Pyrite Decay: cause and effect, prevention and cure

Pyrite (FeS2) is a common mineral found in igneous, sedimentary and metamorphic rocks; it may be present in petrology, mineral and palaeontological collections. Pyrite decay, or pyrite oxidation, has been recorded since the 19th century and various methods have been devised over the years to prevent or ’cure’ it with varying degrees of success. Methods of identifying pyrite decay in collections are discussed along with potential problems this can cause to the specimens and associated labels. Up to date prevention methods are discussed, including microclimates, controlled environments, collections surveys and resin coatings. Modern techniques of ‘curing’ pyrite are discussed in detail, including ammonium gas treatment and Ethanolamine Thioglycollate treatment.