sedimentary

Limestone

Sedimentary rock composed primarily of Calcium Carbonate (CaCO3)

AI-generated identification · may be incorrect

Hardness: 3 on Mohs scale; Color: White, off-white, light gray, or tan; Luster: Dull to earthy; Crystal structure: Usually microcrystalline (calcite); Reacts vigorously with dilute hydrochloric acid.

Hardness: 3 on Mohs scale
Color: White, off-white, light gray, or tan
Luster: Dull to earthy

Identified June 3, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: White, off-white, light gray, or tan; Luster: Dull to earthy; Crystal structure: Usually microcrystalline (calcite); Reacts vigorously with dilute hydrochloric acid.

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 ocean or lake water. Geological age can range from Precambrian to Recent.

Uses & applications

Extensively used as a building material, aggregate for concrete, manufacture of cement, soil conditioner in agriculture, and for neutralizing acid in various industrial processes.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. Most of the world's most famous caves are formed in limestone via dissolution by slightly acidic groundwater.

Field identification & locations

Identify in the field by its light color and the 'fizz test' (effervescence when exposed to acid). It is commonly found in areas that were once prehistoric seafloors. Look for small fossil fragments or shell imprints.