Nice piece of rock containing a geode. Thanks for lots of pictures to help viewers. Fossilized wood normally has some visual evidence of a cellular structure, even though the cells are usually mineral-filled. I don't see that in this case. My guess, as a naturalist but not geologist or minerologist, is that it is a thick vein of quartz that has had softer rock worn away from it, leaving this piece and the wearing process has rounded the edges of this piece. Maybe a real expert on the subject will weigh in.