sedimentary
Limestone (with crushed gravel)
Limestone (Calcium Carbonate, CaCO3)
Mohs hardness 3, earthy to dull luster, buff to tan/yellowish color with grey crushed gravel, fine-grained microcrystalline structure, effervesces strongly in dilute hydrochloric acid
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Physical properties
Mohs hardness 3, earthy to dull luster, buff to tan/yellowish color with grey crushed gravel, fine-grained microcrystalline structure, effervesces strongly in dilute hydrochloric acid
Formation & geological history
Formed in shallow, warm marine environments by the accumulation of organic debris like coral, shells, algae, and precipitation of calcium carbonate over millions of years
Uses & applications
Widely used as construction aggregate, crushed stone for driveways and road beds, cement production, soil conditioner (agricultural lime), and building material
Geological facts
Limestone makes up about 10% of the total volume of all sedimentary rocks on Earth. Acidic groundwater can dissolve limestone to form vast subterranean cave systems and karst topography.
Field identification & locations
Identified by its softness (can be scratched by a steel nail), dull earthy texture, reaction to acid, and association with sedimentary layers or construction gravel
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