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(Mg1.68Al0.70Ca0.03)Σ3.00Z(Al5.15Mg0.80)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.
Sr-bearing high-pressure tourmaline from the Kreuzeck Mountains, Eastern Alps, Austria
- Share Icon Share
- Search Site
Andreas Ertl, Dan Topa, Gerald Giester, George R. Rossman, Ekkehart Tillmanns, Jürgen Konzett; Sr-bearing high-pressure tourmaline from the Kreuzeck Mountains, Eastern Alps, Austria. European Journal of Mineralogy doi: https://doi.org/10.1127/ejm/2019/0031-2863
Download citation file: