sedimentary
Limestone (Micrite/Chalky variety)
Calcium Carbonate (CaCO3)
Hardness: 3 on Mohs scale; Color: Cream, tan, or light gray; Luster: Dull/Earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: None (subconchoidal fracture); Specific gravity: 2.3 - 2.7
- Hardness
- 3 on Mohs scale
- Color
- Cream, tan, or light gray
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: Cream, tan, or light gray; Luster: Dull/Earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: None (subconchoidal fracture); Specific gravity: 2.3 - 2.7
Formation & geological history
Formed through the accumulation of shell, coral, algal, and fecal debris in warm, shallow marine waters. It can also form chemically through the precipitation of calcium carbonate from lake or ocean water. Geological age ranges from Precambrian to Holocene.
Uses & applications
Used extensively as an aggregate for the base of roads and railroads, as a component in concrete and cement, as a flux in steel making, and in the production of lime.
Geological facts
Limestone makes up about 10% of the total volume of all sedimentary rocks. Many world-famous caves, such as Mammoth Cave in Kentucky, are formed by the dissolution of limestone by slightly acidic groundwater.
Field identification & locations
Identify in the field by its softness (can be scratched by a copper coin/steel) and its vigorous effervescence (fizzing) when a drop of 10% hydrochloric acid is applied. Commonly found in massive beds in ancient seafloor regions.
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