Oolitic aragonite sand is composed of the calcium carbonate mineral,

aragonite Aragonite is a carbonate mineral, one of the three most common naturally occurring crystal forms of calcium carbonate, (the other forms being the minerals calcite and vaterite). It is formed by biological and physical processes, including pre ...

, with an egg-like shape (" oolitic" from the Ancient Greek word ᾠόν for "egg") and

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class o ...

grain size. This sand type forms in tropical waters through

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...

sedimentation Sedimentation is the deposition of sediments. It takes place when particles in suspension settle out of the fluid in which they are entrained and come to rest against a barrier. This is due to their motion through the fluid in response to the ...

, and microbial activity, and is indicative of high energy environments. The production of oolitic aragonite sand in the

Bahamas The Bahamas (), officially the Commonwealth of The Bahamas, is an island country within the Lucayan Archipelago of the West Indies in the North Atlantic. It takes up 97% of the Lucayan Archipelago's land area and is home to 88% of the ar ...

surpasses anyplace else in the world. Changes in seawater chemistry and paleoenvironments can be interpreted by the sand's chemical composition and structure.

Formation

Oolitic aragonite sand forms in high-salinity waters that are turbulent, shallow, and warm. The sand starts to form around a nucleus of calcium carbonate, such as a

peloid Peloid is mud, or clay used therapeutically, as part of balneotherapy, or therapeutic bathing. Peloids consist of humus and minerals formed over many years by geological and biological, chemical and physical processes. Numerous peloids are av ...

, shell fragment, or

foraminifer Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly an ...

. The nucleus is coated with a thin layer of crystalline carbonate to form the cortex of the ooid. Compared to other types of sand formation that involve the weathering and erosion of a larger rock by turbulent waters, oolitic aragonite sand is created by dissolved calcium carbonate joining with the cortex or nucleus of the

ooid Ooids are small (commonly ≤2 mm in diameter), spheroidal, "coated" (layered) sedimentary grains, usually composed of calcium carbonate, but sometimes made up of iron- or phosphate-based minerals. Ooids usually form on the sea floor, mo ...

. The dissolved calcium carbonate in seawater continues to stick to the cortex and is combined with the high velocity water which creates the smooth, granular shape resulting in the aragonite composed ooid.

Biomineralization Biomineralization, also written biomineralisation, is the process by which living organisms produce minerals, often to harden or stiffen existing tissues. Such tissues are called mineralized tissues. It is an extremely widespread phenomenon; ...

involving microbial organic matter likely also plays an important role in

formation.

Localities

Bahamas

Because of the waters of the

are warm with shoals that create rough waters, the conditions for oolitic aragonite sand are optimal and results in the high rate of formation and accumulation. The Great Bahama Banks has been accumulating oolitic sand in the late

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

period and contains the largest reservoir of oolitic aragonite sand in the world.

Great Salt Lake, Utah

Oolitic sand beaches form on the banks of the Great Salt Lake in Utah, USA including the shorelines of its islands.

Paleoproxy

Scientists use oolitic aragonite sand to reconstruct the route and speed of past currents and ocean circulation patterns. The grain size and sand body size indicate the strength of the current that formed the oolitic sand. The level of turbulence that causes ooids to form such concentric shapes is indicative of intensity of the current. The more circular the ooids, the higher the turbulence, and thus, the more intense the current must have been during ooid formation. The location of ooid accumulation indicates the direction of the current.

Commercial uses

Commercial uses are similar to

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

and other high calcium carbonate materials. One popular use is in reef aquariums.{{cite web, url=http://www.saltcorner.com/Articles/Showarticle.php?articleID=114, title=Marine Aquarium Substrates – Materials & Methods

References

Sediments