Title: Lead-antimony sulfosalts from Tuscany (Italy). XXI. Bernarlottiite, Pb12(As10Sb6)Σ16S36, a new N = 3.5 member of the sartorite homologous series from the Ceragiola marble quarry, Apuan Alps: occurrence and crystal structure

Running title: Bernarlottiite, a new member of the sartorite series

Plan of the article:Abstract1. Introduction2. Occurrence and mineral description

2.1. Occurrence and physical properties of bernarlottiite2.2. Chemical data2.3. Crystallography

3. Crystal structure description3.1. General organization3.2. Cation coordinations and site occupancies3.3. Polymerization of (Sb/As) sites

4. Discussion4.1. Crystal-chemistry of bernarlottiite4.2. Chemical variability of “baumhauerites” and the occurrence of superstructures4.3. Building operators in baumhauerite homeotypes and other homologues

5. ConclusionReferences

Corresponding author: Cristian BiagioniComputer: PCOS: WindowsSoftware: WordNumber of characters (including spaces): 44204

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Lead-antimony sulfosalts from Tuscany (Italy). XXI. Bernarlottiite, Pb12(As10Sb6)Σ16S36, a new N = 3.5 member of the sartorite homologous series from the Ceragiola marble quarry: occurrence and crystal structure

PAOLO ORLANDI1, CRISTIAN BIAGIONI1,*, ELENA BONACCORSI1, YVES MOËLO2 and WERNER H. PAAR3

1Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, I-56126 Pisa, Italy2Institut des Matériaux Jean Rouxel, UMR 6502, CNRS, Université de Nantes, 2, rue de la Houssinière, 44322 Nantes Cedex 3, France3Department of Chemistry and Physics of Materials, University, Hellbrunnerstr. 34, A-5020 Salzburg, Austria

*Corresponding author, e-mail: biagioni@dst.unipi.it

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Abstract: The new mineral species bernarlottiite, Pb12(As10Sb6)Σ16S36, has been discovered in

cavities of the Early Jurassic marbles from the Ceragiola quarry, Seravezza, Apuan Alps, Tuscany,

Italy. Its name honours Bernardino Lotti (1847–1933) for his significant contribution to the

knowledge of the geology of Tuscany and to the development of the Tuscan mining industry. It

occurs as lead-grey acicular crystals up to 1 mm in length and few μm in width, with a metallic

luster, associated with Sb-rich sartorite. Under the ore microscope, bernarlottiite is white with

abundant red internal reflections; pleochroism is weak in air, with shades of grey-blue.

Anisotropism is distinct to strong, with greyish-bluish rotation tints. Reflectance percentages for the

four COM wavelengths are [Rmin, Rmax (%), (λ)]: 30.0, 37.5 (470 nm); 30.3, 37.3 (546 nm); 29.7,

36.8 (589 nm); and 29.3, 36.2 (650 nm). Electron-microprobe analyses, collected on two different

grains, gave (in wt%): Cu 0.09(16), Pb 48.89(1.26), As 17.48(22), Sb 11.36(10), S 23.11(32), total

100.93(1.38) (sample # 2987) and Cu 0.02(3), Pb 47.43(26), As 14.56(24), Sb 13.92(18), S

22.64(17), total 98.58(46) (sample # 3819). On the basis of ΣMe = 28 atoms per formula unit, the

chemical formulae are Cu0.07(12)Pb11.71(18)As11.59(21)Sb4.63(9)S35.78(48) and

Cu0.02(2)Pb11.92(6)As10.12(14)Sb5.95(8)S36.76(32) for samples # 2987 and # 3819, respectively. The main

diffraction lines, corresponding to multiple hkl indices, are [d in Å (relative visual intensity)]: 3.851

(s), 3.794 (s), 3.278 (s), 3.075 (s), 2.748 (vs), 2.363 (s), 2.221 (vs). The crystal structure study gives

a triclinic unit cell, space group P1 , with a = 23.704(8), b = 8.386(2), c = 23.501(8) Å, α = 89.91(1),

β = 102.93(1), γ = 89.88(1)°, V = 4553(2) Å3, Z = 3. The crystal structure has been solved and

refined to R1 = 0.088 on the basis of 7317 reflections with Fo > 4σ(Fo). Bernarlottiite is a new N =

3.5 homeotype of the sartorite homologous series, with a 3a superstructure relatively to that of

primitive baumhauerite. Its crystal structure can be described as being formed by 1:1 alternation of

sartorite-type (N = 3) and dufrénoysite-type (N = 4) layers along c, connected by Pb atoms with

tricapped trigonal prismatic coordination. Each layer results from the stacking of two types of

ribbons along a, a centrosymmetric one alternating with two acentric ones. The three main building

operators of the structure are 1) the interlayers As-versus-Pb crossed substitution, stabilizing the

combined N = (3,4) baumhauerite homologue, 2) the inter-ribbon Sb partitioning in the sartorite

layer, with “symmetrization” of the Sb-rich ribbon, that induces the 3a superstructure, and 3) the

common (As,Sb) polymerization through short (As,Sb)–S bonds.

