sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3-4 on Mohs scale. Color: white, gray, buff. Luster: dull to earthy. Crystal structure: finely crystalline or massive. Cleavage: generally indistinct. Specific gravity: 2.3-2.7. Often contains fossils. Effervesces in dilute hydrochloric acid.

Hardness: 3-4 on Mohs scale
Color: white, gray, buff
Luster: dull to earthy

Identified May 31, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in shallow marine environments from the accumulation of calcium carbonate skeletal remains (shells, coral, algal debris) over millions of years, later lithified into rock. Common globally.

Uses & applications

Widely used as building material, crushed base for roads, ingredient in concrete, soil conditioner (aglime), and in industrial processes like smelting.

Geological facts

Limestone landscapes often develop into karst topography, featuring caves, sinkholes, and underground rivers. The Great Pyramids of Giza were largely built with limestone blocks.

Field identification & locations

Identified in the field by its pale color, relatively low hardness (can often be scratched by a nail), and effervescence with weak acid. Commonly found in areas that were historically ancient sea beds. Relatively little collector value unless containing significant or well-preserved fossils.