The crystal chemistry of viridines and kanonaite, (Al t FeJ + ) 2 (0|Si0 4 ), has been evaluated with special reference to the behavior of Mn 3+ in this andalusite type structure. Five natural samples (from Ultevis: Χ = 0.012, . Y = 0.028; from Yakutia: JC = 0.076, y = 0.046; from Tanzania: χ = 0.091, y = 0.031; from Darmstadt: Λ; = 0.171, y = 0.048; from Kanona: Χ = 0.340, y = 0.009) and two synthetic viridines (PI35: χ = 0.173, y = 0.005; Ρ150: χ = 0.22, y = 0) have been studied by means of X-ray powder diffraction, single crystal-structure refinements, 57 Fe y-resonance spectroscopy, and optical absorption microspectroscopy.The structure refinements reveal that the transition metal ions substitute for Al almost exclusively in the distorted octahedral Al(l) site of the andalusite structure type within the entire mixed crystal series. This is independently proven by the Mössbauer results for 57 Fe, which show that only 10 to 15 % of total iron is present in the Al(2) trigonal-bipyramidal site. With increasing substitution, the octahedral (c/a)«., ratio increases. This