sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: White, tan, or light grey; Luster: Dull to earthy; Crystal Structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific Gravity: 2.5-2.7

Hardness: 3 on Mohs scale
Color: White, tan, or light grey
Luster: Dull to earthy

Identified July 1, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: White, tan, or light grey; Luster: Dull to earthy; Crystal Structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific Gravity: 2.5-2.7

Formation & geological history

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

Uses & applications

Used extensively in construction as road base, concrete aggregate, and building stone. Ground up as a flux in steel making and for neutralizing acidic soils in gardening.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary material found in most cave systems and is essential for the production of cement and lime.

Field identification & locations

Identify in the field by applying a drop of dilute hydrochloric acid; it will vigorously effervesce (fizz). Commonly found in areas that were once prehistoric seafloors.