This petrified tree is within Yellowstone National Park. It is still standing (unlike most petrified trees which have long fallen). It has an interesting texture which reminds me of dried wood. All of the organic matter has been replaced by minerals--this is what is called petrification.
Taking this picture required considerable body contortions on my part, because the tree is completely surrounded by a fence of iron spear-like posts--each with an arrowhead-shaped tip facing upward. To take this picture, I had to get almost flat against the ground and aim the camera upward between two of the fence posts. The picture was taken at 1/100 sec at f/5.6 aperature.