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Petrified Log Wheel

© Copyright 2002, Jess Stryker.  CC-BY-4.0 License.
Petrified Log Wheel.  Petrified Forest National Park, Arizona.
Although they look like logs (and were once logs) they are now solid quartz rock.  Essentially they are huge crystals.  The color comes from impurities in the quartz, like the rust red of iron, and various shades of black caused by carbon.  Apparently the core of this log either never became rock or became a softer rock that eroded away leaving a hole.  Another possibility is that the center was an attractive crystal and was chipped out by gem collectors.

See my other petrified log photos for more on petrified wood formation and how it got here in Arizona, miles from the nearest forest!