sedimentary
Limestone
Calcium Carbonate (CaCO3)
Hardness: 3 on Mohs scale; Color: Gray, tan, or white; 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
- Gray, tan, or white
- Luster
- Dull to earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: Gray, tan, or white; 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 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.
Uses & applications
Widely used as a building material, in the manufacture of cement, as an aggregate for the base of roads, as white pigment or filler in products such as toothpaste or paints, and as a soil conditioner.
Geological facts
Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary rock found in karst landscapes, which are characterized by caves and sinkholes.
Field identification & locations
Identify in the field by its softness (can be scratched by a penny) and its effervescence (fizzing) when a drop of dilute hydrochloric acid or strong vinegar is applied. Common worldwide in ancient seabed locations.
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