Doubt anyone would be able to ID the wood, but it is a nice piece. As for waiting for it to sink... it is likely that it eventually will, but not every piece of wood will eventually sink, either. I have a big chunk in my oscar tank that I keep down with rocks stacked on top, and I that I got from a friend who kept it floating in a turtle tank for years before I got it. It still floats. Rocks on top is a bit risky, because if it gets shifted it can pop up and dump the rocks, which can hit the glass... I would be tempted to try the slate method for that one...