This is a part of an opalized tree, and the rings you see are actually tree rings; or at least they were.
This is an very rare sample: opal can be fairly common in petrified wood, but this is a fire opal, which makes it so much more valuable. Fire opals are transparent to translucent opals with warm body colors of yellow, orange, orange-yellow or red – basically, it often has pretty colors.
So how did this magnificent opalized tree came to be? Initially, water filled the cracks and empty spaces of the source fossil, and the silica content in the water hardened and turned into opal or chalcedony.
Andrei is no scientist, but from an early age, he has been fascinated by science; that's why he went to college, and signed up for Geophysics. Feeling that there's a huge gap between science and average people, he rallied TP, started ZME Science, and gave it a green twist too. 
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Published on Tue, Nov 12, 2013 by Mihai Andrei
Post filled in: GeoPicture