Rossmanite is a new tourmaline species from near Rožná, western Moravia, Czech Republic. It forms pale pink columnar crystals about 25 mm long and 5 mm thick, elongaten along c with striations parallel to c on the prism faces. It is brittle, H= 7, D meas = 3.00 g/cm 3 , D calc = 3.06 g/cm 3 . In plane-polarized light, it is colorless. Rossmanite is uniaxial negative, to = 1.645(1), e = 1.624(1), trigonal, space group R3m, in the hexagonal setting a = 15.770(2), c = 7.085(1) Å, V = 1525.8(4) Å 3 , Z= 3. The strongest six X-ray diffraction lines in the powder pattern are at d = 3.950 Å with I = 100% for (hkl) = (220); 2.552 Å, 93%, (051); 1.898 Å, 72%, (342); 4.181 Å, 58%, (211); 2.924 Å, 56%, (122); and 3.434 Å, 53%, (012). Analysis by a combination of electron microprobe, SIMS, H-line extraction, and crystal-structure refinement gave SiO 2 38.10 wt%, Al 2 O 3 44.60, Na 2 O 1.43, Li 2 O = 1.13, B 2 O 3 = 10.88, H 2 O = 3.70, F = 0.20, O ≡ F 0.08, sum = 99.96 wt%, Fe, Mg, Ca, Mn, Ti, F, K not detected. The formula unit (31 anions) is x (⃞ 57 Na 0.43 ) Y (Li 0.71 Al 2.17 ) z Al 6 (Si 5.92 O 18 ) (B 2.92 O 9 )(OH) 3.83 F 0 . 10 O 0.07 , with the ideal end-member formula ⃞(LiAl 2 )Al 6 (Si 6 O 18 )(BO 3 ) 3 (OH) 4 ; thus rossmanite can be derived from elbaite [Na(Al 1.5 Li 1.5 )(Si 6 O 18 )(BO 3 ) 3 (OH) 4 ] by the substitution x ⃞ 2 + Y Al → x Na 2 + Y Li, where ⃞ = vacancy. The crystal structure of rossmanite was refined to an R index of 1.7% using 1094 observed (5σ) reflections collected with MoKα X-radiation from a single crystal. The structure refinement confirmed the low occupancy of the X site and the presence of Li at the Y site. There is considerable positional disorder at the O1 and O2 sites induced by the local variations in bond-valence distribution associated with ⃞-Na disorder at X and Li-Al disorder at Y.