sedimentary
Limestone (or Calcite Nodules)
Calcium Carbonate (CaCO3)
Hardness: 3 on Mohs scale; Color: Off-white, beige, or pale tan; Luster: Dull to earthy; Cleavage: Perfect rhombohedral in calcite crystals, blocky or irregular in rock form; Specific Gravity: ~2.71
- Hardness
- 3 on Mohs scale
- Color
- Off-white, beige, or pale tan
- Luster
- Dull to earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: Off-white, beige, or pale tan; Luster: Dull to earthy; Cleavage: Perfect rhombohedral in calcite crystals, blocky or irregular in rock form; Specific Gravity: ~2.71
Formation & geological history
Formed primarily in shallow, warm marine environments through the accumulation and compaction of organic debris like shells, coral, and algal remains, or precipitated directly from calcium-rich water.
Uses & applications
Widely used as a primary ingredient in cement and concrete, as a soil conditioner in agriculture, for stone carving, and in water treatment.
Geological facts
Limestone makes up about 10% of the total volume of all sedimentary rocks on Earth. It reacts strongly with dilute acids like vinegar by effervescing (fissing/bubbling) due to the release of carbon dioxide gas.
Field identification & locations
Easily identified by testing with a drop of acid (vinegar) which produces visible carbon dioxide bubbles, or by checking hardness with a steel knife (which easily scratches calcite). Common in karst landscapes and limestone quarries worldwide.
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