sedimentary
Limestone
Calcium Carbonate (CaCO3)
Hardness: 3 on Mohs scale; Color: typically grey, white, or tan; Luster: dull to earthy; Crystal Structure: Trigonal (rhombohedral); Cleavage: Perfect rhombohedral in calcite form; Specific Gravity: 2.71.
- Hardness
- 3 on Mohs scale
- Color
- typically grey, white, or tan
- Luster
- dull to earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: typically grey, white, or tan; Luster: dull to earthy; Crystal Structure: Trigonal (rhombohedral); Cleavage: Perfect rhombohedral in calcite form; Specific Gravity: 2.71.
Formation & geological history
Formed in marine environments from the accumulation of shell, coral, algal, and fecal debris. It can also be formed by the precipitation of calcium carbonate from lake or ocean water.
Uses & applications
Extensively used as a building material, in the manufacture of cement, as an aggregate for the base of roads, in white pigment, and as a soil conditioner.
Geological facts
Limestone makes up about 10% of the total volume of all sedimentary rocks. Many caves are formed in limestone because it is soluble in weak acidic groundwater.
Field identification & locations
Identification in the field is usually done with the 'acid test'—it will effervesce (fizz) when a drop of dilute hydrochloric acid is applied. It is common in ancient sea beds.
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