sedimentary
Limestone
Calcium Carbonate (CaCO3)
Hardness: 3 on Mohs scale; Color: Gray, tan, or white; Luster: Dull to earthy; Crystal Structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral in calcite crystals; Specific Gravity: 2.5–2.73
- Hardness
- 3 on Mohs scale
- Color
- Gray, tan, or white
- Luster
- Dull to earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: Gray, tan, or white; Luster: Dull to earthy; Crystal Structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral in calcite crystals; Specific Gravity: 2.5–2.73
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 lake or ocean water (evaporites). Most date from various eras, including the Paleozoic and Mesozoic.
Uses & applications
Extensively used in construction (aggregate, cement), as a building stone, in agriculture to neutralize soil acidity, and in the production of glass and steel.
Geological facts
Limestone contains about 10% of the total volume of all sedimentary rocks. It is the primary rock type found in vast karst landscapes and often contains well-preserved fossils of ancient marine life.
Field identification & locations
Identify in the field by its soft texture (scratchable by a copper penny) and its strong effervescent reaction when exposed to cold dilute hydrochloric acid. Commonly found in quarries, road cuts, and coastal cliffs.
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