sedimentary
Limestone
Calcium Carbonate (CaCO3)
Hardness: 3-4 (Mohs), Color: White, cream, or light grey, Luster: Dull to earthy, Structure: Fine-grained to massive, Cleavage: None (conchoidal fracture), Specific Gravity: 2.5-2.7
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Physical properties
Hardness: 3-4 (Mohs), Color: White, cream, or light grey, Luster: Dull to earthy, Structure: Fine-grained to massive, Cleavage: None (conchoidal fracture), Specific Gravity: 2.5-2.7
Formation & geological history
Formed primarily from the accumulation of shell, coral, algal, and fecal debris in marine environments. Can also form through precipitation from calcium-rich water in caves or hot springs. Geological ages vary from Precambrian to Holocene.
Uses & applications
Extensively used in construction (building stone, concrete aggregate), cement manufacturing, soil neutralized in agriculture, and as a refinery for steel and glass.
Geological facts
Limestone makes up about 10% of the total volume of all sedimentary rocks. Many of the world's most famous caves, including Mammoth Cave in Kentucky, are carved into limestone by acidic water.
Field identification & locations
Identifiable in the field by hissing/fizzing when a drop of diluted hydrochloric acid is applied (effervescence). Often contains visible fossils of marine organisms. Commonly found in former seabed locations.
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