Sand is composed of particles of minerals, rock, or soil, with quartz being the most common constituent. Peaks that once stood rock solid have eroded into sand. How does such erosion occur?
Sand is often the product of ocean violence. Waves smash against coastal cliffs, and these collisions loosen and rip away slabs of rock. Very large pieces surrender before the unremitting assault, being sloughed off in chunks into the surf. The churning sea grinds off sharp edges, producing boulders. Constant motion gradually wears them into pebbles, and these are crushed into still smaller particles, which we know as sand. Sometimes the sea carries the sand off, but in many places, waves heave the sand back ashore, leaving pristine beaches.
When cold weather combines with ocean violence, frozen water becomes trapped in rock, producing icy wedges that split the stones. The fracturing goes on, reducing large rock masses to smaller and smaller pieces, which eventually become sand.
The wind too plays a role, lifting grains of sand and driving them against rock masses. The abrasion creates more sand. Layers of rock hundreds of feet thick give way before this natural form of sandblasting. Meanwhile, the wind scatters the resulting sand, stretching it out like a carpet on the desert floor.
Over millenniums, these harsh processes have yielded countless tons of sand. Many people would be delighted if it were used only to provide contoured cushions at the beach. But sand’s value reaches far beyond the shore, as we shall see.
Tiny Grains, Huge Benefits
To a large degree, our eating and drinking is dependent on sand. How is that? In one way or another, all our food comes from the vegetation of the earth. Sand and its finely ground cousins silt and clay supply minerals that plants need. Also, sand in the soil allows air and water to circulate. Thus, plant roots can easily absorb nutrients. But how is sand involved in quenching our thirst?
If you fill a one-quart [one-liter] jar with dry sand, you can add a third of a quart [300 milliliters] of water to that same jar without making it overflow. This is so because sand is porous
Geological formations called aquifers lie below much of the earth’s surface. Composed of vast layers of sand and other porous minerals, these contain water that has been filtering downward for possibly thousands of years. Scientists calculate that these unseen “water jars” hold 40 times more fresh water than all the lakes and rivers on earth. Wells tap aquifers for their precious liquid, which sustains the lives of millions.
Sand Before Your Eyes
You may be walking on sand every day without ever going to the beach. Are streets or sidewalks in your hometown paved with concrete? In some cases, sand makes up one quarter of this common building material. Hundreds of millions of tons of sand are consumed annually as construction material, so much so that some places have experienced shortages of sand.
While sand generally lies underfoot, in another form it may be right before your eyes. The screen on your computer is likely made from sand, as are the lenses of mountaintop telescopes and desktop microscopes. The same is true of crystal vases and your bathroom mirror. Those items are all made of glass, and sand constitutes over half the raw material that is used in glassmaking. How is sand used to make glass?
Sand and other ingredients are mixed and then melted at temperatures exceeding 2,600 degrees Fahrenheit [1,400°C]. The resulting viscous liquid can be rolled, blown, bent, drawn, and spun into almost any form. Glass fibers are even woven into cloth. But whether it promotes beauty or industry, whether it refracts or reflects, smooth, clear glass comes from the opaque grit of sand.
Sand on the Move
Imagine a hill 250 feet [75 m] high that moves. This happens when piles of sand called dunes migrate, pushed by the wind. In some parts of the Sahara, dunes seem to string out their undulating ridges endlessly.
When humans establish themselves nearby, dunes may pay them an unpleasant visit. Indeed, sand on the move has been known to block highways, swallow houses, and bury entire towns.
Abounding With Life
As lifeless as sand may appear, many creatures call it home. Foxes, snakes, and scorpions burrow in desert sand during the day. Sleeping through the heat, they come out at night to hunt for food. Along Namibia’s Skeleton Coast, in southwest Africa, elephants roam the vast dunes. They seem to have fun on the steep, sandy inclines, sliding down dragging their back legs. The “ship of the desert,” also known as the camel, cruises the sand seas of Asia and Africa.
Some animals come up out of the ocean to make use of sand. When their biological clocks sound the alarm, horseshoe crabs, sea turtles, and small fish called grunions ride the surf to the shore. There they lay their eggs to incubate in the softness of the sand.
For certain flowers, a dune is as comfortable as a window box. Sea rockets, beach peas, and beach morning glories flourish in sand and push their heads back up even when a dune buries them. Their long roots pull up water and nutrients to feed dainty blossoms
Sand comes in a variety of colors. In different lands, you can find sands that are pitch-black, snow-white, purple, gray, red, orange, yellow, and many hues in between. Some include a mixture of crushed seashells. The array of color and texture in sand fascinates some people to the point that they have taken up collecting sand. Many find themselves trading sand, traveling to find it, and stooping to gather samples of it in small glass bottles, new additions to their collections. They call themselves arenophiles, meaning “lovers of sand.”