft, earthy texture, white color, and effervescence (fizzing) when exposed to dilute hydrochloric acid. Commonly found in chalk downlands.
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