Limestone is a sedimentary rock, specifically a carbonate sedimentary rock made mostly of calcium carbonate.

Rock type

  • Limestone is classified as a sedimentary rock formed at or near Earth’s surface from accumulated material.
  • More precisely, it is a carbonate rock composed mainly of calcite or aragonite, both forms of calcium carbonate.

How it forms

  • Many limestones are biological, forming from shells, corals, algae, and other skeletal debris that pile up on sea floors and get compacted into rock.
  • Limestone can also form chemically when calcium carbonate precipitates directly from water in marine or lake environments.

Quick extra facts

  • Limestone often contains visible fossils, which makes it important for studying past environments and life.
  • It is common in warm, shallow marine settings and is widely used as building stone and as raw material for cement and lime.