sedimentary
Limestone
Calcium Carbonate (CaCO3)
Hardness: 3 on Mohs scale; Color: Gray, tan, or white; Luster: Dull to earthy; Crystal Structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral in calcite crystals; Specific Gravity: 2.5–2.7
- Hardness
- 3 on Mohs scale
- Color
- Gray, tan, or white
- Luster
- Dull to earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: Gray, tan, or white; Luster: Dull to earthy; Crystal Structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral in calcite crystals; Specific Gravity: 2.5–2.7
Formation & geological history
Primarily formed in marine environments by the accumulation of shell, coral, algal, and fecal debris. It can also form through chemical precipitation from calcium-rich waters. Geological ages range from Precambrian to Holocene.
Uses & applications
Extensively used as a building material (cut stone), aggregate for road bases, a primary ingredient in Portland cement, and in agriculture to neutralize acidic soils.
Geological facts
Limestone accounts for about 10% of the total volume of all sedimentary rocks. Most of the world’s spectacular caves and caverns are formed within limestone beds through the dissolution by slightly acidic groundwater.
Field identification & locations
Identify in the field by its reaction (fizzing) when a drop of dilute hydrochloric acid is applied. It is commonly found in karst landscapes and mountain ranges that were once ancient sea floors. Collectors look for fossilized inclusions.
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