Petrified wood is a fossil. Its formation derives when plant material is buried by sediment and protected from decay due to oxygen and organisms. Groundwater rich in dissolved solids then flows through the sediment, replacing the original plant material with silica, calcite, pyrite, or other inorganic materials. The final result is a fossil of the original woody material that often exhibits preserved details of the bark, wood, and cellular structures. 

Petrified wood is found in volcanic deposits and sedimentary rocks at many locations worldwide. It is sometimes found where Volcanic activity covered plant material with ash, mudflows, or pyroclastic debris. It is found where the wood in sedimentary deposits was replaced by minerals precipitated from groundwater.