sedimentary
Limestone
Calcium Carbonate (CaCO3)
Hardness: 3-4 (Mohs scale), Color: Gray to tan/brown with white calcite veining, Luster: Dull to earthy, Crystal structure: Microcrystalline (micrite), Cleavage: None (conchoidal to irregular fracture)
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Physical properties
Hardness: 3-4 (Mohs scale), Color: Gray to tan/brown with white calcite veining, Luster: Dull to earthy, Crystal structure: Microcrystalline (micrite), Cleavage: None (conchoidal to irregular fracture)
Formation & geological history
Formed primarily from the accumulation of shell, coral, algal, and fecal debris in warm, shallow marine waters. This specific sample shows signs of tectonic stress or weathering with secondary mineral infilling in fractures (veining).
Uses & applications
Widely used as building stone, aggregate for concrete, road base, and raw material for manufacturing cement and lime. Also used in soil neutralization.
Geological facts
Limestone makes up about 10% of the total volume of all sedimentary rocks on Earth. Most of the world's great cave systems are formed in limestone through dissolution by acidic groundwater.
Field identification & locations
Identified by its reaction to dilute hydrochloric acid (it fizzes). In the field, look for a relatively soft rock that exhibits a gray weathered surface and often contains visible fossil fragments or calcite veins. Common globally in karst landscapes.
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