sedimentary
Limestone
Calcium Carbonate (CaCO3)
Hardness: 3 on Mohs scale; Color: Gray, tan, or white with greenish moss; Luster: Dull to earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: None visible in hand specimen; Specific Gravity: 2.3–2.7.
- Hardness
- 3 on Mohs scale
- Color
- Gray, tan, or white with greenish moss
- Luster
- Dull to earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: Gray, tan, or white with greenish moss; Luster: Dull to earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: None visible in hand specimen; Specific Gravity: 2.3–2.7.
Formation & geological history
Formed primarily from the accumulation of shell, coral, algal, and fecal debris in clear, warm, shallow marine waters. Can also be formed by the precipitation of calcium carbonate from lake or ocean water.
Uses & applications
Used widely in construction (aggregate, cement), agriculture (soil conditioner), and industrial processes (scrubbers, glass making). Occasionally used as a decorative building stone.
Geological facts
Limestone makes up about 10% of the total volume of all sedimentary rocks on Earth. It is the primary rock type in which caves and sinkholes form due to its solubility in slightly acidic water.
Field identification & locations
Identify in the field by its softness (can be scratched by a knife) and its reaction to dilute hydrochloric acid (it will fizz). Look for fossil fragments or a fine-grained, 'stony' appearance.
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