I would like to know if rough pyrite nugget like beads safe to use in beaded jewellery?
I guess that would depend on what the definition of “safe” is.
Pyrite nuggets may contain traces of arsenic, nickel, or copper, and they also break down over time. You should wash your hands after handling them. Since it’s likely the wearer will handle the beads of a necklace, I think it would be wise not to use pyrites as “raw” beads. On the other hand, a pyrite piece mounted on some backing might be a better option for a necklace, maybe as a pendant, but I’m not sure that would be practical for necklace beads.