Karen Ryan, age 10, of S. Portland, Maine, for her question:

What makes sand?

Wind, weather and running water are always at war with mountains, rocks and boulders. It takes long ages of time, but eventually the hardest rock can be broken into fragments by these forces. If the rock is very durable, some of its fragments will become grains of sand. If the rock is not so durable, it will wear away to dust and powder.

Only the toughest rocks get to be grains of sand, The; hardest of the common rocky minerals is quartz. Most sand contains some quartz grains. Some sand is almost all quartz. The sand on your favorite beach also may contain grains of feldspar and mica. Some sands contain grains of ancient seashells. And some contain grains of garnet and of gold. The sands of White Sands Desert are composed almost entirely of gypsum.

These sand‑making minerals are tough enough to endure long ages of hardship. Any pail full of sand is likely to be a mixture of these minerals. Soma of the grains will be of one sort, some another. The grains may be of assorted sizes or of more or less the same size. Large grains may be almost pea sized. Small grains may measure as many as 500 to the inch.

Most sand is on the move, carried by wind or water. The desert wind lashes through canyons and around the mesas. It moves loose stones. They crash into rocky surfaces, breaking off morn stones. The stones and pebbles are broken into smaller and smaller fragments until they become grains of sand. The lashing winds hurl this a.and at the faces of boulders and cliffs, polishing them smooth and chomping more rocks into grains of sand.

Water also breaks up rocks and boulders. It tends to dissolve the softer minerals in a rock, leaving the harder minerals to chip off in fragments. Running water goes to work on the jagged fragments, wearing them smooth. Some of them become stones and pebbles, tossed and tumbled by the gurgling streams.

As the rushing waters hurry them along, the pebbles bump and crash into each other. They break apart and the sturdiest fragments become grains of sand.

Granite is a mixture of minerals, often riddle. with small crystals of quartz. Through ages of hardship, most of the granite minerals :nay wear away. But not the tiny crystals of quartz. When all else has gone, these little crystals are left as grains of sand. A good deal of the world’s quartz sand was formed in this way.

Wind is harder on the sand‑making minerals than is water. It tends to smooth the rough edges of the gritty grains. Desert sand, as a result, is usually fine. This is the fine, free‑flowing sand we use in hour glasses. As a rules smooth sands are older and have traveled farther. Gritty sands have not suffered enough hardship and buffeting to have their sharp edges worn smooth.