sedimentary

Limestone

Calcite-rich sedimentary rock (CaCO3)

Hardness: 3 on Mohs scale; Color: Cream, tan, or grey; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline calcite); Cleavage: Perfect rhombohedral in calcite crystals, but usually massive or granular in rock form; Specific gravity: 2.5-2.7

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

Identified June 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of shell, coral, algal, and fecal debris in warm, shallow marine waters. It can also form through chemical precipitation from calcium carbonate-rich water in caves or springs.

Uses & applications

Extensively used in construction as building blocks, floor tiles, and as a primary ingredient in cement and mortar. It is also used as a soil conditioner and in the production of glass.

Geological facts

Limestone covers about 10% of the Earth's land surface. Famous structures like the Great Pyramid of Giza and the Parthenon were constructed primarily from various forms of limestone.

Field identification & locations

Identify in the field by its ease of scratching with a steel blade and a fizzing reaction (effervescence) when a small drop of dilute hydrochloric acid or vinegar is applied. Look for fossil inclusions.