sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: Gray, tan, or beige; Luster: Dull to earthy; Structure: Clastic or non-clastic grain texture; Cleavage: None; Specific Gravity: 2.5–2.7

Hardness: 3 on Mohs scale
Color: Gray, tan, or beige
Luster: Dull to earthy

Identified July 16, 2026More sedimentary →

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Physical properties

Hardness: 3 on Mohs scale; Color: Gray, tan, or beige; Luster: Dull to earthy; Structure: Clastic or non-clastic grain texture; Cleavage: None; Specific Gravity: 2.5–2.7

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 through the precipitation of calcium carbonate from lake or ocean water.

Uses & applications

Used widely in construction as a road base, railroad ballast, and aggregate in concrete. It is also the primary ingredient in Portland cement and used in soil treatment to neutralize acidity.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It often contains visible fossils, offering a glimpse into ancient marine life.

Field identification & locations

Can be identified in the field by its effervescence (fizzing) when a drop of dilute hydrochloric acid or vinegar is applied. It is common in regions that were once covered by shallow seas.