You're probably very familiar with beach sand. Perhaps you've left your footprints in it. You may have built castles with it. Maybe you've gotten it in your shoes or in your sandwich. But did you ever wonder what it was?
Silica sand is the most common type of beach sand. It consists primarily of grains of quartz, although varying amounts of other minerals can be part of the mix. Silica sand is created through the processes of mechanical and chemical erosion that liberate quartz and other grains from the rocks in which they were originally incorporated. Streams and rivers carry the particles to the ocean, and on the way the grains become worn and rounded. High concentrations of quartz tend to produce beach sand that is lightly colored.
White beaches feature another type of sand, calcareous sand. Calcareous sand is comprised primarily of grains of calcium carbonate. Common sources include shells and skeletons of mollusks and echinoderms, staghorn coral, flakes of green algae, and single-celled animals called foraminifera. Bioerosion plays an important role in the creation of white sand. And, yes, so do parrotfish. Parrotfish eat algae by nibbling it off coral reefs. In the process they also ingest coral. The coral passes through their digestive track and is excreted as white sand. According to Siim Sepp, creator of Sandatlas.org, "One parrotfish can make 90 kg [nearly 200 pounds] of coral sand a year."
Some beaches have black or green sand. Black sand is formed from mafic rocks, that is, those that contain higher concentrations of iron and magnesium. The rarest form of beach sand is green. Its grains are formed when olivine crystals are eroded out of basalt (an ultramafic rock) from lava flows.
Sand dunes are created through a repeating cycle by which the wind deposits sand in a mound. When the accumulation becomes sufficiently steep, the sand pile collapses. Eventually, the sand mound grows with a gentle wind-facing slope and a steeper side opposite the slope called the slip face. Stable dunes serve to protect land areas behind them, but sand dunes are typically fragile. Plants help bring stability to these fragile structures.
This article, along with more images and links to resources, originally appeared in the June 2016 issue of Observations: A Pier Press® Newsletter. To view the complete newsletter, visit our online archives. Also, please consider becoming a subscriber so that future editions can be delivered directly to your inbox. Subscriptions are free!