Amazonite, also known as Amazonstone, is a green tectosilicate mineral, a variety of the potassium feldspar called microcline. Its chemical formula is KAlSi3O8, which is polymorphic to orthoclase. Its name is taken from that of the Amazon River, from which green stones were formerly obtained, though it is unknown whether those stones were amazonite. Although it has been used for over two thousand years, as attested by archaeological finds in Egypt and Mesopotamia, no ancient or medieval authority mentions it. It was first described as a distinct mineral only in the 18th century. Green and greenish-blue varieties of potassium feldspars that are predominantly triclinic are designated as amazonite. It has been described as a "beautiful crystallized variety of a bright verdigris-green" and as possessing a "lively green colour." It is occasionally cut and used as a gemstone. Occurrence Amazonite is a mineral of limited occurrence. Formerly it was obtained almost exclusively from the area of Miass in the Ilmensky Mountains, 50 miles southwest of Chelyabinsk, Russia, where it occurs in granitic rocks. Amazonite is now known to occur in various places around the globe. Those places are, among others, as follows: China: Baishitouquan granite intrusion, Hami Prefecture, Xinjiang: found in granite Libya: Jabal Eghei, Tibesti Mountains: found in granitic rocks Mongolia: Avdar Massif, Töv Province: found in alkali granite South Africa: Mogalakwena, Limpopo Province Khâi-Ma, Northern Cape Kakamas, Northern Cape Ceres Valley, Western Cape Sweden: Skuleboda mine, Västra Götaland County: found in pegmatite United States: Colorado: Deer Trail, Arapahoe County:233 Custer County:234 Devils Head, Douglas County:234 Pine Creek, Douglas County:234 Crystal Park, El Paso County:234 Pikes Peak, El Paso County: found in coarse granites or pegmatite St. Peter's Dome, El Paso County:234 Tarryall Mountains, Park County:235 Crystal Peak, Teller County:235 Virginia: Morefield Mine, Amelia County: found in pegmatite Rutherford Mine, Amelia County Pennsylvania: Media, Delaware County:244 Middletown, Delaware County:244 Color For many years, the source of amazonite's color was a mystery. Some people assumed the color was due to copper because copper compounds often have blue and green colors. A 1985 study suggests that the blue-green color results from quantities of lead and water in the feldspar. Subsequent 1998 theoretical studies by A. Julg expand on the potential role of aliovalent lead in the color of microcline. Other studies suggest the colors are associated with the increasing content of lead, rubidium, and thallium ranging in amounts between 0.00X and 0.0X