sedimentary
Limestone
Sedimentary rock composed primarily of Calcium Carbonate (CaCO3)
Hardness: 3-4 (Mohs scale); Color: White, tan, gray; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline calcite); Cleavage: Rhombohedral (microscopic); Specific gravity: 2.3-2.7
- Hardness
- 3-4 (Mohs scale)
- Color
- White, tan, gray
- Luster
- Dull to earthy
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Physical properties
Hardness: 3-4 (Mohs scale); Color: White, tan, gray; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline calcite); Cleavage: Rhombohedral (microscopic); Specific gravity: 2.3-2.7
Formation & geological history
Formed primarily in marine environments from the accumulation of shell, coral, algal, and fecal debris. It can also be formed by the precipitation of calcium carbonate from lake or ocean water.
Uses & applications
Used extensively in construction as road base, aggregate, and building stone. It is a key ingredient in portland cement and is used as a soil conditioner in agriculture.
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 soluble in slightly acidic groundwater.
Field identification & locations
Can be identified in the field by the 'acid test': it will effervesce (fizz) when a drop of dilute hydrochloric acid is applied. Look for fossil remains which are common in many limestone layers.
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