Key-words: bernarlottiite; sartorite homologous series; new mineral species; sulfosalt; lead;

antimony; arsenic; crystal structure; building operators; Apuan Alps.

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1. IntroductionMineral species belonging to the sartorite homologous series (Table 1), defined in details by

Makovicky (1985), after the basic comparative crystallographic study of Le Bihan (1962), are

structurally characterized by the regular stacking of one or two types of slabs (N = 3 and 4). This

mineral group is an interesting field of research owing to its complex crystal-chemistry (Moëlo et

al., 2008), allowing the description of several new mineral species. In this respect, the most prolific

deposit is the Lengenbach quarry, Binn Valley, Switzerland, being the type locality for nine species

within the sartorite group. It is followed by the Apuan Alps hydrothermal ore deposits, representing

the type localities for four new mineral species. Whereas sartorite group members have been known

from Lengenbach since a long time (e.g., Rath, 1864), the presence of these minerals in the

hydrothermal veins from Apuan Alps was identified only in the last thirty-five years. Two different

kinds of occurrence are known, i.e. the baryte + pyrite ore deposits from southern Apuan Alps (i.e.

the Pollone and Monte Arsiccio mines) and the cavities of the marble quarries near the town of

Seravezza. The first kind of occurrence represents the type locality for boscardinite (Orlandi et al.,

2012; Biagioni & Moëlo, 2016), carducciite (Biagioni et al., 2014), and polloneite (Topa et al.,

2015b). In addition, twinnite (also in a thallium-rich variety) and veenite have been recently

identified. The cavities of the marble quarries from the Seravezza area have been known since the

description of guettardite by Bracci et al. (1980). In addition, Orlandi et al. (1996) and Orlandi &

Criscuolo (2009) described the identification of “Sb-rich baumhauerite” and sartorite. Whereas the

latter has not been completely characterized yet, the former has been accurately studied collecting

single-crystal X-ray diffraction and electron-microprobe data.

Single-crystal X-ray diffraction data of this “Sb-rich baumhauerite” clearly indicated the

presence of a 3 × 7.9 Å superstructure periodicity, indicating homeotypic relationships with true

primitive baumhauerite and pointing to a distinction between baumhauerite itself and this Sb-rich

derivative, which has been named bernarlottiite. The mineral and its name have been approved by

the IMA-CNMNC, under the number 2013-133 (Orlandi et al., 2014). The holotype specimen is

deposited in the mineralogical collection of the Museo di Storia Naturale, Università di Pisa, Via

Roma 79, Calci, Pisa (Italy), under catalogue number 19687. The name is in honour of Bernardino

Lotti (1847–1933) for his significant contribution to the knowledge of the geology of Tuscany and

to the development of the Tuscan mining industry. Indeed, his studies contributed to the discovery

and exploitation of the Niccioleta, Boccheggiano, and Gavorrano world-class pyrite ore deposits, as

well as of other important Tuscan mines. He greatly contributed to the geological mapping of

Tuscany, publishing four books on the geology of Elba Island, the Massa Marittima mining district,

Tuscany, and Umbria. In addition, Bernardino Lotti was author of more than 200 papers. Together

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with Domenico Zaccagna (1851–1940), he contributed to the geological mapping of the Apuan

Alps. Marinelli (1983) reported a list of works published by Lotti. In naming the new mineral,

“bernarlottiite” was preferred to “lottiite”, in order to avoid any confusion with the member of the

cancrinite group liottite.

This paper reports the description of the occurrence of bernarlottiite and its crystal structure,

discussing its relationships with the other members of the sartorite homologous series.

2. Occurrence and mineral description2.1. Occurrence and physical properties of bernarlottiite

Bernarlottiite was collected in cavities of the Early Jurassic marble outcropping in the

Ceragiola area, Seravezza marble quarries, Apuan Alps, Tuscany, Italy. These marble outcrops

belong to the Apuane Unit (e.g., Fellin et al., 2007), a tectonic unit formed by a Paleozoic basement

overlain by a Triassic – Tertiary metasedimentary sequence, metamorphosed up to the greenschist

facies and affected by two main deformation events (D1 and D2 of Carmignani & Kligfield, 1990).

