A beautiful combination of petrified wood and agate is offered by the silicified woods of the Blue Forest in Wyoming. In their pattern they show light to dark-brown silicified wood as well as grey blue and white banded agate.
#Their formation is quite unusual: over an enormous surface in the today's US Federal States Wyoming, Colorado and Utah several huge lakes were formed approximately 42 million years ago. The lakes formed during unfolding the Rocky Mountains in the basins lying between them.
At the water mouths of rivers large quantities of driving wood was deposited. A large part of the woods was covered by carbonat-producing algae. These algae formed a thick layer of carbonates around the trunks and branches. The wood dried and shrank within the coat produced by the algae. Time by time the wood was covered by sediments and began to fossilize. The lake was filled in the course of the time with sediments and ashes from regional volcanos.
Now the actual process of the silification of the woods began. Silica-rich solutions replaced organic substance first by gel-like conditions, second by opalized structures and ended then up in compactly cristallized chalcedony. In the drying fissures and the free-decayed cavities between wood and coat banded agate was deposited. This bluish agate gave the name “Blue Forest Wood” to the fossil wood.