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+0.01 Na 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 > 4 σ ( 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 > 4 σ ( 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. hematophanite [18], morelandite [19], lindqvistite [20] tegengrenite [21], and ferri-taramite [22]. Zoisite-(Pb) is associated with calcite, celsian, diopside, grossular, hancockite, hyalophane, native lead, phlogopite, and vesuvianite. Zoisite-(Pb) occurs as pale pink subhedral prisms elongated on [010], up to 0.3 mm in size (Figure 1).


Introduction
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 Ca 2 Al 3 (SiO 4 )(Si 2 O 7 )O(OH), with orthorhombic and monoclinic symmetry for zoisite and clinozoisite, respectively. According to literature studies [1,2], zoisite and clinozoisite can be considered as the iron-poor, high-temperature and the iron-rich, lowtemperature phase, respectively. 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). Despite its close relationships with the epidote supergroup, zoisite, given its orthorhombic symmetry, is not included in the former supergroup [3,4]. We report in the present paper the occurrence of the new mineral zoisite-(Pb), with ideal formula CaPbAl 3 (SiO 4 )(Si 2 O 7 )O(OH). The new mineral and its name were approved by the IMA-CNMMNC (IMA-2021-025). Zoisite-(Pb) is isostructural with zoisite, and its crystal chemical relationships with zoisite and with synthetic Sr and is isostructural with zoisite, and its crystal chemical relationships with zoisite a synthetic Sr and Pb zoisites [5,6] are discussed. Zoisite-(Pb) was discovered in th sberg manganese-iron oxide deposit, Filipstad district, Värmland County, Swede type material is deposited in the mineralogical collection of the Museo di Storia N Università di Pisa, Via Roma 79, Calci (Pisa, Italy), under catalogue number 19,9 present in epidote minerals both as a trace element [7] and as a major component cockite ( [8]) and piemontite-(Pb) [9]. In the present study, we report a full multi-te study of coexisting zoisite-(Pb) and hancockite from Jakobsberg, including EPM man, X-ray single-crystal, and powder diffraction data obtained on the same mater new data are compared with literature data for hancockite, together with the rela dote supergroup minerals piemontite-(Pb) and niigataite.
Back-scattered electron images show a patchy zoning characteristic for both zoisite-(Pb) and associated hancockite ( Figure 2). It is mainly related to different Ca/Pb atomic ratios in both zoisite-(Pb) and h ite ( Figure 3). These two phases can, in addition, be distinguished on the basis Al/(Al + Fetot) atomic ratio, as indicated above and confirmed by micro-Raman s copy (see below). Quantitative chemical analyses of associated phases (celsian, vesuvianite, a sular) were carried out using a Jeol JXA-8200 Superprobe at the Department of E ences at the University of Milano (Milano MI, Italy) with an accelerating voltage o It is mainly related to different Ca/Pb atomic ratios in both zoisite-(Pb) and hancockite ( Figure 3). These two phases can, in addition, be distinguished on the basis of their Al/(Al + Fe tot ) atomic ratio, as indicated above and confirmed by micro-Raman spectroscopy (see below). It is mainly related to different Ca/Pb atomic ratios in both zoisite-(Pb) and h ite ( Figure 3). These two phases can, in addition, be distinguished on the basis Al/(Al + Fetot) atomic ratio, as indicated above and confirmed by micro-Raman s copy (see below). Quantitative chemical analyses of associated phases (celsian, vesuvianite, an sular) were carried out using a Jeol JXA-8200 Superprobe at the Department of E ences at the University of Milano (Milano MI, Italy) with an accelerating voltage o a beam current of 5 nA, and a beam diameter of 1 μm. Counting times of 30 s on t positions and 10 s on the backgrounds were used. The following minerals, pure Quantitative chemical analyses of associated phases (celsian, vesuvianite, and grossular) were carried out using a Jeol JXA-8200 Superprobe at the Department of Earth Sciences at the University of Milano (Milano MI, Italy) with an