In our way back from the Valley of Kings, we stopped in a stone factory with some appealing statues in its front, where we bought a wonderful head in lapis-lazuli (not cheap). As a reward, the owner offered my kids two necklace of small beads, also in lapis-lazuli - he said and... it seemed.
They had it on when diving in the pool, back to the hotel, and, suddenly... the miracle! The lapis-lazuli beads were gone, the kids had only the string on their necks. Of course, the beautiful beads where... plaster.