sedimentary
Limestone
Calcium Carbonate (CaCO3)
Hardness: 3-4 (Mohs), Color: Light gray to tan, Luster: Dull/Earthy, Crystal Structure: Trigonal (microcrystalline), Cleavage: Perfect rhombohedral but usually not visible in hand samples, Specific Gravity: 2.5-2.7
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Physical properties
Hardness: 3-4 (Mohs), Color: Light gray to tan, Luster: Dull/Earthy, Crystal Structure: Trigonal (microcrystalline), Cleavage: Perfect rhombohedral but usually not visible in hand samples, 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 water or cave water. Ages range from Precambrian to Holocene.
Uses & applications
Extensively used as a building material, aggregate for concrete and asphalt, raw material for cement, soil conditioner in agriculture, and in the manufacturing of glass and steel.
Geological facts
Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary rock type found in karst landscapes, resulting in spectacular caves and sinkholes due to its solubility in acidic water.
Field identification & locations
Can be identified in the field by its softness (scratched by a copper penny or steel knife) and its diagnostic reaction to dilute hydrochloric acid, which causes it to effervesce (fizz).
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