Quite rare, but nevertheless found in all regions of the world, silver is a white, ductile and malleable metal that has been used to make jewelry or as a means of payment for over five thousand years. It occurs naturally with other metals such as gold and in various sulfated ores such as argentite and galena. When exposed to air, oxidation causes silver to tarnish rapidly. For this reason, and also to increase its hardness, silver is often combined with other metals, in particular with gold. Silver gives 18k yellow gold its distinctive color, paler than that of pure 24k gold. Hardness: 2.3.