sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3-4 (Mohs), Color: Light gray/beige, Luster: Dull/Earthy, Crystal Structure: Hexagonal (calcite based), Cleavage: Perfect rhombohedral in calcite crystals but often massive

Identified June 14, 2026More sedimentary →

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Physical properties

Hardness: 3-4 (Mohs), Color: Light gray/beige, Luster: Dull/Earthy, Crystal Structure: Hexagonal (calcite based), Cleavage: Perfect rhombohedral in calcite crystals but often massive

Formation & geological history

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

Uses & applications

Extensively used in construction for road base, aggregate in concrete, production of cement, and 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 many of the world's most famous caves and karst landscapes.

Field identification & locations

Easy to identify in the field using the 'acid test' where it effervesces (fizzes) when a drop of dilute hydrochloric acid (or vinegar) is applied. Found worldwide in ancient seabed deposits.