Coparsite, Cu4O2[(As,V)O-4]Cl, a new mineral species from the Tolbachik volcano, Kamchatka Peninsula, Russia

Coparsite, ideally Cu4O2[(As,V)O-4]Cl, occurs in the fumarole "Yadovitaya" (= "Poisonous") in the North Breach of the great fissure Tolbachik eruption (1975-1976), Kamchatka Peninsula, Russia. It occurs as black or dark grey crystals, tabular on (100), elongate in the [010] direction, with well-deve loped {100}, {110} and {101} forms. Associated minerals are euchlorine, tol bachite, kamchatkite, ponomarevite, minerals from the klyuchevskite-alumokl yuchevskite solid-solution series, hematite, tenorite and vanadian lammerit e. The grains of coparsite are found as small black inclusions in emerald-g reen euchlorine. The mineral has a metallic luster and a brown streak. Non- fluorescent. It is very brittle and thus does not allow measurements of har dness. Cleavage is perfect on the (100) plane. Coparsite is orthorhombic, s pace group Pbcm, a 5.440(1), b 11.154(2), c 10.333(2) Angstrom, V 627.0(3) Angstrom(3), Z = 4, D-calc = 4.76(1) g/cm(3) (based on the empirical formul a). Diagnostic lines of the X-ray powder-diffraction pattern [d in Angstrom (I)(hkl)] are: 5.31(30)(010), 4.69(40)(110), 3.70(30)(012), 3.03(60)(310), 2.82(10)(113), 2.62(100)(312), 2.39(40)(022,221), 1.67(20)(324,405). Electr on-microprobe analyses yielded: CuO 69.03 (67.68-70.16), Fe2O3 0.17 (0-0.87 ), As2O5 15.50 (13.13-20.23), V2O5 7.72 (4.06-9.24), SO3 0.57 (0.20-0.99), Cl 8.47 (8.17-8.75), subtotal 101.46, O = Cl-2-1.91 (1.84-1.97), total 99.5 5 (98.09-101.55) wt%. The empirical formula, normalized to O + Cl = 7 apfu, is Cu3.89Fe0.01O1.93 [(As0.60V0.38S0.03)O-4]Cl-1.07, close to the ideal Cu 4O2((As,V)O-4)Cl confirmed by crystal-structure analysis. The mineral is na med after its chemical composition: cop(per) + ars(enic).