sedimentary
Limestone
Sedimentary rock composed primarily of Calcium Carbonate (CaCO3)
Hardness: 3 on Mohs scale; Color: typically light gray, tan, or white; Luster: dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific gravity: 2.5-2.7
- Hardness
- 3 on Mohs scale
- Color
- typically light gray, tan, or white
- Luster
- dull to earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: typically light gray, tan, or white; Luster: dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; 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 form through chemical precipitation from ocean water or cave environments. Ages range from Precambrian to Holocene.
Uses & applications
Extensively used in construction as an aggregate for road base and railroad ballast, in the production of cement and lime, and as an architectural stone. Used in agriculture to neutralize acidic soils and in the glass-making industry.
Geological facts
Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary parent material for karst topography, which features caves, sinkholes, and underground rivers. Many famous landmarks like the Great Pyramids are built from it.
Field identification & locations
Identify in the field by its reaction to dilute hydrochloric acid (it will fizz/effervesce). Look for fossils, fine grains, and light colors. Common in regions that were once under ancient shallow seas.
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