Rutheniridosmine is a naturally occurring mineral alloy of the elements ruthenium, iridium and osmium with the formula of (Ir,Os,Ru). Rutheniridosmine occurs as hexagonal, opaque, silver-white, metallic grains with a Mohs hardness of six. Platinum, palladium, rhodium, iron, and nickel occur as impurities.^[1]

Rutheniridosmine occurs in association with sperrylite, hollingworthite, iridarsenite, ruthenarsenite, michenerite, laurite, geversite, moncheite, and chromite.^[2]

Type localities include: the Ruby Creek, Spruce Creek, and Bullion mines of British Columbia, Canada and the Horokanai placer deposit, of Kamikawa Subprefecture, Hokkaidō, Japan.^[1]