栃木県鹿沼市板荷産含バナジン満礬石榴石

概要

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A grey yellow spessartine of contact metamorphic origin from Itaga, Kanuma City, Tochigi Prefecture, contains 0.21 to 0.87 wt.% of V_2O_3,yielding the empirical formula (Mn_<2.63>Ca_<0.29>Fe^<2+>_<0.07>_<Σ2.99>(Al_<1.85>Fe^<3+>_<0.08>V^<3+>_<0.06>)_<Σ1.99>(Si_<2.98>Ti_<0.03>)_<Σ3.01>O_<12.00> for the most vanadium-rich point. The grain analysed is discontinuously rimmed with a spessartine-grossular solid solution with the formula (Mn_<1.56>Ca_<1.48>)_<Σ3.04>(Al_<1.91>Fe^<3+>_<0.03>V^<3+>_<0.02>)_<Σ1.96>(Si_<2.94>Fe^<3+>_<0.05>Ti_<0.01>)_<Σ3.00>O_<11.96>. The material represents an example of concentration of vanadium in a manganese silicate ore without forming any independent mineral of vanadium, which was concentrated therein prior to the metamorphism. The garnet occurs as isolated trapezohedra in an aggregate of blady rhodonite, which involves an aggregate of siegenite and cobaltite, the former proving a lower concentration of arsenic.
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