sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 on Mohs scale; Color: typically gray, white, or tan; Luster: dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific gravity: 2.71.

Hardness: 3 on Mohs scale
Color: typically gray, white, or tan
Luster: dull to earthy

Identified February 18, 2026More sedimentary →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 3 on Mohs scale; Color: typically gray, white, or tan; Luster: dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Perfect rhombohedral; Specific gravity: 2.71.

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 ocean or lake water. Most deposits range from the Paleozoic to Mesozoic eras.

Uses & applications

Used extensively in construction as road base, railroad ballast, and an ingredient in cement. In industry, it is used for steel manufacturing, glass making, and as a soil conditioner in agriculture.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. Famous structures like the Great Pyramid of Giza and the Parthenon were constructed using various forms of limestone.

Field identification & locations

Identify in the field by its reaction to dilute hydrochloric acid (it will fizz/effervesce). It often contains visible fossils. Commonly found in areas that were once covered by ancient seas, such as the Midwestern United States and Western Europe.