Cheryl McCrary, age 11, Newtown Square, Penna., for her question:

Is petrified wood a mineral?

The word mineral covers a multitude of things. Gold is a mineral and. so is water. Every stone on the face of the earth is a mineral of some sort. h substance must have two qualities in order to be a mineral ‑ it must be inorganic and it must be found in nature. The word inorganic is the opposite of organic and organic means anything living or any part of a plant or animal which once lived. So, a mineral is one of Nature's substances which is not part of a living organism and never was,

Petrified wood is wood which has turned to stone. Wood, of courses is not a mineral. On the other hand, stone most certainly is a mineral. This leaves us with quite a problem. So let's try some detective work and figure out the answer for ourselves.

The story begins millions of years ago, when massive trees grew in what is now our western desert and prairie land. The climate was moist in those far‑off days, damp enough to support huge forests. This friendly climate changed, perhaps suddenly in the northern regions and more slowly in the south, We know of at least one forest in the State of Washington that was burned and buried beneath volcanic ash.

To the south, in Arizona, there was at least one log jam where a gushing river carried away countless fallen trees. The river dried up and the fallen trees laid buried under the blowing sands. Here, and in the northern regions, were masses of buried lumber which normally should have decayed, broken up and returned its chemicals to the soil. But this did not happen, most likely because there were no decay bacteria in the soil.

Through millions of years the buried wood was  first seeped in water and then dried out, time after time. This busy water dissolved and toted along all kinds of chemicals on its way through the ground. It went to work on dissolving the fallen trees and did so, particle by particle. But the water was so loaded with ground chemicals that for every particle of wood it toted away it had to leave behind a particle of its chemicals.

Bit by bit, through millions of years, the original wood was replaced by stone. The types of stone in petrified wood are usually silicas. There is jasper, onyx and glowing opal. Often these semi‑precious stones are tinted with iron and other substances present in the soil. The colors of some petrified wood challenge the rainbow.

Under the microscope you can see the cell structure of the original wood. In replacing the wood with chemicals, fragment by fragment, the original design of the wood. was copied. But none of this original wood remains. Petrified wood is made by Nature solely from non‑living chemicals and is, therefore, a mineral.