Formula: Os
Transition metal, platinum group element
Iridosmine is a variety of osmium rich in iridium (all natural osmium contains some iridium) (Mindat).

Specific gravity: 22.48 measured for naturally occurring osmium; 22.61 for the chemically pure element at 20oC; osmium is the densest of all the elements (ChC).
Hardness: 7.0 mohs
Streak: Grey
Colour: White
Common impurities: Pt,Rh,Pd
Melting point: 3030oC, osmium has the highest melting point of the platinum group elements
Boiling point: 5012oC
Abundance in the Earth's crust: 1.5 parts per billion by mass, 0.2 parts per billion by moles, osmium is the fifth rarest element in the Earth's crust (ChC).
Abundance in the Solar System: 2 parts per billion by mass, 20 parts per trillion by moles (ChC).
The most common oxidation state is +4

Igneous environments
Placer deposits

Osmium occurs with other platinum-group elements and alloys, in ultramafic rocks and placers derived therefrom (HOM).
An alloy of 90% platinum and 10% osmium is used in surgical implants such as pacemakers and replacement heart valves (ChC).


At Ruby Creek, Surprise Lake, Atlin Mining Division, British Columbia, Canada, osmium is associated with rutheniridosmine and osmiridium (HOM).

In Russia, osmium is found in many localities, including the Gusevogorskii pluton and the Kytlym and Uktus complexes, Ural Mountains; the Neozhidannyy Creek placers, Tuva; and the Pustaya River placers, Kamchatka Peninsula. Associated minerals include isoferroplatinum, cuprorhodsite, malanite, cuproiridsite, laurite, erlichmanite, cooperite, sperrylite, chalcopyrite and bornite (HOM).

At Fox Gulch, Salmon River - Red Mountain District, Goodnews Bay, Bethel Census Area, Alaska, USA, osmium is associated with bowieite, platinum, iridiumplatinum alloys, laurite and silicate inclusions (HOM).

Osmium-bearing minerals
Mindat lists only 10 mineral species with essential osmium, but considering the IMA approved formulae, in three of these species osmium is not essential, so there are only 7 IMA-approved osmium-bearing species.

Osmium-bearing minerals include:




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