4.4" Petrified Wood (Schinoxylon) Section - Blue Forest, Wyoming

It was formed when trees died and fell into a swamp where they were rapidly covered by algae. This formed casts that preserved the original bark surfaces and kept the trees from decaying. Eventually the algae casts and the spaces between them were filled in by minerals, often in exquisite, crystalline form. A paper on the formation of this petrified wood can be found at the link below.

Mineralogy of Eocene Fossil Wood from the "Blue Forest" Locality, Southwestern Wyoming, United States