sedimentary
Limestone
Calcium carbonate (CaCO3)
AI-generated identification · may be incorrectHardness: 3 on Mohs scale; Color: light grey to cream; Luster: dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: rhombohedral (rarely visible in hand sample); Specific gravity: 2.3–2.7
- Hardness
- 3 on Mohs scale
- Color
- light grey to cream
- Luster
- dull to earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: light grey to cream; Luster: dull to earthy; Crystal structure: Trigonal (microcrystalline); Cleavage: rhombohedral (rarely visible in hand sample); Specific gravity: 2.3–2.7
Formation & geological history
Formed primarily from the accumulation of shell, coral, algal, and fecal debris in warm, shallow marine waters. Can also form through precipitation from calcium-rich water.
Uses & applications
Major use in construction as aggregate, manufacture of cement, soil conditioner in agriculture, and as a flux in steel making.
Geological facts
Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary source for karst landscapes, creating massive cave systems and sinkholes through acidity in rainwater.
Field identification & locations
Identify in the field using the 'acid test'—it will fizz (effervesce) when a small drop of diluted hydrochloric acid is applied. Commonly found in areas with past or present marine environments.
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