sedimentary
Limestone
Limestone (Calcium Carbonate - CaCO3)
Hardness: 3 on Mohs scale; Color: Grey, off-white, or tan; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: None/conchoidal fracture; Specific gravity: 2.5–2.7
- Hardness
- 3 on Mohs scale
- Color
- Grey, off-white, or tan
- Luster
- Dull to earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: Grey, off-white, or tan; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: None/conchoidal fracture; Specific gravity: 2.5–2.7
Formation & geological history
Formed primarily in marine environments through the accumulation of shell, coral, algal, and fecal debris. It can also form chemically through the precipitation of calcium carbonate from lake or ocean water.
Uses & applications
Used extensively in construction as road base, railroad ballast, and aggregate in concrete. It is a primary ingredient in Portland cement and used in the steel and chemical industries.
Geological facts
Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary rock type found in Karst landscapes, where it dissolves to form massive cave systems.
Field identification & locations
Identify in the field by its tendency to fizz (effervesce) when a drop of dilute hydrochloric acid (or strong vinegar) is applied. It is common in areas that were once ancient sea beds.
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