sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: typically grey, white, or tan; Luster: dull to earthy; Crystal Structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific Gravity: 2.7.

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

Identified April 11, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: typically grey, white, or tan; Luster: dull to earthy; Crystal Structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific Gravity: 2.7.

Formation & geological history

Formed primarily by the accumulation of shell, coral, algal, and fecal debris in warm, shallow marine waters. Can also form through precipitation from calcium-rich water. Common in many geological eras from Paleozoic to Cenozoic.

Uses & applications

Used extensively in construction (road base, concrete, building stone), agriculture (lime to neutralize soil), and as a flux in steel making. Also used in glass making and as a white pigment.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks on Earth. It is the primary rock type found in karst landscapes, leading to the formation of spectacular caves and sinkholes.

Field identification & locations

Identify in the field by its tendency to fizz (effervesce) when a drop of dilute hydrochloric acid is applied. Look for visible fossils of marine organisms. Commonly found in areas that were once ancient sea beds.