sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Gray, tan, or white; Luster: Dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific gravity: 2.7

Hardness: 3 on Mohs scale
Color: Gray, tan, or white
Luster: Dull to earthy

Identified June 2, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Gray, tan, or white; Luster: Dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific gravity: 2.7

Formation & geological history

Formed in marine environments from the accumulation of coral, shells, and algal debris or by precipitation from calcium-rich waters. Most deposits range from the Paleozoic to the Cenozoic era.

Uses & applications

Primary source of lime and cement for construction; used as a building stone, road base, 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 host rock for most of the world\'s cave systems due to its solubility in slightly acidic rainwater.

Field identification & locations

Identify in the field by its reaction to dilute hydrochloric acid (it fizzes). Commonly found in areas that were once prehistoric shallow seabeds. Collectors look for fossil inclusions.