sedimentary

Limestone

CaCO3 (Mainly Calcite or Aragonite)

Hardness: 3 on Mohs scale; Color: Tan, gray, or off-white; Luster: Dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral (on micro-scale); Specific gravity: 2.5 - 2.7.

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

Identified April 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in marine environments through the accumulation of shell, coral, algal, and fecal debris. It can also be formed by the precipitation of calcium carbonate from lake or ocean water.

Uses & applications

Used extensively in construction (road base, concrete, railroad ballast), as a source of lime for agriculture, and in the manufacturing of cement, glass, and steel.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. Many limestone formations contain fossils, which provide important data about Earth's biological history.

Field identification & locations

Identify in the field by its light color and the 'fizz test' (effervesces when exposed to weak acid like vinegar). Often found in layered beds or outcrops in areas that were once prehistoric seafloors.