sedimentary
Limestone
Calcium Carbonate (CaCO3)
Hardness: 3-4 (Mohs); Color: Gray, tan, white, or light brown; Luster: Dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Rhombohedral (microscopic); Specific gravity: 2.7
- Hardness
- 3-4 (Mohs)
- Color
- Gray, tan, white, or light brown
- Luster
- Dull to earthy
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Physical properties
Hardness: 3-4 (Mohs); Color: Gray, tan, white, or light brown; Luster: Dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Rhombohedral (microscopic); Specific gravity: 2.7
Formation & geological history
Formed in marine environments through the accumulation of shell, algal, and fecal debris. It can also form via chemical precipitation from calcium-rich water.
Uses & applications
Used extensively in construction as aggregate, in cement production, as a building stone (facing), and in agriculture to neutralize soil acidity.
Geological facts
Limestone often contains well-preserved fossils. It is the primary component of most cave systems through the process of dissolution by slightly acidic groundwater.
Field identification & locations
Identify by testing with a drop of dilute hydrochloric acid; it will effervesce (fizz) vigorously. It is commonly found in sedimentary basins and ancient sea beds worldwide.
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