関東山地三波川変成帯中の三波川産アルデンヌ石

概要

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Ardennite from Sanbagawa, Gumma Prefecture, occurs as a subordinate constituent in piemontite schists from two separate quarries. All the analyses have V> As in mole ratio and those with the highest and lowest V_2O_5 contents in one specimen are : SiO_2 30.04,31.25; Al_2O_3 22.28,22.42; Fe_2O_3 2.00,1.54; MnO 26.33,26.09; CaO 2.03,2.88; MgO 2.94,3.29; V_2O_5 7.30,6.22; As_2O_5 2.08,1.53; totals 95.00%, 95.22%, respectively, the second one being with the highest SiO_2 content to date. Those with the highest and lowest MnO contents in another specimen are : SiO_2 30.63,29.92; Al_2O_3 21.65,21.73; Fe_2O_3 3.07,3.06; MnO 24.40,22.38; CaO 3.81,4.56; MgO 4.34,4.23; V_2O_5 5.42,6.26; As_2O_5 0.64,1.70; totals 93.97%, 93.94%, respectively, the last one being with the lowest MnO and highest CaO contents to date. The calculation basis Si+V+As=6 is the best one to derive the structural formula of ardennite, in which slight deficit and excess of octahedral cations are probable. The unit cell parameters of the former material are : a=5.832,b=18.573,c=8.707 A. A new type of vanadium and arsenic concentration is found in manganiferous metamorphic rocks formed under an oxidizing condition, where they are involved in a single mineral ardennite.
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