accelerating voltage of 15 kV, a beam current of 5 nA, and a beam diameter of 1 µm. Counting times of 30 s on the peak positions and 10 s on the backgrounds were used. The following minerals, pure metals, and synthetic compounds served as standards: grossular (Si, Al, Ca), fayalite (Fe), rhodonite (Mn), forsterite (Mg), sanbornite (Ba), celestine (Sr), synthetic PbO (Pb), pure metal (Cu), omphacite (Na), K-feldspar (K), and hornblende H123 (F). Results are reported in Table 2. Celsian shows two distinct compositions, with an almost pure celsian with minor K and Na (celsian 1), and an intermediate composition with hyalophane (celsian 2). Both compositions are Pb-rich with an almost constant Pb content of 0.11-0.12 a.p.f.u. To the best of our knowledge, this is the highest Pb content found in natural celsian and hyalophane. Further structural and crystal chemical studies are currently in progress to better define the nature of such peculiar Pb-bearing feldspars. Vesuvianite shows high contents of Pb and Cu, 0.26 and 0.55 a.p.f.u., respectively. Grossular shows an intermediate composition towards andradite and, as expected, a total lack of Pb. Mineral chemistry of our associated phases is strongly related to those found by [26][27][28] on Långban phases. In the recent definition of the margarosanite group [29], the crystal chemical relationships between the lead silicate margarosanite, ideally PbCa 2 Si 3 O 9 , walstromite (BaCa 2 Si 3 O 9 ), and breyite (CaCa 2 Si 3 O 9 ) are described. The occurrence of the lead silicate walstromite in a skarn rock from Jakobsberg is reported, with a complete single-crystal, EPMA, and Raman study of the mineral. Walstromite from Jakobsberg displays a variable composition, in the range of margarosanite 50 -walstromite 50 to ca. margarosanite 70 -walstromite 30 . Walstromite from Jakobsberg is associated with celsian, phlogopite, andradite, vesuvianite, diopside, and nasonite. In [29] it was noticed that celsian associated to walstromite lacks any Pb content, reported as below the EDS detection limit (≤0.2% PbO), in contrast to the relevant Pb contents found both in celsian from Jakobsberg (present study) and from Långban [27].

Micro-Raman Spectroscopy
Unpolarized micro-Raman spectra of both zoisite-(Pb) and hancockite were obtained on the same grains used for the X-ray powder diffraction analyses, in nearly back-scattered geometry with a Horiba Jobin-Yvon XploRA Plus apparatus, equipped with a motorized x-y stage and an Olympus BX41 microscope with a 50× objective. The 532-nm line of a solid-state laser was used. The minimum lateral and depth resolution was set to a few µm. The system was calibrated using the 520.6 cm −1 Raman band of silicon before each experimental session. Spectra were collected, in the range between 100-4000 cm −1 , through multiple acquisitions (three) with single counting times of 60 s, with the laser power filtered at 50%.
Backscattered radiation was analyzed with a 1200 gr mm −1 grating monochromator. Raman spectra were processed using Fityk [30], subtracting the background and fitting the spectra to theoretical peak shapes using Voigt functions. Experimental precision can be estimated at ± 2 cm −1 . The Raman spectra of zoisite-(Pb) is compared with that of hancockite in Figure 4.
Minerals 2022, 12, x FOR PEER REVIEW content, reported as below the EDS detection limit (≤0.2% PbO), in contrast to the r Pb contents found both in celsian from Jakobsberg (present study) and from Långb

Micro-Raman Spectroscopy
Unpolarized micro-Raman spectra of both zoisite-(Pb) and hancockite were o on the same grains used for the X-ray powder diffraction analyses, in nearly ba tered geometry with a Horiba Jobin-Yvon XploRA Plus apparatus, equipped wit torized x-y stage and an Olympus BX41 microscope with a 50× objective. The 532of a solid-state laser was used. The minimum lateral and depth resolution was set μm. The system was calibrated using the 520.6 cm −1 Raman band of silicon befo experimental session. Spectra were collected, in the range between 100-4000 cm −1 , t multiple acquisitions (three) with single counting times of 60 s, with the laser po tered at 50%.
