sedimentary
Limestone
Calcium Carbonate (CaCO3)
Hardness: 3 (Mohs scale); Color: Gray, tan, or white; Luster: Dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral in calcite forms; Specific gravity: 2.5-2.7
- Hardness
- 3 (Mohs scale)
- Color
- Gray, tan, or white
- Luster
- Dull to earthy
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Physical properties
Hardness: 3 (Mohs scale); Color: Gray, tan, or white; Luster: Dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral in calcite forms; Specific gravity: 2.5-2.7
Formation & geological history
Formed in marine environments through the accumulation of shell, coral, algal, and fecal debris. It can also be formed by the chemical precipitation of calcium carbonate from lake or ocean water.
Uses & applications
Widely used in construction (concrete), as an aggregate for road bases, in cement manufacturing, and as a soil conditioner in agriculture to neutralize acidity.
Geological facts
Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary rock type found in karst landscapes, which are famous for caves and sinkholes.
Field identification & locations
Identify in the field by applying a drop of dilute hydrochloric acid; it will effervesce (fizz) vigorously. It often contains visible fossils of marine organisms.
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