Microcline, potassium aluminum silicate, is a member of a large group of minerals known as feldspars. Feldspars are perhaps the most common and abundant minerals on earth and occur in nearly all igneous and metamorphic rocks. Microcline has a triclinic structure, versus the more common orthoclase, a potassium feldspar with a monoclinic structure. Microcline is usually colorless and forms excellent crystals, such as the ones from Florissant and other localities in Colorado. A green form of microcline, called amazonite, is a popular gem material.