Backscattered radiation was analyzed with a 1200 gr mm −1 grating monochr Raman spectra were processed using Fityk [30], subtracting the background and the spectra to theoretical peak shapes using Voigt functions. Experimental precis be estimated at ± 2 cm −1 . The Raman spectra of zoisite-(Pb) is compared with that cockite in Figure 4. Following literature studies [31], the region between 200-1200 cm −1 can be into three ranges, a 200-500-cm −1 range including vibrational modes mainly relate O vibrations, a 500-750-cm −1 range, with bands mainly related to Si-O-Si bending and a 750-1100-cm −1 range hosting symmetrical stretching of Si-O bonds from bo and Si2O7 groups. The spectra of the two minerals showed relevant differences, es in the spectral ranges 320-540 cm −1 and 700 and 820 cm −1, in agreement with the o tions reported by [32]. In the 3000-3800-cm −1 region, a relatively broad and stron Following literature studies [31], the region between 200-1200 cm −1 can be divided into three ranges, a 200-500-cm −1 range including vibrational modes mainly related to M-O vibrations, a 500-750-cm −1 range, with bands mainly related to Si-O-Si bending modes, and a 750-1100-cm −1 range hosting symmetrical stretching of Si-O bonds from both SiO 4 and Si 2 O 7 groups. The spectra of the two minerals showed relevant differences, especially in the spectral ranges 320-540 cm −1 and 700 and 820 cm −1, in agreement with the observations reported by [32]. In the 3000-3800-cm −1 region, a relatively broad and strong band was observed in both spectra. A shift towards higher wavenumbers of O-H stretching band was observed in the Raman spectrum of hancockite, in keeping with its higher Fe 3+ content, e.g., [33].

X-ray Crystallography
X-ray powder diffraction data for zoisite-(Pb) were collected using a 114.6-mm Gandolfi camera. Data (in Å, for Cu Kα) are listed in Table 3. Indexing was done based on single-crystal diffraction data action data. Single-crystal X-ray studies of zoisite-(Pb) showed it is orthorhombic, Pnma, a = 16.3978 (6) Å, b = 5.5953 (2) Å, c = 10.1953 (3) Å, V = 935.43 (1) Å 3 , and Z = 4. Intensity data for zoisite-(Pb) were collected using a Bruker Smart Breeze diffractometer equipped with an air-cooled CCD detector, and graphitemonochromatized MoKα radiation. The detector-to-crystal distance was 50 mm. Data were collected using ω and ϕ scan modes, in 0.5 • slices, with an exposure time of 30 s per frame. The data were corrected for absorption, Lorentz, and polarization factors using the software package Apex2 [34]. The crystal structure was refined using Shelxl-2014 [35] starting from the atomic coordinates of zoisite given in [36]. Scattering curves for neutral atoms [37] were used, refining mixed occupancies Ca vs. Pb at A2 site and Al vs. Fe at M12 site. The anisotropic structural model converged to 0.0213 for 2013 reflections with F o > 4σ (F o ). Details of data collection and refinement are given in Table 4. Table 3. X-ray powder diffraction data (d in Å) for zoisite-(Pb). Intensity and d hkl were calculated using the software CrystalDiffract (CrystalMaker Software Ltd. Kidlington, UK) on the basis of the structural model given in Table 5. Only the reflections with I calc > 10 are given, if not observed. The eight strongest reflections are given in bold. Intensities were visually estimated: s = strong; ms = medium-strong; m = medium; mw = medium-weak; w = weak; vw = very weak.  Intensity data for hancockite were collected and reduced with the same settings as zoisite-(Pb). The crystal structure was refined using Shelxl-2014 [35] starting from the atomic coordinates of hancockite given in [38] Mixed occupancies of (Ca + Pb) and (Al + Fe) Minerals 2022, 12, 51 9 of 18 were refined for A2 and M3 sites, respectively. The anisotropic structural model converged to 0.0254 for 2041 reflections with F o > 4σ (F o ). Details of data collection and refinement are given in Table 4.
