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Petrified Wood

Arizona State Fossil

Petrified wood log at Petrified Forest National Park; photo courtesy Free Public Domain Photo Database: Petrified Wood.

Official State Fossil of Arizona

Arizona designated petrified wood (Araucarioxylon arizonicum) as the official state fossil in 1988. Araucarioxylon arizonicum is fossilized wood from massive conifers that lived in the Triassic period of prehistoric Arizona (200 - 250 million years ago). All State Fossils

Petrified Forest National Park in northern Arizona protects one of the largest and most colorful concentrations of petrified wood in the world. Made up of almost solid quartz, each piece of petrified wood is like a giant crystal, often sparkling in the sunlight with a rainbow of colors.

Petrified wood is also the state fossil of North Dakota and Louisiana, the state gem of Washington, and the official state stone of Texas and Mississippi.

How is Petrified Wood Formed?

Over 200 million years ago, the original logs were washed into an ancient river system and buried quickly by sediment so that oxygen was cut off and decay was slowed to a process that would take centuries. Minerals such as silica were absorbed into the porous wood over hundreds and thousands of years and crystallized within the cellular structure, replacing the organic material (petrified wood weighs as much as 150-200 pounds per cubic foot).