Just like a number of creatures, wood can fossilize too. Wood petrifies in very specific conditions in a two-stage process. The process starts when the plant material is buried under sediments and protected from decay by oxygen and organisms. Then, groundwater rich in minerals and dissolved solids flows through the sediments, gradually replacing the plant material with silica, calcite, pyrite or opal.
The result is as you can see here – a fossil body which often exhibits features of the wood, including the bark and cellular structures. Petrified wood can preserve the original structure of the stem in all its detail, down to the microscopic level. Structures such as tree rings and the various tissues are often observed features.