I can’t even imagine how it was shaped.
Obsidian shears sharply
Ancient alien technology made it possible. I think I learned that from the history channel.
They must have taken a lot of time on each piece. :’)
It grinds pretty easily because it's relatively soft although it fractures readily under pressure or a hard knock. I've cut and polished lots of it, especially iridescent "rainbow" obsidian.
I wish the image of the bracelet was better quality. I can't make out if it's a solid piece or made of tiny tiles. I suspect some sort of primitive lathe was used in its grinding and polishing in order to achieve the precise surface measurements and finish. The concept of the lathe is simple and very ancient. Potters' wheels are a form of lathe.