Osmium tetroxide has a strong odor resembling chlorine and rotting raddishes.
It is also highly toxic. Powdered osmium will oxidize easily in air at room temperature, producing the odorous tetroxide, unlike its neighboring noble metals. Osmium's high hardness makes it a valuable alloying agent for parts that require high wear resistance, such as gold fountain pen nibs. Through Chemistry of the Elements by N. N. Greenwood, A. Earnshaw Greenwood and Earshaw is an excellent inorganic chemistry text as well as a valuable reference for the chemist or geochemist. Their systematic treatment of the elements by group within the periodic table makes for a coherent treatment of periodic properties.