sedimentary
Limestone Pebble
Calcium Carbonate (CaCO3)
Mohs hardness of 3, dull to earthy luster, light tan to cream color with subtle brownish iron staining, microcrystalline to fine-grained texture, and effervesces strongly in dilute hydrochloric acid.
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Physical properties
Mohs hardness of 3, dull to earthy luster, light tan to cream color with subtle brownish iron staining, microcrystalline to fine-grained texture, and effervesces strongly in dilute hydrochloric acid.
Formation & geological history
Formed in shallow, warm marine environment through the accumulation and compaction of chemical precipitates and shell fragments. Often displays weathering features such as small dissolution pits.
Uses & applications
Limestone is extensively used in construction aggregate, cement manufacture, soil conditioning in agriculture, and as a lime flux in steelmaking. Small weathered pebbles are often collected as curious natural rocks.
Geological facts
Limestone makes up about 10% of the total volume of all sedimentary rocks. Over geological time, groundwater slowly dissolves limestone, creating karst landscapes, sinkholes, and elaborate cave systems.
Field identification & locations
Identified in the field by its light cream or tan color, relative softness (scratched easily by a steel nail), dull surface finish, and diagnostic fizzing reaction when exposed to dilute acid. Common in ancient ocean basin regions and river beds worldwide.
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