Fractional atom coordinates, site occupancies, and equivalent isotropic displacement parameters for zoisite-(Pb) refinement are reported in Table 5, selected bond distances are reported in Table 6, and the bond-valence calculations, performed through the VESTA software [39] and the bond valence parameters dataset reported in [40], are given in Table 7. Fractional atom coordinates, site occupancies, and equivalent isotropic displacement parameters for hancockite are reported in Table 8, selected bond distances are reported in Table 9, and in in Table 10 are the bond-valence calculations, performed through the VESTA software [39] and the bond valence parameters dataset reported in [40]. CIF files of zoisite-(Pb) and hancockite are available as supplementary material of this paper.

Chemical Data
The full set of spot analyses performed on zoisite-(Pb) and hancockite crystals are reported in Table S1. The relationships between Ca and larger ionic radius cations such as (Pb 2+ , Sr 2+ , Ba 2+ ), henceforth denoted as A 2+ , together with those between Al and (Fe + Mn) 3+ , henceforth denoted as Me 3+ , are reported in Figure 5a,b, respectively. Both data from present and from literature studies (Sterling Hill, [43]; Jakobsberg, [26]; Nezilovo, [44]) were considered. Calcium and A 2+ are inversely related both in zoisite-(Pb) and hancockite data, with hancockite showing (Figure 5a) a more variable A 2+ content when compared with zoisite-(Pb). This pattern is directly related to the marked chemical zoning clearly visible in the BSE image in Figure 2. As regards the relationships between Al and Me 3+ , in agreement with X-ray maps (Figure 3), both zoisite-(Pb) and hancockite from the present study form two distinct clusters (Figure 5b), with zoisite-(Pb) significantly depleted and hancockite enriched in (Fe + Mn) 3+ . Both zoisite-(Pb) and hancockite datasets from the present study resulted as markedly enriched in Al when compared to hancockite data from literature studies (Figure 5b), which cluster at definitely higher contents of (Fe + Mn) 3+ .

Chemical Data
The full set of spot analyses performed on zoisite-(Pb) and hancockite crystals are reported in Table S1. The relationships between Ca and larger ionic radius cations such as (Pb 2+ , Sr 2+ , Ba 2+ ), henceforth denoted as A 2+ , together with those between Al and (Fe + Mn) 3+ , henceforth denoted as Me 3+ , are reported in Figure 5a,b, respectively. Both data from present and from literature studies (Sterling Hill, [43]; Jakobsberg, [26]; Nezilovo, [44]) were considered. Calcium and A 2+ are inversely related both in zoisite-(Pb) and hancockite data, with hancockite showing (Figure 5a) a more variable A 2+ content when compared with zoisite-(Pb). This pattern is directly related to the marked chemical zoning clearly visible in the BSE image in Figure 2. As regards the relationships between Al and Me 3+ , in agreement with X-ray maps (Figure 3), both zoisite-(Pb) and hancockite from the present study form two distinct clusters (Figure 5b), with zoisite-(Pb) significantly depleted and hancockite enriched in (Fe + Mn) 3+ . Both zoisite-(Pb) and hancockite datasets from the present study resulted as markedly enriched in Al when compared to hancockite data from literature studies (Figure 5b), which cluster at definitely higher contents of (Fe + Mn) 3+ . hancockites. Hancockite data from present study are denoted as brown circles, Sterling Hill [43] as yellow triangles, Jakobsberg [26] as dark green circle, and Nezilovo [44] as light green squares.  [43] as yellow triangles, Jakobsberg [26] as dark green circle, and Nezilovo [44] as light green squares.

