View larger image | Much of the world’s phosphorus is locked up in phosphate rocks around the globe. A handful of countries have the richest phosphorus resources; shown here are nations with around a billion metric tons or more of recoverable phosphate rock supply (in metric tons). Political instability in some of these nations fuels concerns about the continued accessibility of supplies. Credit: Source: USGS Mineral Commodity Summaries; Image: Redmal/IstockPhoto, adapted by E. Feliciano