Complete solid solution between magnesian schorl and lithian excess-boron olenite in a pegmatite from the Koralpe (eastern Alps, Austria)

At the margins of a plagioclase-quartz pegmatite near Stoffhutte (Koralpe, Austroalpine realm, Austrian Alps), a new solid solution series within the tourmaline group (XY(3)Z(6)[T6O18](BO3)(3)V3W) has been found, namely betwe en magnesian schorl and lithian excess-boron olenite. At the pegmatite cont act with mylonitic garnet-biotite schists, a tourmalinite band developed. M assive tourmaline cores are Mg-rich schorl with normal boron contents of 3. 0 cations per formula unit that most likely formed by a reaction of melt wi th garnet. Within the pegmatite, only olenitic crystals were found. Within a transition zone, the Mg-rich schorl crystals become zoned and develop ole nitic rims of increasing size, most likely formed from a fluid via the reac tion plagioclase + H2O + B2O3 = olenite + quartz,,As values as well as incr easing B, Al The major compositional changes are decreasing Fe, Mg and Si c ontents and X-Mg and Li contents. Over a distance of less than five centime tres, tourmaline composition determined by secondary ion microprobe (B, Li, Be, H) and electron microprobe (remaining elements, total Fe as Fe2+) vari es continuously from (Na0.90Ca0.11)(Fe(1.61)Mg(1.10)Mn(0.01)Ti(0.11)Zn(0.01 )Li(0.01)Al(0.10)square (0.05))Al-6.00[Si6.01O18](B2.99O9)(OH3.02F0.23O0.75 ) to (Na(0.42)Ca(0.31)square (0.27))(Fe0.14Mg0.03Mn0.01Ti0.06Li0.33Be0.01Al 2.49)Al-6[Si4.91Al0.21B0.88O18](B3.00O9)(OH3.38F0.07). In contrast to the p roton-deficient ideal olenite, the olenitic tourmaline from Stoffhutte cont ains 3.0-3.4 hydrogens per formula. The main substitutions are most likely Al-[Y](3+) + B-[T](3+) = [T]Si4+ + ([Y])(Mg, Fe)(2+), which is a modified T schermaks' substitution, ([Y])A(3+) + Li-[Y](+) = 2 ([Y])(Mg, Fe)(2+), Ca-[ X](2+) + ([X])square = 2 Na-[X](+), Al-[Y](3+) + ([X])square = Na-[X](+) ([Y])(Mg, Fe)(2+) and Fe-[Y](2+) = Mg-[Y](2+). Coexisting muscovite and fel dspar have considerable B (0.42-0.55 wt% and 71-134 ppm, respectively), Be (49-140 ppm and 79-169 ppm, respectively) and Li contents (6-9 ppm and 9-12 6 ppm respectively), The apparent partition coefficient for total B between tourmaline and muscovite (D-B = c(tur)/c(ms)) varies between 6.5 and 16.8, but the values for tetrahedrally coordinated B (D-B(T)) range from 0 to 13 .0.