sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: White, cream, or gray; Luster: Dull to earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: None/Irregular; Specific Gravity: 2.3-2.7

Hardness: 3 on Mohs scale
Color: White, cream, or gray
Luster: Dull to earthy

Identified March 23, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: White, cream, or gray; Luster: Dull to earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: None/Irregular; Specific Gravity: 2.3-2.7

Formation & geological history

Composed primarily of skeletal fragments of marine organisms such as coral, foraminifera, and mollusks. Formed in clear, warm, shallow marine waters over millions of years through lithification.

Uses & applications

Extensively used in construction as building stone, road base, and aggregate. Also used in the production of lime, cement, and as a soil conditioner in agriculture.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. Most of the world's great cave systems, like Mammoth Cave, are carved out of limestone by acidic groundwater.

Field identification & locations

Can be identified in the field by its white or tan color and its 'fizzing' reaction when exposed to cold dilute hydrochloric acid (or vinegar). Common in areas that were once prehistoric seafloors.