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

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  • Università di Pisa
  • Museo di Storia Naturale dell’Università di Pisa
  • Istituto di Geologia Ambientale e Geoingegneria

Abstract

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.

Details

Original languageEnglish
Number of pages18
JournalMinerals
Volume12.2022
Issue number51
DOIs
Publication statusE-pub ahead of print - 30 Dec 2021