The noble metals are metals that are resistant to corrosion and oxidation in moist air, unlike most base metals. They tend to be precious, often due to their rarity in the Earth's crust. The noble metals are most commonly considered to be ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, and gold.
Other sources include mercury,rhenium or copper as a noble metal. On the other hand, titanium, niobium, and tantalum are not included as noble metals, although they especially resist corrosion. Noble metals should not be confused with precious metals (although many noble metals have high value).