Fluor-rossmanite, ideally □(Al2Li)Al6(Si6O18)(BO3)3(OH)3F, is a new mineral of the tourmaline supergroup, found at the Krutaya pegmatite, Malkhan pegmatite field, Zabaykalskiy Krai, Western Siberia, Russia. It forms an intermediate zone up to 3 mm thick in a chemically heterogeneous, concentrically zoned, polychrome tourmaline crystal 3 x 2 cm in size. The new mineral is light pink, transparent with a white streak and a vitreous lustre. It is brittle, with conchoidal fracture. Mohs' hardness is 7. The Dmeas = 3.07(2) g cm-3 and Dcalc = 3.071 g cm-3. Optically, fluor-rossmanite is non-pleochroic, uniaxial (-), ω = 1.647(2), ε = 1.628(2) (589 nm). The empirical formula calculated on the basis of 31 anions (O+OH+F) is: X (□0.46Na0.32Ca0.20Pb0.02)Σ1.00 Y (Al1.84Li1.05Mn0.05Fe 2+ 0.02Ti0.02Cr0.01)Σ2.99 Z Al6.00 T (Si5.79Al0.21)Σ6.00 B2.99O27 V (OH)3 W [F0.44(OH)0.20O0.36]Σ1.00. Fluor-rossmanite is trigonal, R3m; the unit-cell parameters are: a = 15.7951(3), c = 7.08646(17) Å, V = 1531.11(7) Å 3 , and Z = 3. The crystal https://doi.org/10.1180/mgm.2024.34 Published online by Cambridge University Press 2 structure is refined from single-crystal X-ray diffraction data [R = 0.0211 for 1178 unique reflections with I > 2s(I)]. The new mineral is a "fluor-" species belonging to the X-vacant group of the tourmaline supergroup. The closest end-member compositions of valid tourmaline species are those of rossmanite and fluor-elbaite, to which fluor-rossmanite is related by the substitutions W F-↔ W OH-and X 2□ + Y Al 3+ ↔ X 2Na + + Y Li + , respectively.