Osmium is a transition metal that has the atomic number 76 and the symbol Os. It is one of the densest elements, with a density of 22.59 g/cm³. Osmium has a bluish-white color and is very hard and brittle. It is primarily used in alloys with other metals, such as platinum, to make them harder and more resistant to wear and corrosion. Osmium is also used in electrical contacts because it is a good conductor of electricity and has a low contact resistance. In addition, osmium is used in fountain pen tips because it has a high melting point and is very hard, which helps to prevent the tip from wearing down too quickly.