Michael F. Brown, age 12, of Lancaster, Pa., for his question:

What are geodes?

Geodes are geological treasure chests. They are hollow pebbles~lined with different minerals, maybe glittering crystals or semi precious stones. The treasure is not discovered until the psbble is opened. A pebble of milky white quartz is worth opening if it seems to be lighter than its neighbors. The walls of its secret cave may be lined with a cluster of amethyst or quartz crystals, clear or smoky gray or rosy pink Another geode may be lined with glowing chalecedony or smooth layers of pastel tinted agate.

These odd stones form slowly in the hollows of ancient rocks. Ground water seeps through the pockets, leaving behind its dissolved chemicals. Slowly the chemical fragments build up layers of minerals insi de the little cave. In time, the rocky little cave breaks free and becomes a geode nodule, stuffed with secret treasure.