sedimentary

Grey Limestone Pebble

Limestone (Calcium Carbonate - CaCO3)

AI-generated identification · may be incorrect

Hardness: 3-4 (Mohs scale); Color: light to medium grey; Luster: dull to earthy; Structure: fine-grained, microcrystalline; Cleavage: none (fractures irregularly); Specific gravity: 2.5-2.7

Hardness: 3-4 (Mohs scale)
Color: light to medium grey
Luster: dull to earthy

Identified March 7, 2026More sedimentary →

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Physical properties

Hardness: 3-4 (Mohs scale); Color: light to medium grey; Luster: dull to earthy; Structure: fine-grained, microcrystalline; Cleavage: none (fractures irregularly); Specific gravity: 2.5-2.7

Formation & geological history

Formed through the accumulation of shell, coral, algal, and fecal debris in marine environments. This specific specimen has been water-worn into a smooth pebble by river or coastal erosion. Common in geological formations from the Paleozoic to Mesozoic eras.

Uses & applications

Primary source of lime and cement for construction; used as aggregate for roads, flux in steel production, and as an agricultural soil conditioner. Smaller pebbles are often used in decorative landscaping.

Geological facts

Limestone covers about 10% of the total surface of the Earth's land. It is the primary rock type in which most of the world's caves are formed through the dissolution of the rock by slightly acidic groundwater.

Field identification & locations

Can be identified in the field by its light grey color and its reaction to dilute hydrochloric acid (it will fizz). Commonly found in riverbeds, beaches, and quarries. Collectors look for versions containing visible fossils.