Osmium tetroxide (also
osmium(VIII) oxide) is the
chemical compound with the
formula OsO
4. The compound is noteworthy for its many uses, despite the rarity of
osmium. It also has a number of interesting properties, one being that the solid is
volatile. The compound is colourless, but most samples appear yellow. This is most likely due to the presence of the impurity
OsO2, which is yellow-brown in colour.