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Fe-F avoidance in silicates is a widely accepted concept having a basis in the energetics of reactions (Ramberg 1952) and crystal field theory (Burns 1993). This concept has been extended to suggest the possibility of Mg-Cl and Al-F avoidance in silicates. What about Fe-F avoidance in phosphates? Is anyone aware of reports or discussion of this phenomenon in the literature? My particular interest is the triplite and triploidite group of minerals where ordering of F seems to depend the Fe/(Fe+Mn+Mg) and Mn/(Fe+Mn+Mg) ratios. The Fe end member of the triplite group, zwieselite, Fe2PO4F, appears to violate Fe-F avoidance, yet it has been synthesized and its crystal structure solved. Any suggestions on where to look for papers on this subject would be most appreciated. Ed++++++++++++++++++++++++++++++++++++ Edward S. Grew Department of Geological Sciences University of Maine 5790 Bryand Research Center Orono, Maine 04469-5790 USA Tel: 207-581-2169 Fax: 207-581-2202 E-mail: [log in to unmask] Homepage: http://www.geology.um.maine.edu/user/ed_grew/