sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Grey, beige, tan, off-white; Luster: Dull to earthy; Texture: Fine-grained to medium-grained; Reacts strongly with dilute hydrochloric acid (fizzes).

Hardness: 3 on Mohs scale
Color: Grey, beige, tan, off-white
Luster: Dull to earthy

Identified July 23, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Grey, beige, tan, off-white; Luster: Dull to earthy; Texture: Fine-grained to medium-grained; Reacts strongly with dilute hydrochloric acid (fizzes).

Formation & geological history

Formed in warm, shallow marine environments from the accumulation of organic debris such as shell fragments, coral, and algal material, or through direct chemical precipitation of calcium carbonate.

Uses & applications

Used widely in construction as crushed stone for road bases, aggregate in concrete, dimension stone, production of lime and cement, soil conditioner in agriculture, and neutralizer in chemical processes.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. Karst landscapes featuring caves, sinkholes, and underground rivers typically form in limestone due to its solubility in acidic water.

Field identification & locations

Look for light grey to brownish color, fine-grained texture, soft surface easily scratched by a steel blade, and effervescence when exposed to a mild acid like vinegar.