This element is no longer available.
Osmium is lustrous, silvery metal, one of the so-called platinum group of metals. It is the densest metal known, although only by the narrowest margins. Osmium is unaffected by water and acids, but dissolves with molten alkalis. Osmium powder reacts slowly with the oxygen of the air and gives off detectable amounts of osmium tetroxide vapour.
The metal is used in a few alloys and in industry as a catalyst. At one time it was to be encountered in the nibs of high-quality fountain pens, compass needles, long-life gramophone needles and clock bearings, thanks to its extreme hardness and corrosion resistance.