Features of Limestone

Composition

• The term "limestone" refers to any rock that contains at least 50 percent calcium carbonate in the form of calcite. This calcite often comes from the remains of shelled sea animals like clams and corals. Limestone can take on a wide variety of appearances because it can contain many other substances in addition to calcite, including pyrite, quartz and sand particles.

Formation

• Limestone is a sedimentary rock, which means that it is formed by the accumulation and consolidation of loose materials called sediments. On the ocean floor, the shells of sea animals can accumulate after they die and can become limestone over time. Limestone can also form through evaporation: underground, calcium-containing water can seep through the earth into caves. When this water evaporates, the calcite remains. This evaporation process explains the strong presence of limestone in many underground caves.

Types

• There are seven different types of limestone. Chalk is a kind of limestone that is soft and white or gray and is formed from the remains of marine organisms. Coquina is a brittle limestone that often collects on beaches. Fossiliferous limestone contains many conspicuous fossils. Lithographic limestone is dark and smooth-surfaced and was a major part of lithography in the 1700s. Travertine is limestone formed by evaporation, usually in caves. Precipitation at calcium-rich sites like certain hot springs or lakes forms the limestone tufa. Oolitic limestone contains small spherical markings called "oolites."

Uses

• Limestone has a wide variety of applications. Because of its high calcium content, it has been used sparingly in the feed of chickens to produce stronger eggshells and in the feed of some dairy cattle to replenish calcium lost through milking. Limestone is an important source of calcium oxide, or lime, which is used as a soil treatment agent in farming throughout the world. Limestone is also a crucial element of cement.