In geology, ooids are small (< 2mm) calcium carbonate or iron coated grains that usually form on the sea floor. After being buried under additional sediment, these grains can form into a sedimentary rock, called an oolite. Oolites usually consist of calcium carbonate meaning they belong to the limestone rock family. Ooids usually form in shallow tropical regions, for example the Bahaman Platform. Pisolites are ooids that are greater than 2mm in diameter. Geology (from Greek γη- (ge-, the earth) and λογος (logos, word, reason)) is the science and study of the Earth, its composition, structure, physical properties, history and the processes that shape it. ... An Oolite (or an oolith or ooid) is a sphere typically consisting of several concentric layers of calcite or aragonite (forms of calcium carbonate) that was created by precipitation in the supersaturated warm waters of shallow tropical seas. ... Limey shale overlaid by limestone. ...

An ooid forms by a series of concentric layers around a nucleus. The layers contain crystals arranged radially, tangentially or randomly. The nucleus can be a shell fragment, quartz grain or any other small fragment (including an aragonite/calcite amalgamation). Modern ooids are exclusively aragonite (a neomorph of calcite). Ancient ooids are calcite, which is either a replacement of aragonite or directly precipitated.

Similar to a snowball, which accumlates more snow as it rolls down a hill, ooids form by growing larger and accreting material as they move around. There are several factors that affect ooid growth: su[ersaturaiton of the water with respect to calcium carbonate, the availability of nuclei, agitation of the ooids, a constant location, water depth and the role of microbial organisms.

Kidney stones are a type of ooid, as they are rich in calcium and possess similar growth structures. Kidney stones, also known as nephrolithiases, urolithiases or renal calculi, are solid accretions (crystals) of dissolved minerals in urine found inside the kidneys or ureters. ...

External link

• Sculpture Conservation: Ooids and Ooites
• Ooid Formation