sedimentary

Limestone (River Pebble)

Calcite (Calcium Carbonate) - CaCO3

Hardness: 3 on Mohs scale; Color: Greyish-tan to light grey; Luster: Dull/Earthy; Structure: Clastic or chemical sedimentary; Cleavage: Perfect rhombohedral in crystal form, but absent in fine-grained rock; Specific Gravity: 2.7

Hardness: 3 on Mohs scale
Color: Greyish-tan to light grey
Luster: Dull/Earthy

Identified July 10, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in shallow marine environments from the accumulation of shell, coral, algal, and fecal debris. It can also be formed by the precipitation of calcium carbonate from lake or ocean water. This specimen has been rounded and smoothed by water erosion in a river or coastal environment.

Uses & applications

Used primarily in the construction industry as crushed stone for road base, in the production of lime and cement, and in agriculture to neutralize soil acidity.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary material found in karst landscapes, leading to the formation of many of the world's most famous cave systems.

Field identification & locations

Can be identified in the field by its softness (it can be scratched by a steel knife) and its reaction to cold dilute hydrochloric acid (effervescence). Often found in riverbeds, cliffs, and quarries.

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