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Mariposa Co., California, USA
© Charles Creekmur
|Name:||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 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.|
Phengite is an aluminous true mica which contains high silica that is tetrahedrally co-ordinated. As tetrahedral Si increases, additional octahedrally co-ordinated cations are necessary for charge balance. This is an uncommon condition as there is normally a composition gap between dioctahedral and trioctahedral micas. The substitutions are not restricted to trivalent(Fe, Al) or divalent cations (Mg, Fe, Mn, etc.), and a mixture of substituents is possible. Guidotti (1984) reviewed the conditions under which Ti4+ might substitute for octahedral Al.
Rieder et al. (1998) noted: "Potassic dioctahedral micas are between, or close to, the joins muscovite-aluminoceladonite and muscovite-celadonite."
Also defined as:
"(1) white micas with Si in excess of 3 apfu (atoms per formula unit) in the tetrahedral T site, thus lying on the joins muscovite-aluminoceladonite, and muscovite-celadonite.
(2) white micas with fairly large amounts of Mg and Fe (whatever its oxidation state) and other scarce heavy cations such as Ti, Cr, etc. in the octahedral M site, the name thus meaning any mica with variable amounts of octahedral Al substituted mostly by Mg and Few, irrespective of whether it is tetrasilicic or not, but implicitly assuming charge balance." (Cibin et al., 2008).
Classification of Phengite
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Relationship of Phengite to other Species
|Member of:||Mica Group|
|Other Members of Group:|
Other Names for Phengite
|Health Warning:||No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.|
References for Phengite
von Kobell, Franz (1853) Tafeln zur Bestimmung des Mineralien, 5th edition, Munchen.
Winchell, Alexander N. (1925)
Guidotti, Charles V. (1984) Micas in metamorphic Rocks, reviews in Mineralogy, 13: 357-467.
Rieder et al., "Nomenclature of the micas", Canadian Mineralogist (1998): 36: 905-912.
Mookherjee, M., and Redfern, S.A.T. (2002) A high-pressure Fourier-transform infrared study of the interlayer and Si-O stretching region in phengite-2M 1. Clay Minerals: 37: 323-336.
Cibin, G., G. Cinque, A. Marcelli, A. Mottana, & R. Sassi (2008): The octahedral sheet of metamorphic 2M1-phengites: a combined EMPA and AXANES study: American Mineralogist 93, 414-425.
Internet Links for Phengite
Localities for Phengite
The map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.