Geology And Geophysics
Petrified Logs at the Petrified Forest National Park

Petrified Wood Formation



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Petrified Logs at the Petrified Forest National Park
Stephany Mccann's image for:
"Petrified Wood Formation"
Caption: Petrified Logs at the Petrified Forest National Park
Location: 
Image by: Petrified Forest Ranger
© Attribution 2.0 Generic http://www.flickr.com/photos/petrifiedforestranger/6083540240/in/photostream/

Petrified wood is a form of fossilized plant, often trees, which is created both naturally and in labs. Samples are typically millions of years old, and formed due to nearby volcanoes which supplied the ash and silica needed for petrification. One of the largest collections in the world is located in the United States at the Petrified Forest National Park.

-Natural Formation-

The process of petrification is simple:

*Wood or similar materials are covered with sediment (volcanic ash, lava flow, landslide, etc.)

*Water rich in minerals passes through the sediment (ex. Silica)

*Minerals from the water are deposited in the plant cells

*Plant’s lignin and cellulose decay over time

*Stone cast of the wood remains

According to the Petrified Forest National Park, petrified wood is “very hard (7.8 on the 1-10 Moh scale!), but brittle.” It’s composed primarily of silica, or quartz, which breaks cleanly. When the logs crack post-petrification due to stress, they are still ensconced in the minerals; upon decaying the breaks widen and thus the logs “look like someone cut them with a saw.”

Petrified wood is also heavy, weighing in at around 160-200 pounds per cubic foot, and is valued both as a semi-precious gemstone for jewelry and as an ornamental material for furniture and other household items. Its age also gives it importance, giving scientists a resource for fossils and information from time periods that are millions of years past.

-Lab Formation-

The lab-synthesized version, which exponentially hastens petrification from millions of years to a few days, was pioneered by Yongsoon Shin and his colleagues, who did their work at the Pacific Northwest National Laboratory.  

Their process of recreating petrified wood involves slightly more effort:

*Pine and poplar lumber is cleaned and cut into cubes

*Soaked in hydrochloric acid and silica solution for two days each

*Air-dried

*Placed in a furnace containing argon gas

*Gradually heated to 1400 degrees Celsius for two hours

*Cooled to room-temperature in an atmosphere of argon

This mimics a specific type of petrification, known as silicification, is what gives petrified wood its stone-like appearance. The end result of the experiment is silicon carbide, and Shin suggests that with the wood’s “porosity and high surface area . . . it could be particularly useful for filtering or absorbing pollutants or other chemicals.” These large surfaces are due to the vast and intricate network of channels and pores in plants, in which a single gram of material flattened to a sheet could cover a football field.

-Conclusion-

Petrified wood is created from an interruption of the decay process with mineral-rich sediment, either naturally or human induced. The process of petrification is typically slow and results in a stone cast of the original wood log, useful for both decoration and scientific research.


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ARTICLE SOURCES AND CITATIONS
  • InfoBoxCallToAction ActionArrowhttp://www.nps.gov/pefo/index.htm
  • InfoBoxCallToAction ActionArrowhttp://phys.org/news2801.html
  • InfoBoxCallToAction ActionArrowhttp://www.nps.gov/pefo/faqs.htm
  • InfoBoxCallToAction ActionArrowhttp://www.livescience.com/110-presto-instant-petrified-wood-created-lab.html