All About Sand

Probably most of us haven't given much thought to sand, which is as just about everyone knows, simply a large collection of tiny rocks. Like other types of soil, it comes from the breakup in ages gone by of the solid rocky surface of the earth. But the rock fragments that formed sand were those too hard or too resistant to chemical action to be broken up or dissolved into a fine powdery mass like other soils. Instead they remained in gritty particles from a tenth to a hundredth of an inch in diameter.

How did these grains of sand become separated from the finer, softer soils, so that we find them in huge deposits in the beds of streams and along the shores of the ocean? We can find the answer if we put a mixture of gravel, sand, and fine sand in a can or box and shake it from side to side for a few minutes. The coarse gravel will come to the top, the sand will be next, and the fine powder soil will make its way to the bottom of the container.

This is always the result when objects of about the same weight, but of different sizes are shaken up together. The smaller ones shift through the open spaces that are left between the larger ones and so gradually work down under them and force them to the top.

So, when gravel and sand were formed in the breakup of ancient rocks, they tended to always remain on the surface. There floods and torrents could get at them and roll them down to the valleys and river beds. As they rolled, many gravel pebbles were cracked and worn down into sand grains.

We can tell something of the history of sand grains by examining them with a magnifying glass. Smooth well-rounded particles either have traveled far or have been continuously churned around like those on surf-beaten shores of the ocean.

Those with sharper edges have splintered off more recently and not strayed very far from where they originated. As a rule, each grain is composed of only one mineral, but there may be a variety of mineral species in one handful of sand.

The most common is quartz sand. Pure white and silvery sands are not uncommon, but shades of yellow, brown, and red predominate, owing to the presence of iron compounds.

Magnetite sand is black or gray and glauconite sand is green. There are also sands that contain gold, zircon, garnet, pyrites, and other rarer minerals.

The so-called "white sands" of New Mexico are nearly pure gypsum.

Arkose sand contains feldspar, hornblende, mica, etc. Sands made of fine grains of olivine are found along the Bay of Naples.

It is important to know that sand of wholly different origin is shell sand. It consists of fragments of shells and coral ground up by the waves. Great deposits of shell sand lie on the coasts of Devonshire and Cornwall in England, in Bermuda, and on the shores of many Pacific Islands.

Dry sand is blown about extensively by the wind. Any obstacles on the surface, such as rocks, stumps, or shrubs, will stop some of it, forming little mounds. These block more sand until they grow into high ridges and hills called dunes. These mounds, or dunes, are common along sandy shores. They abound also in many deserts and in semi-arid regions, such as western Nebraska.

Unless anchored by vegetation, dunes are likely to migrate by the slow shifting of the sand from windward to the leeward side of the dune. Migrating dunes have invaded many a fertile farm and fruitful orchard.

It is a matter of recorded history that near Manistee, Michigan, a bonfire built by picnickers on a stationary dune burned off the grass which held it in place. The wind biting into the bare patch undermined the live grass left around the edges and soon stripped one side bare. Then, the great hill of sand began to roll forward, and before it was pinned down by replanting it, it almost buried the city waterworks and property.

In New Zealand, sheep pastured on grass-covered dunes have done similar damage. Another example, was the great estate of Culbin, on the northern coast of Scotland, celebrated for its fertility, that was engulfed in sand toward the end of the 17th century, and ever since, the entire region (about 3,000 acres), that was left to be nothing but a shifting waste. Additionally, large cities lie buried under the sand hills of the Gobi Desert in Central Asia.

Sand mixed with water behaves very differently from dry sand. Walking along the dry part of a sandy beach our feet sink deep. But when we step over to the wet strip along the shore we find a frim and solid footing. On the Florida coast at Dayton Beach, the damp, hard-packed sand beach was in the past even used for automobile racing.

Firmness is characteristic of sand wet with just enough water to fill the spaces between the grains. Quicksand, on the contrary , is sand so saturated and churned up in water that it will support no weight.

In ages gone by, sediment from ancient oceans and lakes deposited itself on sandy bottoms. The sediment contained lime, chalk, and silica from the shells and bodies of billions of water creatures. It penetrated between the sand grains and later, under heavy pressure of the overlying deposits, it cemented them together into sandstone. Thus, the tiny fragments of primitive rocks were turned into solid rock again.

Still later, vast layers of this sandstone were thrust up into dry land by movements in the earth's crust and are found today in many parts of the earth.

Certain varieties of sandstone are used for building, others for grindstones. Quartzite is a rock in which the silica cement has crystallized around grains of quartz sand.

We once stayed in a motel in Belize, called the Singing Sands. Until that first night, neither of us knew that there is such a thing as "singing sands." So-called "musical, singing, or barking sands occur in various parts of the world. Sand on the beach near Manchester, Massachusetts, gives a crackling sound when walked upon.

The "singing sands" of Mount Sinai are sad to give a harp-like note when masses of it are tumbled down hill.

Under the same conditions sands on the Hawaiian island of Kauai produce a deep note, but when stirred up with the hands they emit a "barking sound."

In many places windblown sands remind people of a humming electrical wire. The cause of these sounds has been much discussed by the scientific community. One explanation is that the grains of the sand in question are all of the same size and shape. When slightly damp so that an elastic film of moisture surrounds each grain, the sand is easily set into uniform vibration.

Sand is an important ingredient of mortar, of concrete, and of asphalt pavings, and is used for molds in metal foundries. Bricks made of clay mixed with sand are harder and will bear a greater weight than bricks of clay alone.

• Sand is used as a filter to purify water.
• Sand is an excellent abrasive.
• Glued to paper it becomes sandpaper.
• Blown through a hose by compressed air or steam,t and corrosion from metals, for it gives us the sandblast, which is used to clean the fronts of brick or stone buildings, to scour rust.
• Sand is used for engraving glass.
• Sand is used for cutting inscriptions on monuments.