Structure refinements on four fluorophlogopite crystals, performed in space group C2/m, converged at R = 0.03–0.04, with cell parameters in the ranges a = 5.323–5.324, b = 9.219–9.222, c = 10.116–10.119 Å, β = 100.1–100.3°. Major substitutions are OH− ↔ F−,M3+-oxy (VIM2++OH− ↔ VIM3++O2−) and Ti-oxy substitution: VIM2++2(OH)− ↔ VITi4++2O2−. The fluorophlogopite from Piano delle Concazze exhibits the shortest c-parameter with respect to other fluorophlogopites found in nature. The short c parameter is essentially due to the absence of the hydroxyl group in favor of F− and especially of O2− and to the thus increased attractive interaction between the interlayer cation and the anion content (F−, O2−) located at the O4 site. A comparison with other natural fluorophlogopites (namely from Biancavilla, Etna and Presidente Olegario, Brazil) show intermediate crystal-chemical features for the Piano delle Concazze fluorophlogopite. Particularly at Etna, differences in the chemical composition of the crystallized fluorophlogopites could be related to the various extent of enrichments by transfer of a gas phase achieved in specific parts of the volcanic plumbing system.