Jeff Phillips, age 11, of Winston Salem, N.C., for his question:

WHAT ARE TEKTITES?

Every rock collection deserves at least one tektite. The glassy little stone may be dark green or brown or even black. It may be shaped like a teardrop, a ball or a button, a disk or a dumbbell. In any case, it is a geological wonder ¬and no scientist is certain about how it came to be. obviously its glassy structure reveals a fiery past and its twisted shape suggests a fast spin through the air.

Scientists suggest three possible theories on how the tektites were formed. Perhaps they were gobs of molten material caused by fiery impact when a monster meteorite struck the earth. Perhaps they were born on the moon, when giant meteorites whacked down on the lunar landscape. Some of the molten material may have been tossed way out into space and landed as tektites on the earth. Other scientists suggest that larger chunks of such lunar material may have circled the earth before breaking up and falling down as tektites.