Mountain Laurel wood

http://www.aspca.org/pet-care/animal-poison-control/toxic-and-non-toxic-plants/laurel

Toxic to mammals (That link is for dogs, cats and horses) so I would try some in a test tank with some sacrificial fish.
Make sure it is really well aged, dead for a year or more, and alternately exposed to soaking rain and drying sun. This usually breaks down toxins.

I should have looked up toxicity. Which I did after I read your post. It is also toxic to fish, at least the leaves, twigs are. It seems too risky.
Thanks.

I grew up on the East coast, and we were always told not to burn it in campfires, as the smoke would be toxic.

So, I'd be pretty hesitant to use any of it in a tank. might work if it's really well weathered, but I'd probably just as soon try another source of wood.