sedimentary
Limestone
Calcium Carbonate (CaCO3)
Hardness: 3 on Mohs scale; Color: typically grey, white, or tan; Luster: dull to earthy; Crystal Structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral in calcite crystals; Specific Gravity: 2.5-2.7
- Hardness
- 3 on Mohs scale
- Color
- typically grey, white, or tan
- Luster
- dull to earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: typically grey, white, or tan; Luster: dull to earthy; Crystal Structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral in calcite crystals; Specific Gravity: 2.5-2.7
Formation & geological history
Formed primarily in marine environments from 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
Extensively used in construction as an aggregate, an ingredient in cement, a soil conditioner in agriculture, and as a decorative stone in architecture.
Geological facts
Limestone makes up about 10% of the total volume of all sedimentary rocks. Most of the world's caves are formed in limestone because it is easily dissolved by acidic groundwater.
Field identification & locations
Identify in the field by its softness (it can be scratched with a penny) and its reaction to dilute hydrochloric acid (it will fizz or effervesce). Commonly found in ancient sea beds and karst landscapes.
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