petrified wood
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- fossil
petrified woodPetrified wood from (top left) Coal City, Illinois; (top right) Holbrook, Arizona; (bottom left) Clover Creek, Lincoln City, Idaho; and (bottom right) Arizona.
petrified wood, fossil formed by the invasion of minerals into cavities between and within cells of natural wood, usually by silica (silicon dioxide, SiO2) or calcite (calcium carbonate, CaCO3).
Petrified Forest National Park: petrified woodPetrified logs in Petrified Forest National Park, eastern Arizona, U.S.
Petrified Forest National Park: petrified woodPetrified log pieces in Petrified Forest National Park, Arizona, U.S.
Petrified Forest National Park: natural bridgeNatural bridge in the Blue Mesa section of Petrified Forest National Park, Arizona, U.S.
The petrified forests of the western United States are silicified wood, the tree tissues having been replaced by chalcedony (cryptocrystalline quartz). Often this replacement is so accurate that the internal structure as well as the external shape is faithfully represented; sometimes even the cell structure may be determined.