Oolite

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An oölite (egg stone) is a sedimentary rock formed from oöids, spherical grains composed of concentric layers. The name derives from the Hellenic word òoion for egg. Strictly, oölites consist of oöids of diameter 0.25–2 mm: rocks composed of oöids larger than 2 mm are called pisolites.

Composition

Oöids are most commonly composed of calcium carbonate (calcite or aragonite), but can be composed of phosphate, chert, dolomite or iron minerals, including hematite. Dolomitic and chert oöids are most likely the result of the replacement of the original texture in limestone. Oolitic hematite occurs at Red Mountain near Birmingham, Alabama along with oolitic limestone.

Occurrence

Some exemplar oölitic limestone, a common term for an oölite, was formed in England during the Jurassic period, and forms the Cotswold Hills, the Isle of Portland, and part of the North Yorkshire Moors. A particular type, Bath Stone, gives the buildings of the World Heritage City of Bath, their distinctive appearance.

This type of limestone is also found in Indiana in the United States. The town of Oolitic, Indiana was founded for the trade of limestone and bears its name. Quarries in Bedford, Oolitic, and Bloomington contributed the materials for such iconic US landmarks as the Empire State Building and the Pentagon. The Soldiers' and Sailors' Monument in downtown Indianapolis is built almost solely of grey oölitic limestone.

The movie Breaking Away centers around the sons of quarry workers in Bloomington, the home of Indiana University. Almost all of the buildings on the Indiana University campus are built with native oolitic limestone material.

Roggenstein is a term describing a specific type of oolite one in which the cementing matter is argillaceous.

Oolite

Composition

Occurrence

See also