sedimentary
Limestone (River or Sea Cobble)
Calcium Carbonate (CaCO3)
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
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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.
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