Claire Skidmore, age 13, of Montreat, North Carolina, for her question:

Do rocks freeze?

When we think of freezing, we tend to think of ice, which is the solid state of water. If we warm it to 0 degrees centigrade, it melts to its liquid form and when heated to 100 degrees centigrade, it becomes gaseous vapor. The solid, liquid and gaseous forms of water depend on temperature. The same rule applies to rocks and most other substances. However, each substance has its own freezing and melting points  ¬at which it changes from one form to another.

The rocks of the earth's crust happen to have melting points that are much higher than normal temperatures. These are the critical points at which solids melt to liquids and liquids freeze solid. Hence, under normal conditions, all the earth's rocks are frozen solid. However, all of them may reach their freezing melting points in the seething heat of a volcano. Then the solid rocks melt and become molten lava.