Phengite

Phengite
General
CategoryPhyllosilicate minerals, mica group, muscovite variety
FormulaK(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 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.

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

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