Zoisite-(Pb), a New Orthorhombic Epidote-Related Mineral from the Jakobsberg Mine, Värmland, Sweden, and Its Relationships with Hancockite

The new mineral zoisite-(Pb), ideally CaPbAl ₃ (SiO ₄)(Si ₂ O ₇)O(OH), was discovered in a sample from the Jakobsberg manganese-iron oxide deposit, Värmland, Sweden. Zoisite-(Pb) is found as pale pink subhedral prisms elongated on [010], up to 0.3 mm in size, associated with calcite, celsian, diopside, grossular, hancockite, hyalophane, native lead, phlogopite, and vesuvianite. Associated feldspars show one of the highest PbO contents (~7–8 wt%) found in nature. Electron-microprobe analysis of zoisite-(Pb) point to the empirical formula (Ca _1.09 Pb _0.86 Mn ²⁺ 0.01Na _0.01) _∑1.97 (Al _2.88 Fe ³⁺ 0.10 Mn ³⁺ 0.04) _∑3.02 Si _3.00 O ₁₂ (OH) _1.00 . The eight strongest diffraction lines [d _obs, I _obs, (hkl)] are 8.63 s (101), 8.11 mw (200), 4.895 m (011), 4.210 m (211), 3.660 s (112, 311), 3.097 mw (312), 2.900 s (013), and 2.725 m (511). Zoisite-(Pb) is isostructural with zoisite and its crystal structure was refined up to R ₁ = 0.0213 for 2013 reflections with F _o > 4σ(F _o). Pb shows a stereochemically active lone pair leading to a lopsided distribution of its coordinating oxygens. A full chemical and Raman characterization of zoisite-(Pb) and of the Pb-bearing epidote hancockite is reported, together with an improved crystal structural model of hancockite, refined up to R ₁ = 0.0254 for 2041 reflections with F _o > 4σ(F _o). The effects of the incorporation of Pb in the crystal structure of zoisite-(Pb), hancockite, and related synthetic and natural phases are described and discussed.