Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original Paper

Jan Cempírek, Stanislav Houzar, Milan Novák, Lee A. Groat, Julie B. Selway, Vladimír Šrein

Crystal structure and compositional evolution of vanadium-rich oxy dravite from graphite quartzite at Bítovánky, Czech Republic

Journal of Geosciences, volume 58 (2013), issue 2, 149 - 162

DOI: http://doi.org/10.3190/jgeosci.139

Two types of V-rich dravitic tourmaline (oxy-dravite to dravite) distinct in their color, morphology, paragenesis and composition from graphite quartzite at Bítovánky near Trebíc, Moldanubicum, Bohemian Massif, were studied by means of electron microprobe and single-crystal X-ray diffraction. Green oxy-dravite (GVD) from graphite quartzite is sporadically zoned with V-enriched rims; brown oxy-dravite to dravite (BVD) from mobilized quartz-rich nests is characterized by such V-enriched rims. The formulae derived from chemical and structure data of the two oxy-dravite varieties are
^X(Na_0.534Ca_0.284 0.164K_0.018) ^Y(Mg_1.461V_0.679Al_0.771Fe_0.042Mn_0.003Ti_0.043) ^Z(Al_5.074V_0.237Mg_0.689) ^T(Si_5.782Al_0.218O₁₈) (BO₃)₃ [(OH)_3.058O_0.75F_0.192]
for GVD and
^X(Na_0.539Ca_0.148 0.297K_0.017) ^Y(Mg_0.992V_0.302Al_1.039Fe_0.582Mn_0.011Ti_0.068Cr_0.007) ^Z(Al_5.339V_0.082Mg_0.578) ^T(Si_5.864Al_0.136O₁₈) (BO₃)₃ [(OH)_3.209O_0.621F_0.171]
for BVD, respectively. Both types of V-rich oxy-dravite feature Al-Mg-V disorder between the Y and Z sites; V and Cr are preferentially located at the Y site. The V-rich oxy-dravite from Bítovánky has unusually high Ca contents and high proportion of vacancy at the X site. High concentrations of V in the GVD and late BVD probably result from hydrothermal dissolution of (Ti,V)-oxides during a high-grade metamorphic overprinting of the host graphite quartzite assemblage.