Rae Ann Smith, age 13, of Columbus, Ohio, for her question:
WHAT IS SAND?
Sand is any earth material that consists of loose grains of minerals or rocks larger than silt but smaller than gravel. Geologists measure sand by shaking it through wire screens. Sand includes all grains that are less than one twelfth of an inch but greater than one four thousandths of an inch in diameter.
Geologists find many types of minerals in sand. The most common is quartz. Some sand consists almost entirely of quartz, but usually grains of other minerals are also present.
Other sand, such as that found on the beaches of many Pacific islands, consists of grains of basalt. Basalt is a black lava rock that has flowed from or has been blown out of volcanoes on these islands.
Some Pacific island beaches have sand that is made of tiny particles of coral and shells of clams and snails which have been broken up by the waves.
Some river sands are rich in precious metals. These mineral deposits are called "placers." The California pioneers took many millions of dollars worth of gold from placers. Platinum, diamonds and other valuable minerals also come from placers. Rare metals for jet engines come from placers that are found in Florida, India and Australia.
Most grains of sand are parts of solid rock that have been crumbled away. Rocks break down in many ways. Some rocks crumble by the action of the air, rain or frost. Strong waves wear away rocks by rolling over and breaking against them.
Sand is widely distributed on the surface of the earth. It is also found at the bottom of the seas and in shallow lakes. Sand is also rolled along the bottom of rivers and may be spread by the rivers over lowland areas. Great quantities are found on beaches.
In desert areas, sand covers vast stretches of land. Often sand is piled up by desert winds into hills that are called "dunes." These dunes have buried some ancient towns for hundreds of years.
Sand has many practical uses. Manufacturers use quartz sand to make chemicals and glass. They make sandpaper by gluing loose sand onto heavy paper. Sand is also used in mortar and concrete.
Sandstone is rock that is made up of grains of sand. The sand grains are actually cemented together by some substance, usually silica, clay or carbonate of lime.
Some sandstone contains quartz and looks glassy. This variety is used in making glass. Sandstone ranges in color from white to dark gray or brown. The cement gives sandstone its color.
Brownstone, a reddish brown variety of sandstone, was once widely used in building houses in the eastern part of the United States. Before the use of Portland cement and reinforced concrete, sandstone was widely used to build large buildings. Some of the finest cathedrals in Europe were built of sandstone.