Pseudolyonsite, Cu3(VO4)2, a new mineral species from the Tolbachik volcano, Kamchatka Peninsula, Russia

摘要

Pseudolyonsite, ideally Cu3(VO4)2, is a new mineral from the medium-temperature fumaroles of the New Tolbachik scoria cones, Tolbachik volcano, Kamchatka Peninsula, Russia. It occurs as needles that are 5-20 mm across and up to 0.5 mm in the length, which sometimes produce parallel intergrowths, sprays or openwork clusters up to 2 mm. Associated minerals are: piypite, hematite, magnetite, lyonsite, aphthitalite, palmierite, langbeinite, filatovite, lammerite, vergasovaite, rutile and native gold. Pseudolyonsite is dark red with a brownish tint to black, translucent to opaque, with a reddish-brown streak and adamantine to semi-metallic lustre. The mineral is brittle, but thin long needles are flexible. The fracture is conchoidal, and no cleavage was observed. The calculated density is 4.749 g/cm~3. In reflected light in air the mineral is grey with a weak bluish tint, non-pleochroic, has distinct anisotropy and ubiquitous red to orange internal reflections. The reflectance values (R_1 and R_2, ) in air for the four COM wavelengths are, respectively, 17.05, 19.6 (470 nm); 16.1, 18.15 (546 nm); 15.85, 17.7 (589 nm); and 15.55, 17.4 (650 nm). Four electron probe (EDS) analyses produced the following mean values: V_2O _5 40.37, CuO 48.83, ZnO 7.60, MoO_3 1.89, and SiO _2 0.14, total 98.83 wt, which corresponds, on the basis of 8 O atoms, to (Cu_(2.58)Zn_(0.44))Σ3.02(V _(1.88)Mo_(0.06)Si_(0.02))Σ1.96O_8. The idealised formula is Cu_3(VO_4)_2. Pseudolyonsite is monoclinic: P2_1/c, a = 6.2695(4), b = 8.0195(3), c = 6.3620(3) ?, β = 111.96(1)°, V = 296.66(3) A°~3, Z = 2. The strongest powder X-ray diffraction lines d in A° (I) (hkl) are: 4.70 (60) (110); 3.30 (79) (021, 120); 3.22 (87) (111); 3.18 (34) (-121, -102); 2.894 (74) (200, -211); 2.761 (100) (012); 2.479 (59) (-212, -122); 2.419 (67) (031, 130). The crystal structure was solved from single-crystal data and refined to R = 0.0444. Pseudolyonsite is isostructural with synthetic monoclinic Cu _3(VO_4)_2. The crystal structure of pseudolyonsite contains corrugated octahedral layers formed by the chains of edge-shared, distorted Cu(2)- octahedra running along the c axis and connected to each other by distorted Cu(1)-octahedra. The octahedra of both types contain Cu and subordinate Zn, and they are typically Jahn-Teller-distorted. Adjacent octahedral layers are connected to each other by VO_4 tetrahedra. Pseudolyonsite is dimorphous with triclinic mcbirneyite. The name pseudolyonsite comes from its close visual similarity to another vanadate mineral, lyonsite, Cu_3Fe~(3+)_4(VO_4)_6. Both the mineral and its name have been approved by the IMA CNMNC (IMA No. 2009-062)