Limestone is formed predominantly from calcium carbonate.
Limestone is made up mainly of the mineral calcite (or calcium carbonate), usually mixed with small amounts of other minerals such as sand, magnesium carbonate and clay. It is a sedimentary rock, which means that it was formed by water or wind deposits.
The calcite in limestone is usually formed by accumulated shells and remains from hard organisms such as mollusks, corals and brachiopods. For this reason, beds of limestone can often been found on the site of ancient reefs. Limestone can also be formed from calcium deposits in seawater.
Geology and Paleontology
Because limestone is often formed from crystallized bio-matter and seawater deposits, it is important in the fields of geology and paleontology. Geologists often study beds of limestone because they indicate the location of ancient reefs and seas, while the way it is formed makes it an excellent place for paleontologists to find fossils.
Limestone has many uses in the construction industry. It is heated along with powdered clay, sand and ground rock in a rotating kiln to make cement. Glass is made of sodium carbonate, sand and limestone. Limestone is also used as a building material for facades and as ballast in road construction.