Pyrite is a widely spread natural mineral and important organic material. It participates in numerous geochemical processes, including oxidation reactions that cause acid mine drainage. In this book, the authors discuss pyrites synthesis, characterisation and uses. Topics include the use of pyrite as a concentrator of gold in laboratory and natural systems; oxidative degradation of organic pollutants by fenton reaction in pyrite suspension; potentiometric characterisation and analytical application of pyrite mineral for the assay of weak organic acids in non-aqueous media; sorption of mercury(II) to synthesised pyrite (FES2) and stabilisation via surface reaction; the pyritisation of fossils from the cretaceous period of the Langerstatte Araripe Basin, in Northeast Brazil; and pyrite phases as high pressure polymorphs of dioxides and other compounds.