sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: typically white, gray, or tan; Luster: dull to earthy; Structure: massive or bedded granular; Cleavage: rhombohedral (in calcite crystals); Specific Gravity: 2.5-2.7

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

Identified May 21, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: typically white, gray, or tan; Luster: dull to earthy; Structure: massive or bedded granular; Cleavage: rhombohedral (in calcite crystals); Specific Gravity: 2.5-2.7

Formation & geological history

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

Uses & applications

Extensively used as a building material, in the manufacture of cement, as an aggregate for the base of roads, as white pigment or filler in products such as toothpaste or paints, and as a soil conditioner.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. Most caves are formed in limestone bedrock through the dissolution of the rock by slightly acidic groundwater.

Field identification & locations

Identify in the field by its softness (can be scratched by a penny/knife) and its strong reaction (effervescence) when touched with a drop of dilute hydrochloric acid or strong vinegar. Found globally in ancient seabed deposits.