When it comes to white, powdery sand, nothing compares with Siesta Key, Florida. In fact, at the Great International Sand Challenge, held in 1987, the sand at Siesta Key’s Crescent Beach was rated “The World’s Finest, Whitest Sand,” beating out more than 30 other entrants, including those from the Bahamas and Grand Cayman. The competition was judged by Dr. David Aubrey, a beach expert and the Director of the Woods Hole Oceanographic Institution’s Coastal Research Center.
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It’s clean, it’s dazzling white and it feels like confectioner’s sugar.
Why? It’s the quartz. A study of Siesta Key beach sand by Harvard University’s geology department found that the sand consists of 99 percent pure quartz grains, ultimately derived from the southern Appalachian Mountains. Over millennia, sand grains were carried by rivers into the Gulf and south along Florida’s coast. Those quartz grains are very fine, without any coral or shell fragments, which results in sand with a soft, flour-like texture.
Quartz sand comes from igneous rock, the kind of rock that once was molten. Quartz is a very hard substance, graded as seven on a hardness scale of one to ten. Diamonds are rated as ten on this scale. Minerals with a hardness grade of seven cannot be scratched with the point of a steel knife. The most common such substance is granite.
The fine sand has passed through one or more of what geologists refer to as “eolian cycles.” Those are periods when the sand grains were blown about by the wind. Such cycles tend to smoothen the sharp corners of the quartz grains and result in the somewhat angular grain structure of Crescent Beach sand.
