Alexander Kerr, age 10, of Stratford, Conn., for his question:

How is sandstone formed?

Sandstone is one of the world's showy rocks. It dresses the desert hills in sunset colors. It streaks the colors of deep canyons in shades of red, yellow, brown wind grey. Sometimes it is sandy colored and sometimes almost white,

Every block of sandstone had a long and very adventurous life.  In it’s first form it was here when the world was very, very young. In fact, it began as one of earth’s  oldest rocks. These are the igneous or fire‑formed rocks. Among them is a hard mineral called quartz.

Maybe you have found a milky white quartz pebble on a beach. Try a teat for hardness on that pebble. Scratch it on any other kind of atone you can find. The quartz will leave a scratch on the other stone .‑ unless the other stone is a diamond, ruby or other precious or semi‑precious stone. No ordinary stone can scratch quartz back. For quartz is the hardest of all ordinary stones.

Yet even tough quartz can't take a beating through the ages. Centuries of pounding waves, heaving tides and desert winds can chomp it to bits. Much of it ends in small, gritty grains. For most of the sand on the beach and in the desert is made o f powdered quartz stone. The first chapter in the life of a slab of sandstone ended when the original quarts stone became sand.

The first adventure was a chomping up ,job taking millions of years. The second adventure was a glueing together ,job, also taking millions of years. This job required water‑and cement. A stretch of sand may have become swamped with a shallow sea. A busy stream may have toted tons of sand down to an ocean. In any case, the sand found itself under fairly calm water. For it settled and sank in layers to the bottom.

Also mixed in the crater were muds and soft clays. These also sank and mixed with the sand. Some of the soft mixes contained forma of iron. Some were full of lime and some contained an element called silica. Deeper and deeper  the layers of sand and silts as more sediment was toted into the quiet waters.

In time, the fine clay acted as a cement and glued the gritty grains of sand together. Pressure from above formed the whole mass into solid slabs. It only remained for the water to drain away. The mixture of sand and silt became a dry, sedimentary rock ‑ formed from sediments of mud and powdered stone,

The colors of sandstone depend upon the kind of cement used to glue the golden grains together. Iron oxides In the clay tend to produce handsome hues of red, brown and yellow. Lime mixed in the cement tends to form sandstone of grey and whitish tones. Some sandstones may go one step further in its life history. It may become a very hard stone called quartzite, But only sand cemented with silica can become quartzite.