Rita Powers, age 12, of South Burlington, Vt., for her question:

WHO DISCOVERED SILICON?

A Swedish scientist named Jons J. Berzelius discovered silicon in 1923. Silicon is a dark gray, hard chemical element. Except for oxygen, it is the most common element in the Earth's crust.

Silicon makes up the major portion of clay, granite, quartz and sand. Silicon compounds have many uses. Silica, which is silicon dioxide, is a principal ingredient in glass. Silicon carbide, one of the hardest substances known, is used to grind and polish other materials.

Silicon is used in the manufacture of transistors because, among other reasons, it withstands heat well and is relatively inexpensive.