Malinda BouEy, age 9, of Newport, Ore., for her question:

What are agate stones?

Agate stones are made of quartz, the hardest of the many minerals, which make up the Earth's pebbles and stones, sands and gravels. The finest of the quartz stones are called chalcedonies, and agate is one of these smooth and waxy chalcedony stones. It is formed by fragments of dissolved quartz left behind by seeping water.

Some chalcedony is glassy clear, and some is tinted with foggy smudges of white or gray, blue or brown. Agate chalcedony is adorned with bands of rainbow colors. The colors may be arranged in flat stripes or round circles, one inside another. Sometimes the bands are wavy stripes that look like frozen ripples of colored water. The eye catching colors in the agate were caused by impurities mixed with the fragments of quartz when the stone was being built, layer by layer.