Manganobadalovite, NaNaMn(MgFe3+)(AsO4)3, a New Alluaudite-Group Mineral from the Tolbachik Volcano, Kamchatka, Russia

The new alluaudite-group mineral manganobadalovite (IMA 2020-035), ideally NaNaMn(MgFe3+)(AsO4)3, was found in the Arsenatnaya fumarole, the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption 1975–1976, Tolbachik volcano, Kamchatka peninsula, Far-Eastern Region, Russia. Manganobadalovite is a fumarolic mineral, and its aggregates are found overgrowing basalt scoria or exhalative hematite crystal crusts. Associated minerals are badalovite, hematite, cassiterite, sanidine, glauberite and metathénardite. Manganobadalovite occurs as prismatic to equant crystals up to 0.8 mm long typically combined in open-work clusters; it also forms grains that are irregular in shape and cavernous granular crusts up to 0.5 cm. The mineral is transparent, with vitreous luster, and its color varies from red to yellow. Manganobadalovite is brittle and has a noticeable cleavage in one direction and uneven fracture. The calculated density is 4.108 g cm−3. Manganobadalovite is optically biaxial (+), α = 1.790 (7), β = 1.800 (7), γ = 1.815 (8) and 2Vmeas = 80 (5)°. Chemical composition (wt.%, electron-microprobe): Na2O 8.75, K2O 0.17, MgO 5.32, CaO 3.68, MnO 10.09, CuO 0.42, Al2O3 0.18, Fe2O3 13.90, V2O5 0.42, As2O5 56.75, total 99.68. The empirical formula calculated based on 12 O apfu is Na1.69K0.02Ca0.39Mn0.85Mg0.79Cu0.03Fe3+1.04Al0.02(As2.96V0.03)∑2.99O12. The crystal structure was solved using single-crystal XRD data, R = 2.30%. Manganobadalovite is monoclinic, C2/c, a = 12.1848(5), b = 12.8924(4), c = 6.6970(3) Å, β = 113.113(5)°, V = 967.60(7) Å3 and Z = 4. The strongest reflections of the powder XRD pattern are d,Å(I)(hkl): 6.43(30)020, 3.589(32)(−131, 310), 3.215(38)(040, −112), 3.079(23)(221, 002), 2.941(32)(−312, −222, −331), 2.852(15)(041), 2.788(100)(330, 400, 240, 022), 2.649(22)(−402, 112), 2.626(25)(−132). Manganobadalovite is named as an analogue of badalovite NaNaMg(MgFe3+)(AsO4)3 with Mn2+ prevailing in the M(1) site.