Ditto on the petrified wood statement, looks like a "hit". Whether it was used for anything I would not venture a guess - but think petrified wood is "cool" especially if it has "knots" in it; but then I keep "pretty rocks" just because they are neat, and someday will have to build a 'pretty rock' cabinet - if I had found that I would definitely keep it, but to add to the rock collection, not as an artifact.
Oroblanco