Lynn Smith, age 13, of Peoria, 111, for her question:

What is opal made of?

Sparks of glowing colors seem frozen in these glassy stones, Some opals favor flame colors of red and orange. Some display flecks of vibrant blue and green, The precious black opal is a glowing pool of jets and charcoal greys. The most common opal is the milky fire of delicate pastels.

Yet like all precious stones the opal is made from simple elements. Most of it is silicon and water. Silicon is one of the most common of elements. It goes to make sand, quartz, agate, flint and jasper. In opal minute fragments of silicon have mixed and gelled with minute particles of water. The radiant colors are merely impurities in the mixture.

Some of the lovliest opal is in petrified wood. Here water loaded with silicon has replaced to wood of ancient trees, particle by particle.