sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: typically white, gray, or tan; Luster: dull to earthy; Structure: non-crystalline or microcrystalline massive; Cleavage: none in rock form; Specific Gravity: 2.5-2.7

Hardness: 3 on Mohs scale
Color: typically white, gray, or tan
Luster: dull to earthy

Identified February 10, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: typically white, gray, or tan; Luster: dull to earthy; Structure: non-crystalline or microcrystalline massive; Cleavage: none in rock form; Specific Gravity: 2.5-2.7

Formation & geological history

Formed primarily from the accumulation of shell, coral, algal, and fecal debris in warm, shallow marine waters. It can also form through chemical precipitation from lake or ocean water.

Uses & applications

Used extensively in construction as road base, railroad ballast, and an ingredient in cement. It is also used in agriculture to neutralize soil acidity and in the production of lime.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks on Earth. Most of the world's caves are formed in limestone because it is easily dissolved by slightly acidic groundwater.

Field identification & locations

Identify in the field by its softness (can be scratched by a steel nail) and its vigorous reaction (effervescence) when a small amount of dilute hydrochloric acid or strong vinegar is applied. Found globally in ancient seabed deposits.