BRADACZEKITE, NaCu4(AsO4)3, A NEW MINERAL SPECIES FROM THE TOLBACHIK VOLCANO, KAMCHATKA PENINSULA, RUSSIA

Bradaczekite, NaCu4(AsO4)3, was discovered in a fumarole in the North Breach of the Great fissure Tolbachik eruption (GFTE) in 1975–1976, Kamchatka Peninsula, Russia. Bradaczekite forms aggregates of dark blue plates elongate along [¯102]. The well-developed forms are {010}, {¯311}, {111} and {¯112}. The forms {¯301}, {001}, {¯321}, {¯101}, {100}, {021}, {110}, {¯131}, {¯111} and {341} are common. Associated minerals are hematite, tenorite, lammerite, urusovite, orthoclase and johillerite. The mineral has an adamantine luster and a light blue to white streak. No cleavage has been observed. The mineral is transparent, biaxial, optically negative, 1.76(1), 1.92(1), 1.96(1), 2Vcalc 50.0°. The optical orientation is Z = b, X c = 23 ° in the obtuse angle. Bradaczekite shows strong pleochroism: X violet-red, Y green, Z greenish blue. The mineral is monoclinic, space group C2/c, a 12.051(1), b 12.434(1), c 7.2662(7) Å, 117.942(1)°, V 961.8(2) Å3, Z = 4, Dcalc = 4.77(1) g/cm3 (for the empirica