A noble metal is a metal that is resistant to both corrosion and oxidation when exposed to air. Metals such as gold, silver, platinum, iridium and palladium are such examples. Sometimes, mercury and copper can be regarded as noble metals but some metals like titanium are not even though they are resistant to corrosion. They are known to be very valuable because they are not commonly found in the Earth's crust and have many uses in everyday things from technology to jewelry.