sedimentary
Limestone
Calcium Carbonate (CaCO3)
Hardness: 3 on Mohs scale; Color: Grey, tan, or white; Luster: Dull/earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: Perfect rhombohedral (rarely visible in bulk sample); Specific Gravity: 2.5-2.7
- Hardness
- 3 on Mohs scale
- Color
- Grey, tan, or white
- Luster
- Dull/earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: Grey, tan, or white; Luster: Dull/earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: Perfect rhombohedral (rarely visible in bulk sample); Specific Gravity: 2.5-2.7
Formation & geological history
Formed primarily from the accumulation of shell, coral, algal, and fecal debris in marine environments. Can also form through the precipitation of calcium carbonate from lake or ocean water.
Uses & applications
Extensively used in construction as an aggregate, cement production, architectural stone, soil conditioner in agriculture, and for neutralizing acidic gases.
Geological facts
Limestone is the primary source of the world's lime. It often contains abundant fossils such as crinoids and brachiopods. Many of the world's most famous caves are formed in limestone via dissolution.
Field identification & locations
Identify in the field using the 'acid test'—it fizzes vigorously when exposed to dilute hydrochloric acid. It is often found in bedded layers or massive outcrops in regions that were once ancient sea beds.
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