Hard to say what it's made of from pics, but I doubt that it's copper or any of its alloys. Copper, brass and bronze will all patinate green over differing amounts of time.
Not sure of what that is, as stated copper would have turned green an I don't think it is hematite because you can see the colors of what brass will turn and with you saying it is hallow, then NA did not make hallow cast beads. It may be a trade item