A detailed investigation was conducted on high-pressure (~1.4 GPa) tourmaline from an Eoalpine mafic eclogite, which occurs in the Kreuzeck Mountains, Eastern Alps, Austria. Tourmaline from this locality contains the highest amount of Sr2+ (up to 0.68 wt% SrO) known to date. The space group is R3m with unit-cell parameters a = 15.944(1), c = 7.202(1) Å, V = 1585.5(3) Å3. Analyses by a combination of electron microprobe, optical absorption spectroscopy and crystal-structure refinement (R1 = 1.31%) result in the structural formula X(Na0.85Ca0.08Sr0.06K0.01)Σ1.00Y(Mg1.68Al0.70Fe0.373+Ti0.104+Fe0.112+Ca0.03Cr0.013+)Σ3.00Z(Al5.15Mg0.80Fe0.053+)Σ6.00T(Si5.82B0.10Al0.08O18) (BO3)3V(OH)3W[O0.45(OH)0.35F0.20]. The T site contains mainly Si and additionally small amounts of B and Al. According to optical absorption spectroscopy (using the band near 1120 nm), the Fe3+/Fe ratio is 79 ± 2%, suggesting that this high-pressure tourmaline crystallized under oxidizing conditions. It has a significant oxy-dravite component. A near-rim zone contains 0.6 wt% Cr2O3, 0.5 wt% PbO2, 0.2 wt% NiO and 0.1 wt% V2O3. Only a small F content was found by structure refinement. There is no evidence for significant X-site vacancy in the investigated tourmaline zones. We assume that the original boron source for tourmaline crystallization in the eclogite, i.e. tourmaline-bearing pegmatites in the country-rock, were influenced by a Sr-bearing marble.

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