Edward Eastman, age 12, of Colonial Heights, Va., for his question:

What art tektites?

These mysterious stones have been called lunar tears. They are not, however, teardrops shed upon the Earth by a weeping moon. They may not reach us from the moon at all. But it is almost certain that tektites fall from the sky and remain on the Earth as grounded space travelers.

If you search in the right places you may come upon a treasure trove of tektites on or in the ground. In many parts of North America there are no tektites, or they are so rare that we never find them. But there are lots of these strange little stones in Texas and our eastern mountains. You might mistake them for the broken scraps of an ancient glass bottle. But experts tell us that the hard and glassy little stones hold dramatic secrets of violent missiles from outer space striking the Earth.

It is almost certain that tektites are meteorites that struck the Earth in ancient times. However, they are unlike the steady showers of average Meteorites that fall from our skies. Bombardments of tektites, it seems, hailed down with tremendous violence and spread over a wide area. A hail of tektites struck parts of North America and Africa some 34 million years ago. Some 20 million years later another bombardment struck central Europe and part of Asia. Australia was struck with a hail of tektites about 700,000 years ago.

We know what they look like and the chemicals from which they are made. But we are not surf about their past history and how they got here. The small stones range from less than an ounce to perhaps a pound. They are made of dark, glassy materials with either smooth or bubbly surfaces. Their colors range from greenish browns through greenish grays to black. They may be round or rod shaped, fat or flat. Some are twisted in odd coils, and some are shaped like mushrooms, complete with stubby stems.

Tektites contain glassy silicas and other common earthy chemicals. But they are unlike any Earth made rocks. Their scorched skin was caused by their fiery fall through the air and experts agree that they did not originate on our planet. They may be fragments from monster meteorites, and one daring theory suggests they came from the moon. Perhaps the lunar craters were caused by the violent impact of meteorites that strewed showers of debris out into space. Some of these flying missiles may have struck the earth with showers of glassy tektites.

The most plentiful elements in our rocks are oxygen and silicon. These elements account for some 70% of tektite material. Tektites also contain oxides of iron and magnesium, calcium, sodium and potassium. The glassy little space travelers are made mostly from the seven or eight most common elements in the Earth's crust. But experts assure us that they were not made in the normal process of rock formation on our planet.