Is it rootwood, all gnarled and cool looking?
If so, yeah, it sinks easily and it's great looking in a tank.
BUT ...
Soak and boil it a whole bunch first, especially if you don't want it to (harmlessly) discolor your water slightly.
Also, if you use more than a small piece, you'll want to regularly check your ph over the coming months to be sure the tannins leaching out don't cause a major drop.