3.2" Pyrite Sun - Sparta, Illinois
People used to believe that pyrite suns were fossils which had undergone pyrite replacement. The current consensus is that they are simply formed due to the enormous pressure compacting the slate, and causing pyrite to grow laterally in a radiating manner.
FeS2, otherwise known as Pyrite, or 'Fool's Gold' contains about 47 percent iron and 53 percent sulfur. It gets the name 'fool's gold' because of its brassy golden color, however; the name pyrite comes from the Greek word pur meaning "fire." In ancient times pyrite was struck against flint to create sparks and start fires.