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This is osmium.

Symbol Os
Atomic number 76
Atomic mass 190.2 amu

Osmium, osmium and its companion metal iridium were discovered in 1803. The discovery was made when a black, metallic substance always appeared when crude platinum was treated with aqua regia. Most people suspected it to be graphite. But when the black residue was examined, it was concluded that it must be a new element instead of an allotropic form of carbon. Upon closer analyses, it was determined that there were two new elements in the black residue. One of them was named iridium because of its array of compounds. The other was named osmium because of its nasty smell.

Distinguishing properties

Osmium is extremely hard, and is one of the heaviest elements with a density about twice that of lead. It is a lustrous metal, but a thin film of oxide, which emits highly toxic and odorous gases, forms on the exposed surfaces. Because of the severely toxic properties of osmium oxides, there are few commercial applications of the element itself.


Osmium is usually found in the company of natural platinum. It is also found in large quantities in the nickel ores in Sudbury, Ontario. Therefore, osmium is recovered as a byproduct of the mining and refining of platinum and nickel.


Osmium can be used safely as an alloying agent. The alloy is extremely hard and is used where frictional wear must be minimized. Pen tips and gramophone needles are 60% osmium. The alloy is also used in electrical switch contacts.

See also

Periodic table of the elements