iridosmine(n = noun.substance) osmiridium - a hard and corrosion resistant mineral that is a natural alloy of osmium and iridium (usually containing small amounts of rhodium and platinum); used in needles and pen nibs etc.; Array
The native compound of iridium and osmium. It is found in flattened metallic grains of extreme hardness, and is often used for pointing gold pens. [1913 Webster]