sedimentary
Limestone
Sedimentary rock composed of Calcium Carbonate (CaCO3)
Hardness: 3 on Mohs scale; Color: Grey, tan, or white; Luster: Dull to earthy; Structure: Microcrystalline or clastic; Cleavage: None (conchoidal fracture possible); Specific Gravity: 2.3–2.7
- Hardness
- 3 on Mohs scale
- Color
- Grey, tan, or white
- Luster
- Dull to earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: Grey, tan, or white; Luster: Dull to earthy; Structure: Microcrystalline or clastic; Cleavage: None (conchoidal fracture possible); Specific Gravity: 2.3–2.7
Formation & geological history
Formed primarily from the accumulation of shell, coral, algal, and fecal debris in marine environments. It can also form through chemical precipitation from ocean or lake water. Common in basins globally spanning hundreds of millions of years.
Uses & applications
Used extensively in construction as road base, aggregate for concrete, production of cement, and as a soil conditioner in agriculture. High-grade specimens are used in architectural cladding.
Geological facts
Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary source of lime for the steel and chemical industries. Most caves are formed by the dissolution of limestone by acidic groundwater.
Field identification & locations
Can be identified in the field by its softness (scratched by a steel blade) and its distinct effervescence (bubbling) when a drop of weak hydrochloric acid or vinegar is applied. Commonly found in former marine basins.
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