Rock Identifier
Limestone (Sedimentary rock composed mainly of calcium carbonate (CaCO3)) — sedimentary
sedimentary

Limestone

Sedimentary rock composed mainly of calcium carbonate (CaCO3)

Hardness: 3 on the Mohs scale. Color ranges from white, gray, yellow to brown. Luster is earthy to dull. Crystal structure is typically microcrystalline or composed of skeletal fragments of marine organisms. Cleavage is none, but it has a characteristic conchoidal or uneven fracture.

Hardness
3 on the Mohs scale
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Physical properties

Hardness: 3 on the Mohs scale. Color ranges from white, gray, yellow to brown. Luster is earthy to dull. Crystal structure is typically microcrystalline or composed of skeletal fragments of marine organisms. Cleavage is none, but it has a characteristic conchoidal or uneven fracture.

Formation & geological history

Formed through the accumulation and compaction of organic remains such as shells, coral, and algal debris, or through the chemical precipitation of calcium carbonate from water in shallow marine environments over millions of years.

Uses & applications

Extensively used in the construction industry as building material, crushed stone for road base, a primary component in the manufacture of Portland cement, and in agriculture for neutralizing acidic soils.

Geological facts

Limestone frequently contains fossils of ancient marine life. Famous architectural structures like the Great Pyramids of Giza and the Empire State Building (used in its construction materials) incorporate limestone.

Field identification & locations

Can be easily identified in the field by its characteristic effervescence (fizzing) when a drop of weak hydrochloric acid or vinegar is applied due to the release of carbon dioxide gas. Found worldwide in sedimentary basins.

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