Osmium

Osmium is a hard, brittle, blue-grey metal of the platinum family of metals and is the most dense naturally occuring element. It is a chemical element with the symbol Os and atomic number 76 in the periodic table. Osmium is typically found as an alloy in platinum ore. 

Due to the extreme toxicity of its oxide, osmium is very seldom used uncombined. Instead, the metal is often alloyed with other metals that are used in high-wear applications. Osmium alloys such as osmiridium are very hard and is used in devices that need to resist wear from frequent use. Hence, osmium alloy is used to manufacture items like fountain pens tips, phonograph needles and electrical contacts.