Phengite

Phengite
Phengite
General
Category	Mica group
Formula; (repeating unit)	K(AlMg)2(OH)2(SiAl)4O10

Phengite is a series name for dioctahedral micas of composition K(Al,Mg)₂(OH)₂(Si,Al)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 X₂Y_4–6Z₈O₂₀(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]

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

References

^ Mindat.org
^ Mineralienatlas: Phengit
^ 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.