sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 (Mohs scale); Color: White, grey, or tan; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: Perfect rhombohedral (in calcite crystals, not evident in massive form); Specific Gravity: 2.71

Hardness: 3 (Mohs scale)
Color: White, grey, or tan
Luster: Dull to earthy

Identified July 9, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily in marine environments from the accumulation of shell, coral, algal, and fecal debris. It can also be precipitated from calcium-rich water in caves or springs. Most limestone dates from the Paleozoic to the Cenozoic era.

Uses & applications

Extensively used as a building material, in the manufacture of cement (Portland cement), as an aggregate for road bases, and in the production of lime. It is also used as a flux in steel making.

Geological facts

Limestone occupies about 10% of the total volume of all sedimentary rocks. It is the primary component of most cave systems across the globe due to its solubility in even slightly acidic water.

Field identification & locations

Identify in the field by its softness (it can be scratched by a copper coin) and its effervescence (bubbles) when a drop of diluted hydrochloric acid or strong vinegar is applied. Commonly found in coastal areas and riverbeds.