sedimentary
Limestone
Calcareous sedimentary rock (CaCO3)
Hardness: 3 on Mohs scale; Color: Grey, tan, or white; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline calcite); Cleavage: None/Irregular; Specific gravity: 2.5–2.7
- Hardness
- 3 on Mohs scale
- Color
- Grey, tan, or white
- Luster
- Dull to earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: Grey, tan, or white; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline calcite); Cleavage: None/Irregular; Specific gravity: 2.5–2.7
Formation & geological history
Formed primarily from the accumulation of shell, coral, algal, and fecal debris in marine environments. It can also form chemically through the precipitation of calcium carbonate from lake or ocean water.
Uses & applications
Extensively used as a building material, aggregate for concrete, a base for roads, and in the production of lime and cement.
Geological facts
Limestone often contains fossils and is the primary rock type found in karst landscapes, which are characterized by caves and sinkholes due to the rock's solubility in rainwater.
Field identification & locations
Identify in the field by its softness (it can be scratched by a knife) and its reaction to dilute hydrochloric acid (it will fizz or effervesce). Commonly found in shallow marine basins.
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