But Indiana's most famous and important souvenir of ancient seas is Indiana limestone. Adopted as the state rock in 1971, it might be thought of as Indiana's official fossil. A souvenir of ancient seas, limestone is made of the remains of countless marine animals, but mostly from the shells of tiny animals. It is made of a mineral called calcium that is used to make bones and shells. Fossils of larger animals that sank to the seafloor after they died are also found in limestone.
Limestone covers vast areas of the Midwest and is of great commercial importance.
Indiana is home to some of the most famous limestone in the world. It is known for its strength, attractive color, durability, and abundance. Coral reefs dotted warm, shallow seas covering northern and central Indiana. Over millions of years, sediments buried the reefs, which became part of limestone. The chief deposits are in south central Indiana, though extensive layers underlie much of the southern part of state.