When you hold it up to the light, can you see through it? If yes, then it is Obsidian. If no, it could be flint or chert.
There is also a rock that looks like that with the glamorous name of river rock. I have several of those.
Another test, hold a magnet near it. Is it magnetic?
You could try chipping a bit off of one end -- though it is already pretty small. The outer surface has obviously been rough-polished. There are some types of petrified wood that are black.
It might be a type of hematite. That stuff comes in red and black, and can look like everything from polished metal to a meteorite look-alike.
There is also a rock that looks like that with the glamorous name of river rock. I have several of those.
Another test, hold a magnet near it. Is it magnetic?
You could try chipping a bit off of one end -- though it is already pretty small. The outer surface has obviously been rough-polished. There are some types of petrified wood that are black.
It might be a type of hematite. That stuff comes in red and black, and can look like everything from polished metal to a meteorite look-alike.