Source : Webster's Revised Unabridged Dictionary (1913)

Iridosmine \Ir`i*dos"mine\, Iridosmium \Ir`i*dos"mi*um\, n.
   [Iridium + osmium.] (Min.)
   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.

Source : WordNet®

iridosmine
     n : 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. [syn: {osmiridium}]