Three native metals

Why does corrosion occur? Anybody have an idea? There are only three metals that exist in nature as metals in a native state. You might have an idea what they are. Gold. Copper. Platinum. Iron is always an oxide — most things are an oxide or sulfide — and platinum is often combined with other things like sulfur. Even silver: silver oxide is not stable at room temperature, but silver sulfide is very stable. That's why silver tarnishes. It's the sulfur in the air that causes silver to tarnish, okay. So silver is always found as a sulfide, iron is usually an oxide, sometimes a sulfide. But in fact most of these metals require a tremendous amount of energy.