The mineralized cavities have an elongated, sometimes s-shaped cross-section, only a few mm to

few cm in width and up to 30 cm high; the length can reach several meters. These cavities lies on

definite horizons related to the S1 schistosity surface of the D1 tectonic phase, which was refolded

during the D2 event (Orlandi et al., 1996). In this kind of occurrence, many lead-antimony-arsenic

sulfosalts have been identified, including guettardite (Bracci et al., 1980), robinsonite (Franzini et

al., 1992), izoklakeite (Orlandi et al., 2010), zinkenite, boulangerite, sartorite, semseyite, and

jordanite (Orlandi et al., 1996). Seravezza is also the type locality for two additional lead sulfosalts,

moëloite (Orlandi et al., 2002) and disulfodadsonite (Orlandi et al., 2013a).

Bernarlottiite was identified in few specimens collected in the Ceragiola area. It occurs as

mm-sized thin acicular crystals, elongated [010], lead-grey in color (Fig. 1), with a black streak and

a metallic luster. It is brittle, without any evident cleavage. Owing to the very small size of the

available crystals, micro-hardness was not measured. In plane-polarized incident light, bernarlottiite

is white in colour, with abundant red internal reflections. Pleochroism is weak in air, whereas it is

distinct in oil, with shades of grey-blue. Bireflectance is distinct. Between crossed polars,

bernarlottiite is distinctly to strongly (in oil) anisotropic, with greyish to bluish rotation tints.

Twinning revealed by the X-ray diffraction study was not observed. Reflectance values (WTiC as

standard) were measured in air and are given in Table 2 and shown in Figure 2.

In the studied specimen, bernarlottiite is associated with Sb-rich sartorite; this latter phase

has not been fully characterized yet. The crystallization of these minerals is related to the circulation

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of hydrothermal fluids in the cavities of the marbles during the Tertiary Alpine tectono-

metamorphic event.

2.2. Chemical data

Two grains of bernarlottiite (# 2987 and 3819, respectively) were analyzed with a

CAMECA SX50 electron microprobe (BRGM-CNRS-University common laboratory, Orléans,

France) operating in WDS mode. The operating conditions were: accelerating voltage 20 kV, beam

current 20 nA, beam size 5 μm. Standards (element, emission line) were: pyrite (S Kα), galena (Pb

Mα), stibnite (Sb Lα), AsGa (As Lα), and metal Cu (Cu Kα).

Electron microprobe data for bernarlottiite are given in Table 3. On the basis of ΣMe = 28

atoms per formula unit, the chemical formula of bernarlottiite can be written as

Cu0.07(12)Pb11.71(18)As11.59(21)Sb4.63(9)S35.78(48) and Cu0.02(2)Pb11.92(6)As10.12(14)Sb5.95(8)S36.76(32) for grains #2987

and 3819, respectively. The S excess shown by the analysis on grain #3819 is not supported by the

solution of the crystal structure (see below). The small Cu content can be subtracted according to

the substitution rule Cu+ + (As,Sb)3+ = 2 Pb2+. The As/(As+Sb) atomic ratio in bernarlottiite varies

between 0.63 (#3819) and 0.71 (#2987), corresponding to the two idealized compositions

Pb12As11.5Sb4.5S36 and Pb12As10Sb6S36.

2.3. Crystallography

The X-ray powder diffraction pattern of bernarlottiite was collected using a 114.6 mm

Gandolfi camera with Ni-filtered Cu Kα radiation. The observed pattern is reported in Table 4,

where it is compared with the calculated one obtained through the software PowderCell (Kraus &

Nolze, 1996) using the structural model described below. Owing to the multiplicity of indices for

the majority of the diffraction lines, the unit-cell parameters were not refined.

Due to the very small size of available crystals, intensity data of bernarlottiite were collected

at the XRD1 beamline at the Elettra synchrotron radiation facility, Basovizza, Trieste, Italy. Data

collection were performed by rotating the crystal around one axis by Δφ = 1° and collecting the

reflections by means of a 165 mm MarCCD detector with a working distance of 50 mm. Reflections

were integrated and intensities corrected for Lorentz-polarization and background effects using the

HKL package of software (Otwinowski & Minor, 1997). The statistical tests on the distribution of |E|

values (|E2 – 1| = 0.995) suggested the occurrence of a centre of symmetry. The refined unit-cell

parameters are a = 23.704(8), b = 8.386(2), c = 23.501(8) Å, α = 89.91(1), β = 102.93(1), γ =

89.88(1)°, V = 4553(2) Å3, space group P1 . The a:b:c ratio is 2.827:1:2.802.

