Nanoporous materials are solid materials showing channels, pores or cavities with at least one dimension in the nanometer range. The most common and prototypical nanoporous materials are represented by the zeolites. Zeolites are crystalline solids with well-defined structures that generally contain silicon, aluminium and oxygen in their framework and cations, water and/or other molecules within their pores. Many occur naturally as minerals, and are extensively mined in many parts of the world. Others are synthetic, and are made commercially for specific uses, or produced at research labs on trying to understand more about their chemistry. Because of their unique porous properties, zeolites are used in a variety of applications with a global market of several million tonnes per annum. Major uses are in petrochemical cracking, ion-exchange (water softening and purification), and in the separation and removal of gases and solvents. They are often also referred to as molecular sieves.