Petrified Wood

Petrified wood is a fossil formed when buried wood is replaced by silica, chiefly microcrystalline quartz and chalcedony (SiO₂), preserving the original cellular structure in stone. Petrified wood forms through permineralization, a process where organic wood tissue is gradually replaced by minerals (typically silica) while preserving the original cellular structure. When a tree is buried rapidly by volcanic ash, sediment, or flooding, it enters an oxygen-poor environment that prevents normal decay.

Mineral-rich groundwater then percolates through the wood, depositing silica (and sometimes other minerals) in the cellular spaces. Over thousands to millions of years, the organic material is entirely replaced, cell by cell, by quartz, chalcedony, or opal. The replacement is so precise that tree rings, bark texture, and even individual cell walls can be preserved in exquisite detail.

Different minerals create different colors: iron oxides produce reds and browns, manganese creates pink and black, copper creates green and blue, and chromium can create vivid greens. Arizona's Petrified Forest specimens are roughly 225 million years old (Late Triassic), preserving ancient Araucarioxylon trees.

Petrified wood is identified by its stone composition combined with preserved wood grain, tree rings, and bark texture. It looks like wood but feels like rock, with the weight and hardness of quartz. Under magnification, you can often see preserved cellular structure.

Distinguish from natural wood (petrified wood is far heavier and cold to the touch), agatized coral (different growth patterns), and other fossils. A simple test: it won't burn, scratches glass, and shows conchoidal fracture on fresh breaks rather than fibrous wood fracture.