sedimentary
Limestone
Calcium Carbonate (CaCO3)
Hardness: 3 on Mohs scale; Color: Gray, tan, or white; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: Perfect rhombohedral (in calcite crystals); Specific Gravity: 2.5-2.7
- Hardness
- 3 on Mohs scale
- Color
- Gray, tan, or white
- Luster
- Dull to earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: Gray, tan, or white; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: Perfect rhombohedral (in calcite crystals); Specific Gravity: 2.5-2.7
Formation & geological history
Formed primarily in marine environments from the accumulation of shell, coral, algal, and fecal debris. It can also form through chemical precipitation from ocean water or groundwater.
Uses & applications
Used extensively in construction (road base, concrete), as a flux in steel making, in the production of lime and cement, and in agriculture to neutralize soil acidity.
Geological facts
Limestone covers about 10% of the Earth's total land surface. It is the primary rock found in karst landscapes, where it dissolves to form extensive cave systems.
Field identification & locations
Identify in the field by its softness (can be scratched by a steel nail) and its strong effervescence (fizzing) when a drop of dilute hydrochloric acid or vinegar is applied. Commonly found in ancient sea beds and river valleys.
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