Silicon – usually, as quartz crystals – is the primary component of most of the world’s light-coloured ocean beaches.
However, in tropical and subtropical waters where coral reefs thrive, calcium carbonate is more likely to be a so-called “white” sand beach’s “hero” ingredient.
Grains of coral sand consist mainly of calcium carbonate — the mineral that makes the skeletons and shells of corals, clams, and other marine organisms large and small. When the organisms die, these structures are broken apart and ground to bits by the force of waves and water currents, and by other creatures. In fact, if you look at coral sand under a microscope, you can see some of the colors and textures of the original shells.
Some of the sand comes from living organisms — especially corals. Algae, worms, sponges, and others can bore into living coral, chipping off some of the coral’s external skeletons. And fish can break off little chunks when they graze on coral animals and algae.
To extract the tender animals from their stony skeletons, for example, a parrotfish uses specially adapted teeth in its throat to grind the chunks of coral to the consistency of sand. The fish swallows the animals with the sand, then excretes the sand into the water with the rest of its wastes.
The italicised text was written by Damond Benningfield for the University of Texas’ “Science and the Sea”.
The pictured example is a beach on Batanta, which is the smallest of the four largest islands in eastern Indonesia’s Raja Ampat.
”Raja Ampat” translates as “the four kings”; Raja Ampat in fact includes another 1,500+ islands and islets, surrounded by what are almost certainly the most species-diverse reefs on “our” planet.
Our October 2024 visit to Marandan Weser village was unforgettable; eventually, this will be explained and illustrated in a separate series of posts.
This “Grand sands” series has just one more chapter.
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