sedimentary
Limestone
Calcium Carbonate (CaCO3)
Hardness: 3 (Mohs scale); Color: light gray to tan; Luster: dull to earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: Perfect rhombohedral (rarely visible in hand sample); Specific Gravity: 2.5–2.7
- Hardness
- 3 (Mohs scale)
- Color
- light gray to tan
- Luster
- dull to earthy
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Physical properties
Hardness: 3 (Mohs scale); Color: light gray to tan; Luster: dull to earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: Perfect rhombohedral (rarely visible in hand sample); Specific Gravity: 2.5–2.7
Formation & geological history
Formed 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 primarily in construction as road base, railroad ballast, and concrete aggregate; also used in the production of cement, glass making, and agricultural lime.
Geological facts
Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary rock type in karst landscapes, where its solubility leads to the formation of caves and sinkholes.
Field identification & locations
Can be identified in the field by its reaction to dilute hydrochloric acid (it fizzes). Look for fossils of marine organisms or a fine-grained, light-colored appearance in outcrops.
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