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White Sand

The Grand Bahama Banks, where ooliths are forming today

Q: Recently I was on vacation in Jamaica and I became curious about one issue. Almost all Jamaica shore is hardly eroded except the west coast of the Island, which has some magnificent white sands beaches at Negril. Why is this sand so white?

From Mr Antonio Almeida (October 2009)

Reply by Dr Ted Nield

Thank you for your question. White sand - really truly brilliantly white sand – has only one explanation. It is calcium carbonate, and there are two main ways for it to form beaches. First, it is secreted by corals and other sea creatures and these contribute their material to the sediment when they die.

These fragments can sometimes also form the nucleus for chemical precipitation of calcium carbonate directly from seawater. In some environments close to the surface, the rolling action of the waves can cause these objects to become very smooth and round – perhaps a millimetre or two in diameter. These, because of their resemblance to fish eggs, are called “ooliths”. They can also end up on beaches inshore from the usual offshore sand-bank environments where they tend to form.

Because of the productivity of carbonate environments, the sand locally is independent of the type of bedrock, which contributes typically next to nothing in terms of eroded material to the local sediments.