...to mount obsidian in bezel is not trivial. If you really like
the stone very much and wanted to do what it takes, then I would
suggest 22 kt gold for the bezel, or it may not survive.
Will all respect to Leonid, don't let this stop you. I have set
obsidian, and I would say it just requires care. It's not made of
glass, after all... oh, wait, it is. Hmmm. Well, I wouldn't want to
set a stone with sharp corners, but with a fine silver (or 22k)
bezel and reasonable caution, it should be fine. Not really a good
choice for a ring or bracelet, though.