posted on Jul, 30 2011 @ 04:18 PM
I thought I would toss out the possibilities of tektite, or moldavite, which are essentially glass formed from the impact of an object from space.
While moldavite is typically a dark green, I have seen specimens which were mostly black. It's vitreous, or glassy. (Well, it is a form of
glass). Tektite is usually pitted, but again, can sometimes be smooth. So. Does it have any green in it if you hold it up to the light? Also, use
a magnifying glass if you don't have a jeweler's loupe. You can google each one for pictures.
If you can rule out tektite or moldavite, then I agree it's obsidian. Obsidian is nice, and is sometimes used in jewelry. Keep it, and if it were
me, I'd return to see if I could find some more.