sedimentary
Limestone
Calcium Carbonate (CaCO3)
Hardness: 3 on Mohs scale; Color: Light gray to white; Luster: Dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral (on a microscopic level); Specific gravity: 2.5–2.7.
- Hardness
- 3 on Mohs scale
- Color
- Light gray to white
- Luster
- Dull to earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: Light gray to white; Luster: Dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral (on a microscopic level); 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 be formed by the chemical precipitation of calcium carbonate from lake or ocean water.
Uses & applications
Used extensively in construction (as aggregate and building stone), cement production, as a soil conditioner in agriculture, and as a flux in glass and steel manufacturing.
Geological facts
Limestone makes up about 10% of the total volume of all sedimentary rocks. Most caves are formed by the dissolution of limestone by acidic groundwater.
Field identification & locations
Identify in the field by its light color and typical reaction to dilute hydrochloric acid (it will fizz). Look for fossil remains or shell fragments within the matrix.
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