Aragonite is a carbonate mineral and one of the three most common naturally occurring crystal forms of calcium carbonate (CaCO3), the others being calcite and vaterite. It is commonly found in Spain, with some deposits also occurring in France, Slovakia and the United States. Aragonite is formed by biological processes, including precipitation from marine and freshwater environments. It is used in aquaria as a means of replicating reef conditions, and as an agent in the removal of pollutants such as zinc, cobalt and lead from contaminated wastewater. This aragonite specimen, measuring 4 by 3.6 by 3.5 centimetres (1.6 in × 1.4 in × 1.4 in), was mined in Los Molinillos in Cuenca, Spain.Photograph credit: JJ Harrison