Ti 4+ and Sn 4+ -bearing tourmalines - pressure control and comparison of synthetic and natural counterparts

Journal of Geosciences

article

Oleg S. Vereshchagin¹  Bernd Wunder²  Ivan A. Baksheev³  Franziska D.H. Wilke²  Natalia S. Vlasenko⁴  Olga V. Frank-Kamenetskaya¹ 

[1] Institute of Earth Sciences, Saint Petersburg State University, Universitetskaya Emb. 7/9;GFZ German Research Centre for Geosciences;Geological Faculty, Lomonosov Moscow State University;Centre for Geo-Environmental Research and Modelling ,(Geomodel), Saint Petersburg State, University

关键词: tourmaline;    pyroxene;    jadeite;    tin;    titanium;    hydrothermal synthesis;   

DOI  :  10.3190/jgeosci.345

学科分类：自动化工程

来源: Ceska Geologicka Spolecnost / Czech Geological Society

【 摘 要 】

Me4+-bearing (Me4+ = Sn, Ti) dravite analogs were synthesized in the system MeO2–MgO–Al2O3–B2O3–SiO2–NaO–H2Oat 700 °C and 4/0.2 GPa in four hydrothermal experiments. Tourmalines form rosette-like aggregates and needle-likecrystals that are chemically homogeneous. Tourmaline crystals obtained in high-pressure runs (4 GPa) are much smaller(up to 0.1×2 μm) and have lower Me4+ (0.27 wt. % SnO2, 0.57 wt. % TiO2) than those from the low-pressure (0.2 GPa)runs (up to 1×5 μm; 1.77 wt. % SnO2, 2.25 wt. % TiO2). Synthetic analogs of rutile, quartz and coesite were obtainedin the system TiO2–MgO–Al2O3–B2O3–SiO2–NaO–H2O, whereas synthetic analogs of cassiterite, tin-rich (up to ~19.55wt. % SnO2) Na-pyroxene, MgSn(BO3)2 (Mg-analogue of tusionite), quartz and coesite were synthesized in the systemSnO2–MgO–Al2O3–B2O3–SiO2–NaO–H2O. We suggest that at a high temperature (≥ 700 ºC), the pressure negativelyaffects the Ti incorporation into the tourmaline structure. In contrast, at relatively low pressures, the Ti incorporation intourmaline structures is governed by the Ti content in the mineral-forming medium. Low-pressure conditions are feasiblefor Sn incorporation in the tourmaline structure. The presence of Ti4+ and Sn4+ cations in structures of the synthesizedtourmalines (probably at octahedrally coordinated sites), is also indicated by changes in the unit-cell parameters.

【 授权许可】

CC BY