sedimentary

Limestone

Sedimentary Calcium Carbonate (CaCO3)

Hardness: 3-4 (Mohs scale); Color: light gray to tan; Luster: dull/earthy; Texture: fine-grained to clastic; Often reacts with dilute hydrochloric acid.

Hardness: 3-4 (Mohs scale)
Color: light gray to tan
Luster: dull/earthy

Identified July 4, 2026More sedimentary →

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Physical properties

Hardness: 3-4 (Mohs scale); Color: light gray to tan; Luster: dull/earthy; Texture: fine-grained to clastic; Often reacts with dilute hydrochloric acid.

Formation & geological history

Formed primarily from the accumulation of shell, coral, algal, and fecal debris in clear, warm, shallow marine waters. It can also form chemically through the precipitation of calcium carbonate.

Uses & applications

Extensively used as a building material, aggregate for concrete, manufacturing of cement, and in the production of lime for soil treatment.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is also the primary material where most caves and sinkholes are formed due to its solubility in acidic rainwater.

Field identification & locations

Can be identified in the field by its softness (scratched by a copper coin) and vigorous bubbling when exposed to weak acid like vinegar or lemon juice. Common in ancient reef beds.