Chloromenite, Cu9O2(SeO3)(4)Cl-6, a new mineral from the Tolbachik volcano, Kamchatka, Russia

Chloromenite, ideally Cu9O2(SeO3)(4)Cl-6, was found in a fumarole in the No rth Breakthrough of the Great Fissure Tolbachik eruption (1975-76, Kamchatk a Peninsula, Russia). It occurs as transparent, tobacco-green crystals, tab ular on {(1) over bar 01}, elongated in [111] and [1 (1) over bar 1], rarel y in [010]; well-developed forms are {001}, {101}, {(1) over bar 01}, {110} , {011}, {(3) over bar 12}; forms {(3) over bar 01}, {310} are poorly-devel oped. Associated minerals are melanothallite, an unknown scaly mineral, an unknown Se-containing mineral and weathering products. Chloromenite is plastic and has a perfect cleavage on (101), a strong vitre ous luster and a yellowish-green streak. H = 27 kg/mm(2). The mineral is bi axial, optically negative: alpha = 1.87(1), beta = 1.92(1), gamma = 1.94(1) , 2V(meas) = 66(2)degrees, 2V(calc) = 63 degrees; orientation: Y = beta, Z similar to gamma. Pleochroism is clear in the green tones: alpha - green, b eta - light brownish-green, gamma - black brownish-green. Chloromenite is m onoclinic, space group I2/m, a = 14.11(1), b = 6.274(2), c = 13.00(1) Angst rom, beta = 113.0 degrees (1), V = 1059 (2) Angstrom(3), z = 2, D-x = 4.15( 1) g/cm(3). The diagnostic lines of the X-ray ponder diffraction pattern ar e (I-d-hkl): 63-11.3-101, 21-7.419-101; 17-6.51-200; 83-5.56-011; 100-3.45- 103; 39-3.24-(2) over bar 04; 33-2.71-(5) over bar 03,312; 61-2.49-303,402. The crystal structure was solved by direct methods and refined to R = 0.05 1 (wR = 0.128). There are five copper positions in the chloromenite structu re that correspond to five crystal chemically distinct coordination polyhed ra: Cu(l), Cu(5)- the squares [20 + 2Cl] and [4O], Cu(2), Cu(4)- trigonal b ipyramids [4O + Cl] and [50], respectively, Cu(3) - a flattened tetrahedron [2O + 2Cl]. The structure is based on heteropolyhedral sheets parallel to (101) and composed of the [Cu(2)O4Cl], [Cu(5)O-4] and [Cu(1)O2Cl2] coordina tion polyhedra. The bipyramids [Cu(2)O4Cl] are linked through edges with tw o [Cu(S)O-4] and one [Cu(1)O2Cl2] squares. The sheets are linked together t hrough the [Cu(4)O-5] bipyramides and the [Cu(3)O2Cl2] tetrahedra. Microprobe analysis gave the following chemical composition (wt %): CuO 46. 23 (45.33-46.83), ZnO 5.94 (5.76-6.03), SeO2 34.37 (33.48-35.56), Cl 16.57 (16.30-17.08), O = Cl-2 - 3.74 (3.68-3,85), Sigma 99.36 (98.90-99.69). The empirical formula, calculated from O + Cl = 20, Cu7.71Zn0.97Se4.11O13.80Cl6 .20 is close to the ideal one, Cu9O2 (SeO3)(4)Cl-6, confirmed by the crysta l structure analysis. The name chloromenite is chosen in accord with colour and chemical composition: chi lambda omega rho o zeta - "green" (this also indicates that the mineral contains Cl) and mu eta nu alpha zeta - "moon" (this indicates th;it the mineral contains Se).