sedimentary

Limestone (River or Sea Cobble)

Calcium Carbonate (CaCO3)

AI-generated identification · may be incorrect

Hardness: 3 on Mohs scale; Color: Gray to bluish-gray; Luster: Dull to earthy; Texture: Fine-grained with evidence of weathering and organic growth; Cleavage: None (conchoidal fracture).

Hardness: 3 on Mohs scale
Color: Gray to bluish-gray
Luster: Dull to earthy

Identified June 26, 2026More sedimentary →

Explore Limestone (River or Sea Cobble) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 3 on Mohs scale; Color: Gray to bluish-gray; Luster: Dull to earthy; Texture: Fine-grained with evidence of weathering and organic growth; Cleavage: None (conchoidal fracture).

Formation & geological history

Formed through the accumulation of shell, coral, algal, and fecal debris in marine environments. This specimen has been rounded by mechanical erosion in a high-energy water environment, likely coastal or fluvial.

Uses & applications

Primary source of lime for cement, decorative gravel, rip-rap for erosion control, and high-purity limestone is used in glass making.

Geological facts

Limestone often contains fossils of ancient marine life. Because it is carbonate-based, it will effervesce (fizz) when in contact with a weak acid like vinegar.

Field identification & locations

Identify in the field by its softness relative to steel and its reaction to acid. Commonly found near ancient or active sea beds and mountain ranges that were once submerged.