Petrified wood is formed when the wood is submersed in water containing minerals, which eventually take over the wood's organic matter, creating a fossil of stone.
The process of wood being turned into stone is called permineralization. All organic matter is removed, but the original structure of the stem tissue remains. Waterlogged wood in sedimentary water becomes preserved due to the lack of oxygen in the water. Minerals in the water flow through the wood and take over the structure as the organic components begin to decay. The minerals make an exact replica of the wood's fibers and cells, creating a stone mold over the wood.
The mineral most often associated with wood petrifaction is quartz. Opal, calcite and carnotite can also be found in petrified wood. The process of permineralization of wood takes a few years but lasts millions. The beauty of the color and intrinsic quality of petrified wood make it valuable in jewelry, paperweights, and other decor. It can be cut and polished or left in its natural state. There are forests of petrified wood in various parts of the world. Petrified Forest National Park in Arizona has stone logs that are more than 160 million years old.