Petrified Wood

Arizona State Fossil


Petrified wood log at Petrified Forest National Park AZ

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).

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 a state symbol of Texas, Louisiana, Mississippi, North Dakota, and Washington state. All State Fossils

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). 



Araucarioxylon arizonicum; petrified wood from prehistoric Arizona; official state fossil. Photo by beautifulcataya on Flickr (noncommercial use permitted with attribution / no derivative works). All State Minerals

Araucarioxylon arizonicum - petrified wood from prehistoric Arizona

Petrified wood log; photo from free public domain

Petrified wood log


Rock hounds digging rainbow petrified wood Arizona