Phengite

Phengite is a series name for dioctahedral micas of composition K(AlMg)2(OH)2(SiAl)4O10 it is common for Mg or Fe2+ to substitute for Al on the Y site and a corresponding increase in Si on the Z site in the mica group formula X2Y4–6Z8O20(OH, F)4. Similar to muscovite but with addition of magnesium. It is a non-IMA recognized mineral name representing the series between muscovite and celadonite.[1][2]

Not to be confused with Fengite.
Phengite
General
CategoryMica group
Formula
(repeating unit)		K(AlMg)2(OH)2(SiAl)4O10

The silica content of phengite has been proposed as a geobarometer for the metamorphism of low grade schists.[3]

References
  1. Mindat.org
  2. Mineralienatlas: Phengit
  3. M. E. Fleet and R. A. Howie, Rock-Forming Minerals, Vol. 3A: Micas, Geological Society of London; 2nd ed, 2006, p. 132, ISBN 1-86239-142-4 (accessed through Google books)
  • Glossary of Geology, Fifth Edition, Eds. K.K.E. Neiendorf, J.P. Mehl, J.A. Jackson, American Geological Institute, 2005
  • von Kobell, Franz (1853) Tafeln zur Bestimmung des Mineralien, 5th edition, Munchen.
  • Guidotti, Charles V. (1984) Micas in metamorphic Rocks, reviews in Mineralogy, 13: 357-467.
  • Rieder et al. (1998): Nomenclature of the micas. Canadian Mineralogist 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.
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