Abstract
The new mineral zoisite-(Pb), ideally CaPbAl3(SiO4)(Si2O7)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 (Ca1.09Pb0.86Mn2+0.01Na0.01)∑1.97(Al2.88Fe3+0.10Mn3+0.04)∑3.02Si3.00O12(OH)1.00. The eight strongest diffraction lines [dobs, Iobs, (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 R1 = 0.0213 for 2013 reflections with Fo > 4σ(Fo). 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 R1 = 0.0254 for 2041 reflections with Fo > 4σ(Fo). 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.
Highlights
Zoisite and clinozoisite are mixed anion silicates widespread in nature, in locally rockforming phases in low- to medium-grade metamorphic rocks
Clinozoisite belongs to the epidote supergroup [3], which includes phases with monoclinic symmetry, distributed in the allanite, clinozoisite, and dollaseite groups, together with the mineral åskagenite-(Nd)
We report in the present paper the occurrence of the new mineral zoisite-(Pb), with ideal formula CaPbAl3 (SiO4 )(Si2 O7 )O(OH)
Summary
Zoisite and clinozoisite are mixed anion silicates widespread in nature, in locally rockforming phases in low- to medium-grade metamorphic rocks They are polymorphs, with ideal formula Ca2 Al3 (SiO4 )(Si2 O7 )O(OH), with orthorhombic and monoclinic symmetry for zoisite and clinozoisite, respectively. 19,9 present in epidote minerals both as a trace element [7] and as a major component cockite ([8]) and piemontite-(Pb) [9]. Pb is present new data are compared with literature data for hancockite, together withinthe rela epidote minerals both as a trace element [7] and as a major component in hancockite ([8]). We report a full multi-technique study of coexisting zoisite-(Pb) and hancockite from Jakobsberg, including EPMA, Raman, X-ray
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