Phlogopite polytypes

Most of the trioctahedral tme-mica stmctures are M polytypes and a few are 2Mi, 2M2, and 3T polytypes. In dioctahedral micas, the 2Mi sequence dominates, although 3T and M structures have been found. Brittle mica crystal-structure refinements indicate that the IM polytype is generally trioctahedral whereas the 2Mi polytype is dioctahedral. The 10 structure has been found for the trioctahedral brittle mica, anandite (Giuseppetti and Tadini 1972 Filut et al. 1985) and recently was reported for a phlogopite from Kola Peninsula (Ferraris et al. 2000). The greatest number of the reported structures were refined from single-crystal X-ray diffraction data, with only a few obtained from electron and neutron diffraction experiments. 

In this way, Sunagawa et al (1968) identified polytypes IM, 2Mi, 2M2, 20 and 37 in synthetic fluor-phlogopite, and confirmed the presence of polytypes with longer period, whose stacking sequence was however too complex to be identified only on the basis of the surface morphology. 

Endo Y (1968) Growth Spirals and Polytypism of Fluor-phlogopite. J Mineral Soc Jpn 8, Spec, issue 2 39-41 (in Japanese)... 

Sunagawa 1, Endo J, Daimon N, Tate I (1968) Nucleation, growth and polytypism of fluor-phlogopite from the vapom phase. J Crystal Growth 3,4 751... 

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