Shenganfuite, PbTe4+3O5(OH)Cl3(H2O), a New Lead-Tellurite Mineral from the Moctezuma Mine, Sonora, Mexico

Abstract A new mineral species, shenganfuite, ideally PbTe4+3O5(OH)Cl3(H2O), was discovered from the Moctezuma mine, Moctezuma, Sonora, Mexico. It occurs as aggregates of bladed crystals on a quartz matrix. Associated minerals include tellurite and quartz. Shenganfuite is colorless in transmitted light, transparent with a white streak and greasy luster. It is brittle and has a Mohs hardness of ∼3. Cleavage is perfect on (001). The calculated density is 4.713 g/cm3. Optically, shenganfuite is biaxial (+), with α, β, and γ > 1.9 and 2Vmeas. = 77.1(5)°. Electron microprobe analyses yielded an empirical formula (based on 3 Te apfu) of Pb0.99Te4+3.00O5(OH)Cl2.65(H1.95O1.15), which can be simplified to PbTe4+3O5(OH)Cl3(H2O). The strongest powder X-ray diffraction lines are [dobs in Å (hkl) I]: 5.870 (11¯0) 44, 5.333 (011) 56, 4.300 (110) 27, 3.619 (003) 72, 3.591 (12¯1) 100, 3.364 (21¯1) 85. Shenganfuite is triclinic, with space group P1¯ and unit-cell parameters a = 7.22435(15), b = 7.49754(16), c = 11.1856(2) Å, α = 102.3492(18), β = 93.4081(18), 106.4026(19)°, V = 563.10(2) Å3, and Z = 2. The crystal structure of shenganfuite is characterized by two types of layers, designated A and B, alternating along [001]. Layer A consists of the corner- and edge-sharing Te4+Φ4 (Φ = O or OH) disphenoids and layer B edge-sharing 8-coordinated Pb-polyhedra [PbCl6(OH)(H2O)]. There are three crystallographically distinct Te4+ cations and each has four primary bonds to Φ within 2.4 Å, forming distorted trigonal bipyramid coordinations, with one of the equatorial oxygen atoms replaced by the lone-pair electrons of Te4+. Shenganfuite is the fourth lead-chloride-tellurite mineral documented thus far, after choloalite, eztlite, and telluroperite, and represents a new type of structure with a unique layer of polymerized Te4+O4 polyhedra.