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First high-pressure synthesis of rossmanitic tourmaline and evidence for the incorporation of Li at the X site

Authors
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Kutzschbach,  Martin
4.3 Chemistry and Physics of Earth Materials, 4.0 Geomaterials, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

/persons/resource/wunder

Wunder,  B.
4.3 Chemistry and Physics of Earth Materials, 4.0 Geomaterials, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

/persons/resource/marija

Krstulovic,  Marija
4.3 Chemistry and Physics of Earth Materials, 4.0 Geomaterials, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

Ertl,  Andreas
External Organizations (TEMPORARY!);

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Trumbull,  R.
3.1 Inorganic and Isotope Geochemistry, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

/persons/resource/rocholl

Rocholl,  A.
3.1 Inorganic and Isotope Geochemistry, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

Giester,  Gerald
External Organizations (TEMPORARY!);

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Citation

Kutzschbach, M., Wunder, B., Krstulovic, M., Ertl, A., Trumbull, R., Rocholl, A., Giester, G. (2017): First high-pressure synthesis of rossmanitic tourmaline and evidence for the incorporation of Li at the X site. - Physics and Chemistry of Minerals, 44, 5, 353-363.
https://doi.org/10.1007/s00269-016-0863-0


Cite as: https://gfzpublic.gfz-potsdam.de/pubman/item/item_1860897
Abstract
Lithium is an important component of some tourmalines, especially in chemically evolved granites and pegmatites. All attempts at synthesizing Li-rich tourmaline have so far been unsuccessful. Here we describe the first synthesis of rossmanitic tourmaline at 4 GPa and 700°C in the system Li2O-Al2O3-SiO2-B2O3-H2O (LASBH) from seed-free solid starting materials consisting of a homogenous mixture of Li2O, γ-Al2O3, quartz, and H3BO3. The solid run products after 12 days run duration comprise rossmanitic tourmaline (68 wt.%), dumortierite (28 wt.%) and traces of spodumene (3 wt.%) and coesite (1 wt.%). Tourmaline forms idiomorphic, large prismatic crystals (30 × 100 μm), which are inclusion-free and chemically unzoned. The refined cell-dimensions of the tourmaline are: a = 15.7396(9) Å, c = 7.0575(5) Å, V = 1514.1(2) Å3. Conventionally, the Li+ ion is assumed to exclusively occupy the octahedral Y site in the tourmaline structure to a maximum of 2 Li per formula unit (pfu). However, the chemical composition of our synthetic tourmaline determined by electron microprobe and secondary ion mass spectroscopy results in the formula: X(☐0.67(11)Li0.33(11))Y(Al2.53(10)Li0.47(10))Z(Al6)T(Si5.42(15)B0.58(15))O18 B(BO3)3V+W[(OH)2.40(3)O1.60(3)], wherein a significant amount of Li occupies the X site for charge balance requirements. Reliable assignment of the OH-stretching vibrations in a polarized single-crystal Raman spectrum such as a single-crystal XRD structure refinement, confirm the incorporation of Li at the X site [0.24(9) and 0.15(5) XLi pfu, respectively]. The SREF-data show that the Li-O1 distances are shortened significantly in order to compensate for the smaller ionic radius of Li+ compared to Na+, K+ or Ca2+ at the X site, i.e. Li is closer to the Si6O18 ring and to a 7-fold coordination with oxygen.