Osmiridium sand. Pile of small pieces of osmiridium. Osmiridium, or iridosmium, is a natural alloy of osmium and iridium, with traces of other platinum group metals. It may be found naturally or man-made. Osmiridium contains about 50 percent iridium, while iridosmium contains about 70 percent. It is very rare, but can be found in mines of other platinum group metals.