This is a piece of opalized wood from the late Miocene Neroly Formation near Antioch, CA. AKA Antioch Wood. What is the cause of the herringbone or chevron growth rings? Did the tree grow that way or was the wood compressed before it was fully mineralized? I found similar wood from Late Miocene formations in the Berkeley Hills. I also have seen similar wood from the Hell's Canyon area in Idaho/Oregon. Has anyone found wood with a similar pattern elsewhere?
Any idea what type of wood this is?
The field of view in the photo is about 0.6 inches across.