Joan Zimbra, age 12, of San Francisco, California, for her question:

How were diamonds formed?

Our wonderful old earth did not form many diamonds and she hid them in unlikely places deep under the ground. She made them from carbon, the same common element she used to make black, waxy graphite. But in diamonds the carbon atoms are arranged in tight, crystal lattices. The diamond is the earth's hardest mineral, many times harder than any other natural mineral. The job of crystallizing those carbon atoms was not easy but earth scientists are pretty certain how it was done.

Energy, lots of energy and power were needed to do the job. It seemed natural to use the fiery fury of volcanic activity and the mighty pressure of heavy layers of the earth's crust. This seems to be the likely recipe because the world's richest diamond mines are located in the vents of ancient volcanos. Perhaps pockets of carbon from ancient coal forests were packed in beds of special clay, cooked in seething heat and squeezed under tremendous pressure. The transformation from common carbon may have been fast or it may have taken ages of time