So Is All This Sand Just A Bunch Of Tan Rocks?

No! The sand you’re stepping on has a deep, dark, and tortuous past
BY: ANNE TEAK

Sand blankets the beaches, riverbeds and deserts of the world. Composed of different materials that vary depending on location, sand comes in an array of colors including white, black, green and even pink.

The most common component of sand is silicon dioxide in the form of quartz. The Earth’s landmasses are made up of rocks and minerals, including quartz, feldspar and mica. Weathering processes — such as wind, rain and freezing/thawing cycles — break down these rocks and minerals into smaller grains.

Unlike some other minerals, quartz is hard, insoluble in water, and doesn’t decompose easily from the weathering processes. Streams, rivers and wind transport quartz particles to the seashore, where the quartz accumulates as light-colored beach sand.

Tropical islands, such as the Hawaiian Islands, don’t have a rich source of quartz, so the sand is different there. The beach sand on tropical islands often looks white because it is made up of calcium carbonate, which comes from the shells and skeletons of reef-living marine organisms, including corals, mollusks and little bitty organisms.

Sand forms when the reef breaks down, either by mechanical forces — such as waves and currents — or from bio-erosion caused by grazing fish, urchins and other marine life. The famous pink sand of Bermuda is also composed of eroded calcium carbonate; the sand gets its ruddy hue from the abundant red foraminifera.

Tropical beaches may also have black sand, which is composed of black volcanic glass. Sometimes, erosive forces separate the mineral olivine from other volcanic fragments, leading to green sand beaches, such as Hawaii’s Papakolea Beach.

Surprisingly little is known about the origin of all that sand in the world’s largest deserts, but research suggests that the Sahara Desert was once lush with vegetation before a change in climate turned it into a desert, part of which is covered in sand. On the other hand, the sand in the Namib Desert in southern Africa may have been blown in by wind from the Orange River in South Africa.

Beaches are temporary features. With beaches, there is always sand coming and going. Often, the beaches change drastically throughout the year, depending upon the frequency of storms.

Sand can also be transported from beach to beach along a shoreline but this is mostly just a redistribution of sand that is already on the coast.

When the ever moving and sometimes encroaching sea comes against people’s property, the tendency is for people to try and stop it. They armor the shoreline with seawalls, revetments, and jetties and such, but these actually have a negative effect on beaches because once sea water reaches them, it “bounces” off them with more energy than a wave washing back off a normal sand beach. So now more sand is carried off shore, promoting more beach loss. Jetties placed perpendicular to the beach aren’t always a good solution, either, because they disrupt beach currents and cause sand loss downstream of the jetty.