Most of the sand you have encountered at beaches is from the weathering, breaking down, or erosion of organic sources, like rocks or shells. Some of this sand can be really fine from years and years of this process, but did you know in certain warm water environments, like the Great Bahama bank, the sand grows?

The word ooid is taken from the Greek word egg. Ooids look like very tiny fish eggs and have an odd formation, on that has taken the interest of a lot of geologist, chemist, and geo-biologist. Ooids are formed when a nucleus of various material, also known as the seed, gets coated by very thin layers of crystalline calcium carbonate to then form the ooid. They normal grow to around 0.25mm to 2mm in size. Once above 2mm, they are considered a pisoids. Not only is it warm climate settings important for their growth, but also shallow water and strong waves. The waves help roll around and agitate the Ooids to help facilitate growth and also smoothing out each layer. The water also should be rich with calcium carbonate to actually form each layer. With these three things, a nice spherical grain can form over a hundred or so years.

Because of Ooids specific growing conditions, they can give us information on past ocean basins. These little sand grains can be found fossilized in places not just within oceans. This tells researchers that these areas might have had warmer, more agitating, and supersaturated waters many years ago. And since seawater chemistry is very intertwined with the carbon cycle, we can also get good look at our Earths climate history. Along with the ability to look at past water chemistry through ooids, we can also them now as an active recorder of what is going on in the seawater.

I personally find the whole concept of ooids quite fascinating. I first learned about them at the Cape Eleuthera institute in the Bahamas. We went out to a little sand bar and learned all about them. They told us it was “the perfect exfoliant”. The fact that this grain builds up and not breaks down is truly one of a kind to me.