sedimentary

Limestone

Calcium Carbonate (CaCO3)

Hardness: 3-4 on Mohs scale; Color: Cream, tan, or light gray; Luster: Dull to earthy; Crystal structure: Trigonal (as calcite); Cleavage: Rhombohedral (in crystal form) but usually massive; Specific gravity: 2.5-2.7

Hardness: 3-4 on Mohs scale
Color: Cream, tan, or light gray
Luster: Dull to earthy

Identified May 16, 2026More sedimentary →

Identify your own rocks.

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

App Store Google Play

Physical properties

Formation & geological history

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

Uses & applications

Extensively used in construction as building stone, road base, and as a primary ingredient in cement and lime. Also used as a soil conditioner in agriculture and as a filler in toothpaste and paints.

Geological facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary rock type found in karst landscapes, leading to the formation of most of the world's caves.

Field identification & locations

The easiest field test is the acid test; it will effervesce (fizz) when a drop of dilute hydrochloric acid or vinegar is applied. Often contains visible fossils of ancient marine organisms. Found worldwide in ancient seabed deposits.