sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: typically grey, white, or tan; Luster: dull to earthy; Crystal Structure: trigonal (when calcite is visible); Cleavage: perfect rhombohedral in calcite crystals; Specific Gravity: 2.5-2.7

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

Identified February 22, 2026More sedimentary →

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Physical properties

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. Geological age can range from Precambrian to Recent.

Uses & applications

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

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary material found in famous karst landscapes and cave systems like Mammoth Cave in the USA. Most fossils are found within limestone layers.

Field identification & locations

Identify in the field by its tendency to fizz (effervesce) when a drop of dilute hydrochloric acid is applied. It often contains visible fossils and occurs in massive beds. Common worldwide, especially in areas that were once prehistoric shallow seas.