sedimentary
Limestone
Sedimentary rock composed of Calcium Carbonate (CaCO3)
Hardness: 3 (Mohs scale); Color: Gray to light tan with orange weathering crust; Luster: Dull/Earthy; Structure: Fine-grained, microcrystalline; Cleavage: None (conchoidal to irregular fracture).
- Hardness
- 3 (Mohs scale)
- Color
- Gray to light tan with orange weathering crust
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3 (Mohs scale); Color: Gray to light tan with orange weathering crust; Luster: Dull/Earthy; Structure: Fine-grained, microcrystalline; Cleavage: None (conchoidal to irregular fracture).
Formation & geological history
Formed by the accumulation of shell, coral, algal, and fecal debris in marine environments, or via chemical precipitation. This specific specimen shows weathering of iron minerals, creating the orange exterior.
Uses & applications
Primary source of lime for cement, used as a building stone, road base, and in agricultural soil treatment to neutralize acidity.
Geological facts
Limestone makes up about 10% of the total volume of all sedimentary rocks. It is essential for the formation of caves and karst landscapes due to its solubility in slightly acidic water.
Field identification & locations
Identified in the field by its gray color and strong bubbling reaction when exposed to dilute hydrochloric acid. It often contains visible fossils. Common in historically submerged oceanic plates.
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