sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: typically light gray, tan, or white; Luster: dull to earthy; Crystal Structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral (in crystalline form); Specific Gravity: 2.3 to 2.7.

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

Identified March 1, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily through the accumulation of shell, coral, algal, and fecal debris in marine environments. It can also form chemically through the precipitation of calcium carbonate from lake or ocean water. Most specimens date from the Paleozoic era to the present.

Uses & applications

Extensively used as a building material, in the manufacturing of cement and lime, as an aggregate for road bases, and in the production of glass. It is also used 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 karst topographies, where its solubility in water creates spectacular cave systems and sinkholes.

Field identification & locations

Can be identified in the field by its softness (can be scratched by a copper coin) and its effervescence (bubbling) when a drop of dilute hydrochloric acid or strong vinegar is applied. Commonly found in former marine basins and mountain ranges.