Phengite

Originally named in 1841 by Johann Friedrich August Breithaupt as a group of micas showing biaxial characteristics, and applied as a genus name to all of the known biaxial mica minerals then defined. The origin of the name in German is from "feurig" suggesting glowing or fiery, presumably due to the mineral's luster and that property was translated to the Greek φλογερός, also meaning fiery. In 1853, Franz von Kobell discarded phengite as a genus name, partly because binomial nomenclature of minerals had been discarded, and he resurrected the name phengite and defined it as a muscovite with high silica contents, as a way of discussing mica formulas with varying fixed molecular forms. However, James D. Dana criticized the use of phengite in 1854 and von Kobell apparently abandoned the name. Alexander N. Winchell (1925) resurrected phengite in the same manner used by von Kobell in order to assign fixed molecular mixing to account for excess Si substitution in muscovite. Guidotti (1984) and others called slightly hypersilicic muscovite "phengitic muscovite" or simply phengite when Si was greater than 3.5 pfu. In 1998, phengite was defined as a high silica variety of muscovite on the chemical join between muscovite, celadonite, and aluminoceladonite, depending on the composition of the octahedral substitutions, but phengite ceased to be considered an end-member composition.