Fool's Gold
The term fool's gold is used to describe anything that initially appears valuable but eventually turns out to be worthless. In particular it is used when someone has put considerable effort into attaining the worthless "prize".
So where did the term originate? It turns out to have a very specific meaning.
What Is Fool's Gold?
Fool's gold is the mineral iron pyrite, sometimes just called "pyrite". This is a crystalline form of iron sulphide (FeS2) which has a metallic, golden shine. When seen in a large lump it is obviously not gold, however when a small speck is poking out of a mine wall then the glint can make it look like gold.Many miners used to be fooled by this into thinking they had struck valuable gold deposits. Often considerable time and energy would be spent on mining the area only to discover that there was no real gold present. That said, a little real gold is sometimes found alongside iron pyrite, but that can at best have been a small consolation for the miners who had expected to become wildly rich.
Although iron pyrite looks much like gold it can easily be distinguished from the genuine article. Iron pyrite is less hard and more brittle. Hwever because of its attractive colour it is used in some of the costume jewelry you can buy.
Is fool's gold valuable? Not really. Iron pyrite is one of the world's most common sulphorous minerals and is far from rare. It's main value is industrial as a source of sulphur.