Arizona State Fossil
Petrified Rainbow Wood (common name)
Araucarioxylon arizonicum (scientific name)
Araucarioxylon arizonicum, sometimes called "rainbow wood," is a colorful type of petrified wood formed from an extinct tree that once grew in Arizona. In mineral terms, petrified wood is chalcedony, which is microcrystalline quartz. The quartz has replaced all the organic material of the wood. Quartz crystals are colorless, but the elements manganese, copper, chromium, cobalt, carbon, and iron give petrified wood its color. The variety of colors includes red, orange, yellow, green, blue, pink, and black. Petrified logs tend to look as if they were cleanly cut because the physical characteristics of cylindrical quartz cause them to break cleanly when stressed.
Petrified Forest National Park in northeastern Arizona makes the state famous for this fossil. It is generally accepted that this park, also a national monument, contains the most colorful examples of silicified logs in the world. The park mainly contains examples of the species Araucarioxylon arizonicum.
This wood is the petrified remains of large trees that grew in the warm climate of Arizona during the Triassic Period. About 200 to 250 million years ago, the logs in the area washed into an ancient river system and were buried quickly and deeply by massive amounts of sediment. Minerals, including silica dissolved from volcanic ash, absorbed into the porous wood over hundreds and thousands of years. They crystallized within the cellular structure, replacing the organic material as it broke down over time.
Petrified wood occurs in every county in Arizona, but commercial production is essentially from privately owned lands in Navajo and Apache Counties near the national park. In 1988, the Arizona legislature designated Araucarioxylon arizonicum the state’s official fossil.
Petrified wood is the official gemstone of the state of Washington. Various types of petrified wood are the state fossils of North Dakota, Arizona, and Louisiana. Petrified palmwood is the state stone of Texas. Alberta, Canada, has also designated petrified wood its provincial stone.
DISCOVERY AND NAME ORIGIN
In 1889, F.H. Knowlton gave the name Araucarioxylon arizonicum to petrified logs found in Arizona. Noting similarities to the present-day genus araucaria, he named the genus araucarioxylon; the -xylonsuffix is used in naming fossils that resemble modern genera. Recent research indicates that the three logs Knowlton examined probably were of different genera.
The word "petrified" comes from the Greek root petro meaning "rock" or "stone"; petrified literally means "turned into stone."
Wood becomes petrified when it is buried underground in sediment by volcanoes, mudslides, or other natural disasters. As groundwater passes through the sediment, minerals such as silica, dissolved from volcanic ash, are deposited in the wood. As the plant’s lignin and cellulose decay away, the silica hardens into quartz crystals. Petrifaction often maintains the structure of the wood. This may include tissues and tree rings, although they are not annual tree rings based on seasons and therefore cannot be used to determine the tree’s age. The process of petrifaction usually takes less than 100 years.
Petrified forests are widespread. Petrified Forest National Park in Arizona is the largest in the country and contains what may be the largest concentration of petrified wood in the world. Another very large U.S. deposit of petrified wood is found in Theodore Roosevelt National Park in North Dakota. The Petrified Forest National Monument in Chubut Province, Argentine Patagonia, is another of the world’s best petrified reserves.
Because of chalcedony's abundance, durability, and beauty, early humans made weapons and tools from many varieties of chalcedony including agate, agatized coral, flint, jasper, and petrified wood. The earliest recorded use of chalcedony was for projectile points, knives, tools, and containers such as cups and bowls.
Petrified wood material is suitable for tumble polishing for use in baroque jewelry or for cutting into cabochons for jewelry and display. Freeform and calibrated slabs are polished for pen and pencil set bases and bases of other items, and polished slabs are used for clock faces. Additionally, large blocks, limb sections, and geometric shapes are used as bookends and decorator pieces. Objects of art, principally carvings, are produced, and furniture such as coffee tables and end tables are made from petrified wood.
Scientists at a laboratory in Washington state created artificial petrified wood by soaking pine in silica and tungsten solutions.
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|Author: World Trade Press|