Zeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents. Zeolites also crystallize in post-depositional environments over periods ranging from thousands to millions of years in shallow marine basins. Naturally occurring zeolites are rarely pure and are contaminated to varying degrees by other minerals, metals, quartz, or other zeolites. For this reason, naturally occurring zeolites are excluded from many important commercial applications where uniformity and purity are essential. Zeolites have been shown to be useful catalysts in a large variety of reactions, from acid to base and redox catalysis.