Pyrite is a very common mineral. Due to its yellow color, it is called fools gold because there was time when miners confused it with gold. Pyrite is often used in ornaments and jewelry. Jewelry made out of fools gold is called Marcasite jewelry. It makes it very confusing because there is a stone called marcasite, but the stone is more brittle then pyrite. Marcasite is never used as a gem, unlike pyrite.