Limestone is a prevalent carbonate sedimentary rock that serves as the primary source of lime. Its composition is dominated by calcite and aragonite, which are distinct crystalline forms of calcium carbonate. This rock is formed through the precipitation of these minerals from water, a process that can occur via both biological and nonbiological pathways.
Over the last 540 million years, biological activity—such as the accumulation of marine shells and coral—has played a major role in limestone formation. Because of its sedimentary nature, limestone frequently contains fossils, which serve as valuable records for scientists studying ancient environments and the history of life on Earth.