sedimentary

Limestone Pebble

Limestone (Calcium Carbonate, CaCO3)

AI-generated identification · may be incorrect

Hardness: 3-4 (Mohs scale); Color: Gray to tan; Luster: Dull/Earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: None/Irregular

Hardness: 3-4 (Mohs scale)
Color: Gray to tan
Luster: Dull/Earthy

Identified June 2, 2026More sedimentary →

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Physical properties

Hardness: 3-4 (Mohs scale); Color: Gray to tan; Luster: Dull/Earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: None/Irregular

Formation & geological history

Formed primarily from the accumulation of shell, coral, algal, and fecal debris in marine environments. It can also form through chemical precipitation from lake or ocean water.

Uses & applications

Used extensively in construction as road base, railroad ballast, and an ingredient in cement. Finer grades are used in agriculture and as industrial filler.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks on Earth. It is the primary source of 'karst' topography, which includes caves and sinkholes.

Field identification & locations

Can be identified in the field by its tendency to fizz when a small amount of dilute acid (like vinegar) is applied. Often found in areas that were once prehistoric seabeds.