Joelbruggerite, Pb3Zn3(Sb5+,Te6+)As2O13(OH,O), the Sb5+ analog of dugganite, from the Black Pine mine, Montana

Abstract

Joëlbruggerite, ideally Pb3Zn3(Sb5+,Te6+)As2O13(OH,O), is a new arsenate mineral (IMA 2008-034) and the Sb5+ analog of dugganite, from the Black Pine mine, 14.5 km northwest of Philipsburg, Granite County, Montana. It is usually found perched on mimetite; other species that may be present include malachite, azurite, pseudomalachite, chalcocite, beudantite-corkite, duftite, dugganite, and kuksite, in milky quartz veins. Joëlbruggerite occurs as barrel-shaped or prismatic crystals up to about 50 μm across in various shades of purple. The crystals have an adamantine luster and a white streak. Mohs hardness is about 3. The fracture is irregular, and the tenacity is brittle. Joëlbruggerite crystals are uniaxial (-), with a calculated refractive index of n = 1.993, and weakly pleochroic: X = Y = gray, Z = purple; absorption: Z > X = Y. Crystals show straight extinction and are length-fast. The empirical chemical formula (mean of 5 electron microprobe analyses) calculated on the basis of 14 [O + OH] anions is Pb3.112(Zn2.689Fe2+0.185)Σ2.874(Sb5+0.650Te6+0.451)Σ1.101(As1.551P0.203Si0.160)Σ1.914O13.335(OH)0.665. Joëlbruggerite is trigonal, space group P321, a = 8.4803(17), c = 5.2334(12) Å, V = 325.94(12) Å3, Z = 1. The five strongest lines in the powder X-ray diffraction pattern are [dobs in Å (I) (hkl)]: 3.298 (100) (111), 3.008 (89) (021), 1.905 (39) (122, 131), 2.456 (36) (012, 121, 030), and 1.609 (30) (112, 132, 231, 140). The crystal structure was solved from single-crystal X-ray diffraction data and refined to R1 = 0.038 on the basis of 604 unique reflections with F > 4σ(F). It is composed of heteropolyhedral sheets of edge-sharing (Sb,Te)O6 octahedra and PbO8 disphenoids, oriented parallel to (001). The sheets are cross-linked by AsO4 and ZnO4 tetrahedra, which share corners to form an interlinked, two- and threeconnected two-dimensional net parallel to (001). The mineral is named for Joël Brugger (born 1967), Swiss-Australian mineralogist, for his contributions to mineralogy.