Crystal Structure Description of Zoisite-(Pb) and Hancockite
Structural features of zoisite and of the epidote group minerals were investigated in depth by several authors [3,[45][46][47]. Zoisite-(Pb) is isostructural ( Figure 6) with zoisite: regular M12 octahedra form by edge sharing octahedral chains, running along b, with the more distorted M3 octahedra linked on both sides of the chain. The Fe 3+ content in zoisite-(Pb) is, as expected, low (0.14 a.p.f.u.) and it is accommodated in the M3 polyhedron, which is distinctly larger ( Table 6) and more distorted than M12 polyhedron. M12 octahedral chains are connected along c through Si 2 O 7 groups, and in the a direction by SiO 4 groups, forming the two distinct A1 and A2 cavities ( Figure 6). A1 cavity has a smaller volume, usually hosting Ca only, whereas A2 has a bigger size, more apt to host cations with an ionic radius larger than Ca (1.06 Å), such as Sr and Pb, with ionic radii of 1.21 and 1.23 Å, respectively (VII coordination) [48]. ular M12 octahedra form by edge sharing octahedral chains, running along b, with the more distorted M3 octahedra linked on both sides of the chain. The Fe 3+ content in zoisite (Pb) is, as expected, low (0.14 a.p.f.u.) and it is accommodated in the M3 polyhedron, which is distinctly larger ( Table 6) and more distorted than M12 polyhedron. M12 octahedra chains are connected along c through Si2O7 groups, and in the a direction by SiO4 groups forming the two distinct A1 and A2 cavities ( Figure 6). A1 cavity has a smaller volume usually hosting Ca only, whereas A2 has a bigger size, more apt to host cations with an ionic radius larger than Ca (1.06 Å), such as Sr and Pb, with ionic radii of 1.21 and 1.23 Å respectively (VII coordination) [48]. The A1 coordination polyhedron (Figure 7a, Table 6) is a regular one, with an homo geneous spatial distribution of bonds. The presence of dominant Pb 2+ in the A2 coordina tion polyhedron reflects instead a lopsided coordination (Figure 7b, Table 6), with the pol yhedral triangular face formed by O3 and O7 anions quite closer to Pb 2+ compared with the polyhedral face formed by four O2 anions. The coordination of Pb 2+ (Table 6) is com pleted by two very long bonds to O8. The A1 coordination polyhedron (Figure 7a, Table 6) is a regular one, with an homogeneous spatial distribution of bonds. The presence of dominant Pb 2+ in the A2 coordination polyhedron reflects instead a lopsided coordination (Figure 7b, Table 6), with the polyhedral triangular face formed by O3 and O7 anions quite closer to Pb 2+ compared with the polyhedral face formed by four O2 anions. The coordination of Pb 2+ (Table 6) is completed by two very long bonds to O8.
This asymmetrical spatial distribution of anions around Pb 2+ can be attributed to the presence of a stereochemically active lone pair of Pb 2+ , with the 6s 2 inert electron doublet ideally located at the empty apex of a distorted pyramidal coordination hosting Pb 2+ . An alternative approach [49], which could be used to identify the presence of the Pb lone pair effect in crystal structures, provides the use of the Voronoi-Dirichlet polyhedra.
This asymmetrical spatial distribution of anions around Pb 2+ can be attributed to the presence of a stereochemically active lone pair of Pb 2+ , with the 6s 2 inert electron doublet ideally located at the empty apex of a distorted pyramidal coordination hosting Pb 2+ . An alternative approach [49], which could be used to identify the presence of the Pb lone pair effect in crystal structures, provides the use of the Voronoi-Dirichlet polyhedra. In Table 11 the unit cell parameters of zoisite-(Pb) are compared with those of zoisite [36], and with those of the synthetic phases Sr2Al3(SiO4)(Si2O7)O(OH) [5] and Pb2Al3(SiO4)(Si2O7)O(OH) [6]. The substitution of Ca by Pb-Sr initially involved A2 site only, as it can be seen in Table 11 by comparing the A1 and A2 polyhedral volumes in zoisite and zoisite-(Pb). With Pb-Sr contents higher than 1 a.p.f.u., both A1 and A2 polyhedra expand (Table 11). The progressive substitution of Ca by Sr-Pb in these phases caused (Table 11) an expansion of unit cell parameters, with a and c unit cell parameters showing a distinctly more pronounced increase compared with the b axis. Table 11. Comparison between unit cell parameters (Å) and geometrical features of A1 and A2 polyhedra of isostructural zoisite phases: (1) Zoisite [36]; (2) present study; (3) synthetic Sr-zoisite [6]; (4) synthetic Pb-zoisite [5]. As defined above, A 2+ indicates (Pb + Sr + Ba) 2+ a.p.f.u. for each phase.
