sedimentary
Limestone
Calcium Carbonate (CaCO3)
Hardness: 3 (Mohs scale); Color: light grey, white, buff, or tan; Luster: dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific gravity: 2.7.
- Hardness
- 3 (Mohs scale)
- Color
- light grey, white, buff, or tan
- Luster
- dull to earthy
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Physical properties
Hardness: 3 (Mohs scale); Color: light grey, white, buff, or tan; Luster: dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific gravity: 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 groundwater (as in caves).
Uses & applications
Extensively used in construction as an aggregate for road bases and railroad ballast. It is the primary raw material for making cement, used as a soil conditioner in agriculture, and as a flux in steel production.
Geological facts
Limestone occupies about 10% of the total volume of all sedimentary rocks. Landscapes formed by the dissolving of limestone are known as karst topography, famous for complex cave systems and sinkholes.
Field identification & locations
Identify in the field by its soft surface (can be scratched by a copper penny) and its vigorous effervescence when exposed to diluted hydrochloric acid or vinegar. Commonly found in ancient sea beds.
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