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'''Araucarioxylon arizonicum''' is an extinct conifer that is the state fossil of Arizona.
In the Triassic period, this species of tree flourished in what is now known as the Black Forest, part of the 378.51 km² (93,492 acre) Petrified Forest National Park in eastern Arizona. Prehistoric Arizona was a flat stretch of tropical turf in the northwest corner of a supercontinent known to modern geologists as Pangaea.
The trees towered as high as 60 m (200 ft) and measured more than 60 cm (2 ft) in diameter. Fossils frequently show boreholes of insects, as well as fossilized hives of prehistoric bees.
The genus ''Araucarioxylon'' is regarded by some paleobotanists as synonymous with the modern genus ''Araucaria'', though this view is not universal.
The petrified wood of this tree is frequently referred to as "Rainbow wood" because of the large variety of colors some specimens exhibit. The red and yellow are produced by large particulate forms of iron oxide, the yellow being limonite and the red being hematite. The purple hue comes from extremely fine spherules of hematite distributed throughout the quartz matrix, and not from manganese, as has sometimes been suggested.

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References

References

★ F. H. Knowlton, New species of fossil wood (''Araucarioxylon arizonicum'') from Arizona and New Mexico, ''Proceedings of the United States National Museum'', 1889.

★ Smithsonian Magazine article on ''A. arizonicum''