Then the best way to make sure it is okay is to throw it in some water (not the tank yet, of course!). You'll want to soak it in some water, boiling or otherwise, and see what happens. With woods like Mopani, which are rich in tannins, I don't soak these. I just rinse with scalding water and then place in the tank. But this suits the types of aquariums I keep. Because this is a mystery wood (and I pic may be helpful, maybe someone can ID it for you??), I would soak it for a while, rinse it with hot water, basically do what Dom said. If the wood feels mushy or soft in any place, discard the wood because it is rotten and will decay in your tank and cause problems.