Fossil trunk

For a tree trunk to turn into petrified wood, there are several ways this can happen, and they involve different chemicals. For petrification to occur, the wood must be able to interact with the petrifying substance, causing it to precipitate from an aqueous solution. Through a process of fossilization, a piece of trunk unites itself with elements such as silica, calcium or pyrite. Silica is a water-insoluble solid. Silicification is the penetration and fixation of silica in the organic material that will serve as the basis for the formation of the fossil. In the petrification process, silicic acid molecules pass from the aqueous solution to the surface of the molecular constituents of the vascular tissue of wood. As silicic acid builds up inside the wood, its molecules begin to fuse. The continuation of this process leads to the formation of a silica film around the cell surfaces, reproducing the histological characteristics of wood. Because of this, silica petrification is able to preserve an impressive wealth of detail not observable in other types of fossilization. The petrification of wood depends on the existence of a reasonable amount of silicic acid in solution. Silicic acid is generated from silica in an acidic medium, and most natural reservoirs of water are not acidic enough to hydrolyze an appreciable amount of silica. It is very common for petrified wood to be found in volcanic regions, particularly if an eruption occurred around the time the wood was buried.