Sounds like mopani. I have several pieces of it; it's much heavier/denser than driftwood and is actually two colors (light outside, dark inside). Zoo-Med is usually the company that I've seen selling it.
I haven't had it long enough to know if it will soften as quickly as the driftwood I have, but I suspect it will last much longer. It sinks fairly quickly and like corkbark and driftwood, it does release tannin, so I don't know how it wouldn't change the water chemistry, at least until tannin stops being released. Tannin is what makes the water brown/tea colored, but is not a bad thing and will actually make the water a little more acidic. I've never noticed any smell. You can minimize the amount of tannin that's leached into the tank by presoaking the corkbark/driftwood/mopani and changing the water until the color doesn't change much. I've done this, and I've also just rinsed the piece and put it in the tank and done partial water changes until the water stopped turning really brown. Some pieces release more tannin than others.
It made great basking areas for the snappers I was caring for, and looked really nice when algae started growing on it. Now that they're gone, I'm going to disinfect the pieces in diluted bleach, rinse and let them dry for a good while so they'll be ready for someone else.
I've never paid $20 for any of the pieces, but if I saw a "perfect" piece, I'd be tempted.
"You become responsible, forever, for what you have tamed." -Antoine de Saint Exupery-
Posted: Tue Sep 01, 2009 1:25 pm 