Platinum is a transition metal with high density, extensibility, silver color, metallic luster, hardness of 4-4.5 and relative density of 21.45. The melting point is 1773℃. It is highly corrosion resistant- the metal does not oxidize in air at any temperature.Platinum and platinum alloys are used in a wide range of settings where chemical inertness or wear resistance are important, including medical devices, laboratory instruments, electrical contacts, spark plugs, and turbine engines. A platinum-iridium alloy was also used to produce the international prototype kilogram and meter in the late 19th century; of the two only the kilogram remains in official use. Finally, organometallic platinum complexes have been investigated for use in cancer treatment. Like other platinum group metals, platinum is most often obtained for commercial use as a byproduct from nickel and copper mining and processing, but can also be obtained from rare platinum-rich ores and alluvial deposits of native platinum.