sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3-4 (Mohs scale), Color: tan, grey, or white. Luster: dull to earthy. Structure: fine-grained, may contain visible shell fragments or fossils. Specific Gravity: 2.5-2.7. Reacts strongly with dilute hydrochloric acid.

Hardness: 3-4 (Mohs scale), Color: tan, grey, or white
Color: tan, grey, or white
Luster: dull to earthy

Identified July 1, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily in marine environments from the accumulation of shell, coral, algal, and fecal debris. It can also form through chemical precipitation from lake or ocean water. Significant deposits date from the Cambrian to the Cenozoic era.

Uses & applications

Used extensively in construction (aggregate, cement), agriculture (soil conditioner), and as a chemical feedstock for producing lime 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, such as Mammoth Cave in the USA, are formed within limestone layers through dissolution by acidic groundwater.

Field identification & locations

Identify in the field by its light color and the 'fizz' test using an acid. It is often found in bedded layers and is a common source of fossil discoveries. Highly common globally.