sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3 (Mohs scale), Color: tan-yellowish, Luster: dull to earthy, Crystal Structure: Trigonal (often microscopic), Cleavage: Rhombohedral (not visible in grain), Specific Gravity: 2.5-2.7

Identified July 15, 2026More sedimentary →

Explore Limestone in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 3 (Mohs scale), Color: tan-yellowish, Luster: dull to earthy, Crystal Structure: Trigonal (often microscopic), Cleavage: Rhombohedral (not visible in grain), Specific Gravity: 2.5-2.7

Formation & geological history

Formed in marine environments through the accumulation of shell, coral, and algal debris over millions of years. This specimen appears to be a clastic sedimentary rock composed of lithified carbonate sediment.

Uses & applications

Used widely in construction (aggregate), cement manufacturing, agriculture (as lime), and as a building stone. Also used in the steel and chemical industries.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is highly susceptible to acid rain and carbonation, which leads to the formation of caves and karst landscapes.

Field identification & locations

Identify in the field by testing with a drop of cold 10% hydrochloric acid; it will effervesce (fizz) vigorously. It feels gritty if it contains sand but generally has a softer feel than quartz-based rocks.