CategoryMica group
(repeating unit)

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.[1][2]

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


  1. ^
  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)