sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Gray, tan, white, or light brown; Luster: Dull/Earthy; Crystal Structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral in calcite crystals; Specific Gravity: 2.5–2.7

Hardness: 3 on Mohs scale
Color: Gray, tan, white, or light brown
Luster: Dull/Earthy

Identified March 16, 2026More sedimentary →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed primarily in shallow, warm marine waters from the accumulation of coral, shell, and algal debris (biochemical) or through chemical precipitation from calcium-rich water. It is found in stratigraphic sequences dating from the Precambrian to the present.

Uses & applications

Extensively used in construction as an aggregate, a key ingredient in cement/concrete, a flux in metal smelting, and a soil conditioner in agriculture. Pure forms are used in paper-making and cosmetics. It is also a popular building stone.

Geological facts

Limestone accounts for about 10% of the total volume of all sedimentary rocks. It is the primary host rock for most of the world's karst landscapes and cave systems due to its high solubility in acidic water.

Field identification & locations

Identify in the field by applying a dilute acid (like vinegar); it will effervesce (fizz) as it releases CO2. It is often found in bedded layers or cliffs near former oceanic environments. Collectors look for limestone containing visible fossils or 'vugs' with secondary mineral growth like calcite or quartz.