This book has been divided into three sections. The first section contains one chapter setting out the geological origins of sedimentary pyrite. Section two contains five chapters that provide detailed insights into the behavior of reactive pyrite and pyrrhotite when present in construction aggregates. Most recently, the consequences for property owners in Québec, Ireland and Connecticut, from iron sulfides in unbound aggregates and in aggregates in concrete have been devastating both financially and emotionally to building owners. When, through no fault of their own, their house loses some or all of its value, the impact on homeowners’ lives can be shattering. The third section deals with the more positive aspects of pyrite and how emerging research is showing its value as a low-cost material for such diverse applications as coatings for solar panels and as a growth enhancer for agricultural crops.