sedimentary
Limestone
Calcium Carbonate (CaCO3)
Hardness: 3 on Mohs scale; Color: typically white, gray, or tan; Luster: dull to earthy; Crystal structure: hexagonal-rhombohedral (as calcite); Cleavage: perfect rhombohedral in crystal form; Specific gravity: 2.71
- Hardness
- 3 on Mohs scale
- Color
- typically white, gray, or tan
- Luster
- dull to earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: typically white, gray, or tan; Luster: dull to earthy; Crystal structure: hexagonal-rhombohedral (as calcite); Cleavage: perfect rhombohedral in crystal form; Specific gravity: 2.71
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 (travertine).
Uses & applications
Extensively used in construction as aggregate, road base, and as a component of cement. Also used as a soil conditioner (agricultural lime) and in the production of steel and glass.
Geological facts
Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary host rock for most of the world's cave systems due to its solubility in slightly acidic water.
Field identification & locations
Identify in the field by its softness (can be scratched by a copper penny) and its effervescence (fizzing) when a drop of dilute hydrochloric acid or strong vinegar is applied. Commonly found in areas with past or present marine basins.
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