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The examples and perspective in this section may not represent a worldwide view of the subject. Because of its extremely small grain size, oolitic sand has a lot of surface area, which promotes high bacterial growth. This unusually smooth sand promotes the growth of bacteria, which are important biofilters in home aquaria.

Also known as 'oolitic' sand, the sugar-sized round grains of this sand pass easily through the gills of gobies and other sand-sifting organisms. Oolites are often used in the home aquarium industry because their small grain size (0.2 to 1.22 mm) is ideal for shallow static beds and bottom covering of up to 1' in depth. The size of the oolites reflect the time that they were exposed to the water before they were covered with later sediment. The oolites are commonly found in large current bedding structures that resemble sand dunes. Strong intertidal currents wash the 'seeds' around on the seabed, where they accumulate layers of chemically precipitated calcite from the supersaturated water. The mechanism of formation starts with a small fragment of sediment acting as a 'seed', such as a piece of a shell. They are usually formed in warm, supersaturated, shallow, highly agitated marine water intertidal environments, though some are formed in inland lakes. Oolitic hematite occurs at Red Mountain near Birmingham, Alabama, along with oolitic limestone. Dolomitic and chert ooids are most likely the result of the replacement of the original texture in limestone.

Ooids are most commonly composed of calcium carbonate ( calcite or aragonite), but can be composed of phosphate, clays, chert, dolomite or iron minerals, including hematite. The term oolith can refer to oolite or individual ooids. Strictly, oolites consist of ooids of diameter 0.25–2 millimetres rocks composed of ooids larger than 2 mm are called pisolites. Oolite or oölite (from Ancient Greek ᾠόν (ōión) 'egg stone') is a sedimentary rock formed from ooids, spherical grains composed of concentric layers. Thin-section of calcitic ooids from an oolite within the Carmel Formation (Middle Jurassic) of southern Utah

Oolite stone