Pyrite decay is arguably the most serious problem that confronts conservators caring for geological collections. It affects the minerals pyrite and marcasite and occurs when the sulphide component oxidizes to form ferrous sulphate and sulphur dioxide. This can result in the total destruction of a specimen, and the acidic decay products can destroy specimen labels and damage storage materials. To prevent the occurrence of pyrite decay more needs to be known about the museum conditions in which it can develop. A project has been undertaken to investigate the rate at which pyrite decay can develop. An experiment was set up to expose pyrite and marcasite to extremes of temperature and humidity, undisturbed for a year, the aim being to try and gain more information and determine the best possible storage conditions for pyritic material.