Pyrite is an important ore of gold. They are created under the same conditions and often found in the same area. Because gold is so valuable, even pyrite that doesn't contain a great deal of gold can be worthwhile to mine.
Interestingly, pyrite is also known as "fool's gold," even though it is not gold. It is a type of iron disulfide.
Pyrite is also used as jewelry. It is cut into cabochons, which are polished but unfaceted gemstones. It's also made into beads. Unfortunately, pyrite is not the best choice for jewelry because it tarnishes very easily. Some fossils have also been made of pyrite. In some cases, these fossils have a beautiful golden sheen.