Phengite

Phengite
General
Category	Phyllosilicate minerals
Group	Mica group, dioctahedral mica group
Variety of	Muscovite
Formula	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]

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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