Limestone

A stratigraphic section of Ordovician limestone exposed in central Kentucky, USA. The less-resistant and thinner beds are composed of shale A stratigraphic section of Ordovician limestone exposed in central Kentucky, USA. The less-resistant and thinner beds are composed of shale
Thin-section view of a Middle Jurassic limestone in southern Utah.  The round grains are ooids; the largest is 1.2 mm in diameter.  This limestone is an oosparite. Thin-section view of a Middle Jurassic limestone in southern Utah. The round grains are ooids; the largest is 1.2 mm in diameter.
Limestone is the most abundant of the non-clastic sedimentary rocks. Limestone is produced from the mineral calcite (calcium carbonate) and sediment. The main source of limestone is the limy ooze formed in the ocean. The calcium carbonate can be precipitated from ocean water or it can be formed from sea creatures that secrete lime such as algae and coral.