(1)  In Table 11 the unit cell parameters of zoisite-(Pb) are compared with those of zoisite [36], and with those of the synthetic phases Sr 2 Al 3 (SiO 4 )(Si 2 O 7 )O(OH) [5] and Pb 2 Al 3 (SiO 4 )(Si 2 O 7 ) O(OH) [6]. The substitution of Ca by Pb-Sr initially involved A2 site only, as it can be seen in Table 11 by comparing the A1 and A2 polyhedral volumes in zoisite and zoisite-(Pb). With Pb-Sr contents higher than 1 a.p.f.u., both A1 and A2 polyhedra expand (Table 11). The progressive substitution of Ca by Sr-Pb in these phases caused (Table 11) an expansion of unit cell parameters, with a and c unit cell parameters showing a distinctly more pronounced increase compared with the b axis. Table 11. Comparison between unit cell parameters (Å) and geometrical features of A1 and A2 polyhedra of isostructural zoisite phases: (1) Zoisite [36]; (2) present study; (3) synthetic Sr-zoisite [6]; (4) synthetic Pb-zoisite [5]. As defined above, A 2+ indicates (Pb + Sr + Ba) 2+ a.p.f.u. for each phase.
With the increasing substitution of Ca by A 2+ , O4-O6-O5 angle shows a quite limited change, moving from zoisite to zoisite-(Pb), with a more pronounced decrease when moving to synthetic Sr-zoisite and synthetic Pb-zoisite, in agreement with the expansion of A1 cavity along a axis. The T2-O8-M3 angle gradually increases, in agreement with the expansion of A2 cavity along c. Accordingly, the O2-O8 distance, involving two atoms placed on opposite sides of A2 cavity (Figure 8), progressively increases (Table 12), moving from zoisite to the Pb zoisite synthetic phase.   With the increasing substitution of Ca by A 2+ , O4-O6-O5 angle shows a quite limited change, moving from zoisite to zoisite-(Pb), with a more pronounced decrease when moving to synthetic Sr-zoisite and synthetic Pb-zoisite, in agreement with the expansion of A1 cavity along a axis. The T2-O8-M3 angle gradually increases, in agreement with the expansion of A2 cavity along c. Accordingly, the O2-O8 distance, involving two atoms placed on opposite sides of A2 cavity (Figure 8), progressively increases (Table 12), moving from zoisite to the Pb zoisite synthetic phase.
The quite small increase in b unit cell parameter can be explained according to [6]: Entering of Pb in A cavities in synthetic Pb zoisite-like phase (see Figure 3 in [6]) "stretches" the M12 octahedral chains along b, contemporarily "kinking" the same octahedral chains, therefore resulting in a smaller net expansion along b.
The crystal structure of hancockite was determined by [38], on material from Franklin, New Jersey, described as small, poorly formed, scarcely crystalline, and probably partially metamict. Chemical analyses [8] performed on crystals from the same locality were assumed in [38] as representative of the material. More recent EPMA chemical data on Franklin hancockite were reported by [43], on euhedral, bright-red, second-generation crystals, showing relevant differences compared with [8] chemical data.
We report in the present study a more reliable multi-technique study of hancockite from Jakobsberg, including EPMA, Raman, X-ray single-crystal, and powder diffraction data obtained on the same material. Crystal structural data of Jakobsberg hancockite largely confirmed results reported in [38]. Hancockite is isotypic with epidote, and its crystal structure (Figure 9) can thus be described through two distinct octahedral chains, a first one made up by edge-sharing regular M1 octahedra, with laterally linked M3 distorted octahedra, and a second one by regular M2 octahedra. The quite small increase in b unit cell parameter can be explained according to [6]: Entering of Pb in A cavities in synthetic Pb zoisite-like phase (see Figure 3 in [6]) "stretches" the M12 octahedral chains along b, contemporarily "kinking" the same octahedral chains, therefore resulting in a smaller net expansion along b.
The crystal structure of hancockite was determined by [38], on material from Franklin, New Jersey, described as small, poorly formed, scarcely crystalline, and probably partially metamict. Chemical analyses [8] performed on crystals from the same locality were assumed in [38] as representative of the material. More recent EPMA chemical data on Franklin hancockite were reported by [43], on euhedral, bright-red, second-generation crystals, showing relevant differences compared with [8] chemical data.
