Todd Anderson, age 10, of Gallup, N.M., for his question:
WHAT EXACTLY IS SAND?
Sand has lots of practical uses. Chemical and glass manufacturers use large amounts of quartz sand for their products. Sandpaper is made by gluing certain types of loose sand onto heavy paper. Concrete and mortar take large amounts of sand for various building and road construction jobs. And don't forget to count the pleasant sandy beaches.
Sand can be a number of different earth materials that are made up of tiny grains of minerals or rocks.
In order to be classified as a grain of sand, the material must be larger than a piece of silt and yet smaller than a piece of gravel. Geologists take their measurements by passing the material through wire screens. The grain of sand must be larger than 1/400th of an inch in diameter and smaller than 1/12th of an inch in diameter.
Most of the grains of sand you find on ocean, lake and river beaches are tiny particles of solid rock that have crumbled. Rocks can break down in many different ways. Some boulders crumble by the action of air, rain or frost. Strong waves also wear away rocks by rolling them over and over and beating against them.
Great amounts of sand can be found on the bottom of seas and in shallow lakes. It is also found on many river bottoms and is often spread by the rivers to lowland areas. In addition, sand can be found along ocean beaches in many different parts of the world.
Greatest amounts of sand can be found in some of the earth's vast desert areas. Here wind shifts the sand and piles it up into huge mounds that are called sand dunes. Scientists believe that deep below some of the dunes are ancient towns and cities that have been buried under the sand for hundreds of years.
Most common type of mineral found in sand is quartz. So Some sand is made up almost completely of quartz grains, although usually bits of other minerals are also present.
On many Pacific island beaches you'll find sand that is made up largely of basalt grains. Basalt is a black lava rock that has flowed from or has been blown out of volcanoes. Other Pacific islands have beaches that are made up of tiny particles of coral and shells of snails and clams which have been broken up and pulverized by the sea's waves.
Precious metals can be found in some river sands. These mineral deposits are called placers. During California's famous gold rush, pioneers took many millions of dollars' worth of gold from placers.
Placers found in rivers in Florida, India and Australia have produced rare metals that are used in jet engines. Platinum, diamonds and other valuable minerals also have been found in the world's far flung placers.