Wikipedia:POTD column/September 16, 2006

A petrified log in Petrified Forest National Park, located in northeastern Arizona, USA. The pieces of wood found in the park are mostly of the extinct species Araucarioxylon arizonicum. The logs were buried under volcanic ash, which was the source of the silica that helped to permineralize the buried logs, replacing wood with silica, colored with oxides of iron and manganese.

Photo credit: Moondigger
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