We report in the present study a more reliable multi-technique study of hancockite from Jakobsberg, including EPMA, Raman, X-ray single-crystal, and powder diffraction data obtained on the same material. Crystal structural data of Jakobsberg hancockite largely confirmed results reported in [38]. Hancockite is isotypic with epidote, and its crystal structure (Figure 9) can thus be described through two distinct octahedral chains, a first one made up by edge-sharing regular M1 octahedra, with laterally linked M3 distorted octahedra, and a second one by regular M2 octahedra. Octahedrally coordinated cations larger than Al 3+ , such as Fe 3+ and Mn 3+ , preferentially occupy the M3 site, entering in M1 only with Xep > 0.6 [47]. M2 is the smallest and most regular of the three octahedrally coordinated sites. The two M1 and M2 chains are laterally linked through SiO4 and Si2O7 groups, thus forming a smaller A1 and a larger A2 cavity (Figure 9), the former hosting Ca and the latter both Ca and larger cations such as Figure 9. Crystal structure of hancockite as seen along b. The mineral is isotypic with P2 1 /m epidotes, with chains of M1 octahedra with laterally linked distorted M3 octahedra, and chains of M2 octahedra, both running along b. Octahedral chains are interconnected along a and c directions through corner sharing disilicate groups and isolated T3 tetrahedra, respectively.
Octahedrally coordinated cations larger than Al 3+ , such as Fe 3+ and Mn 3+ , preferentially occupy the M3 site, entering in M1 only with X ep > 0.6 [47]. M2 is the smallest and most regular of the three octahedrally coordinated sites. The two M1 and M2 chains are laterally linked through SiO 4 and Si 2 O 7 groups, thus forming a smaller A1 and a larger A2 cavity (Figure 9), the former hosting Ca and the latter both Ca and larger cations such as Pb, Sr, and REE. Geometrical features of coordination polyhedra in hancockite are reported in Tables 9 and 13.  Table 13. Comparison of mean bond distances, polyhedral volume (A 3 ), and distortion parameters [28] (quadratic elongation λ bond angle variance σ 2 ) for coordination polyhedra in hancockite. No significative change in tetrahedral units is found with respect to the values reported for T units geometry in [47]. Concerning the octahedral units, M2 is, as expected [47], the smaller and more regular of the three polyhedra, whereas M1 shows a barely detectable degree of distortion only, if compared with the definitely larger and more distorted M3 polyhedron. Substitution of Ca 2+ with Pb 2+ , with [7] ionic radii 1.06 Å and 1.23 Å, respectively [48], leads to a distinct increase of the A2 polyhedron size, leaving instead the largely unaffected A1 polyhedron (Figure 7). The A2 coordination polyhedron in hancockite does not show any asymmetry in the spatial distribution of bonds compatible with the presence of the Pb 2+ lone pair effect.

Relationships with Other Natural and Synthetic Phases
Following literature data [1,2,47], zoisite-(Pb) and hancockite can be regarded as the coexisting iron-poor, high-temperature and the iron-rich, low-temperature phases, respectively. According to [3,4], zoisite-(Pb), together with zoisite, cannot be included in the epidote supergroup, which includes phases with monoclinic symmetry only. It seems, therefore, proper to assess the definition of a new zoisite group, to be properly submitted to the IMA-CNMMN. Possible new phases, apart from zoisite and zoisite-(Pb), can be predicted for this group. The Sr analogue of zoisite-(Pb), with the ideal chemical formula CaSrAl 3 (SiO 4 )(Si 2 O 7 )O(OH), seems conceivable, as well as the minerals with Sr and Pb dominant in both A1 and A2 sites, suggested by [5,6], respectively.
Author Contributions: K.E. provided the studied specimens and performed preliminary analyses; N.P., D.M., P.V. and F.Z. performed the experiments; N.P., D.M., P.V. and F.Z. analyzed the chemical and crystallographic data; N.P. wrote the paper with input from all the other authors. All authors have read and agreed to the published version of the manuscript.