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The structure of bernarlottiite was solved by direct methods using Shelxs-97 (Sheldrick,

2008) and then refined through Shelxl-2014 (Sheldrick, 2008). Scattering curves for neutral atoms

were taken from the International Tables for Crystallography (Wilson, 1992). After having located

the heavier atoms (Pb and some Sb sites), the structure was completed through successive

difference-Fourier maps. The examination of the bond distances, as well as bond-valence balance,

calculated using the bond parameters given by Brese & O’Keeffe (1991), revealed the presence of

several mixed (Pb/Sb) and (Sb/As) sites and their site occupation factors were refined. Finally, the

occurrence of a twin axis [010] was introduced, giving a twin ratio of 72:28. After several cycles of

anisotropic refinement, the agreement factor R1 converged to 0.088 for 7317 reflections with Fo >

4σ(Fo). Details of the intensity data collection and crystal structure refinement are given in Table 5.

3. Crystal structure description3.1. General organization

Atomic coordinates, site occupancies, and equivalent isotropic displacement parameters of

bernarlottiite are given in Table 6. The unit-cell content is shown in Figure 3.

The general organization of bernarlottiite, as seen down b, is presented in Figure 4. This

mineral is a N(1,2) = 3,4 member of the sartorite homologous series and it is homeotypic with

baumhauerite, argentobaumhauerite, boscardinite, and écrinsite (Orlandi et al., 2012; Biagioni &

Moëlo, 2016; Topa & Makovicky, 2016; Topa et al., 2016). Its crystal structure can be described as

formed by the 1:1 alternation along c of layers, one of the sartorite type (N = 3), the second one of

the dufrénoysite type (N = 4). These layers are connected through Pb atoms with tricapped trigonal

prismatic coordination. The twinning may correspond to layer stacking disorder, for instance (3, 4,

4), i.e. liveingite-type homologue in the ···3-4-3-4-3-4··· sequence.

Within the layers, all sites correspond to pure Pb, As, Sb, or mixed (Pb/Sb) and (As/Sb)

positions. Whereas in baumhauerite and boscardinite each type of layer is formed by one kind of

oblique ribbon, two different kinds of oblique ribbons occur in each layer of bernarlottiite (Fig. 4).

The first one is centrosymmetric, whereas the second one is acentric. Both N = 3 and N = 4 layers

are formed by one centrosymmetric ribbon and two acentric ribbons, that induce the 3a

superstructure relatively to primitive, Sb-free baumhauerite.

3.2. Cation coordinations and site occupancies

Forty-two independent metal sites and fifty-four S positions have been located in the crystal

structure of bernarlottiite. Table 7 gives average bond distances and bond-valence sums, calculated

according to the bond parameters of Brese & O’Keeffe (1991).

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Table 8 gives the chemical distribution of metal sites. There are sixteen pure Pb positions,

four mixed (Pb/Sb) sites (two with Pb > Sb and two with Sb > Pb), and twenty-two Me3+ sites (Me3+

= As, Sb). Pure lead sites display coordination numbers ranging from six to nine, corresponding to

trigonal prismatic to tricapped trigonal prismatic coordination. Pb1 to Pb12, at the layer junction,

are “standing” tricapped trigonal prisms, with average bond lengths ranging from 3.161 (Pb8) and

3.232 Å (Pb11), and bond-valence sums between 1.74 (Pb7) and 1.88 valence unit (v.u.) (Pb11).

Pb14 to Pb17, within the dufrénoysite type layer, display distorted octahedral (Pb14) and

monocapped trigonal prismatic coordination (Pb15 to Pb17).

The four mixed (Pb/Sb) positions are equally partitioned between sartorite and dufrénoysite

type layers. Actually, Pb-dominant sites (i.e., Pb18 and Pb19 sites) are located within the N = 3

layer and display six- (Pb19) and seven-fold (Pb18) coordination. The Sb-dominant sites (Sb13 and

Sb33) are hosted within the N = 4 layer. Sb13 has a distorted octahedral coordination, with two Me–

S distances shorter than 2.70 Å, three distances ranging between 2.70 and 3.10 Å, and a sixth

definitely longer distance at 3.34 Å. The bond-valence sum at the Sb13 site is 2.65 v.u., to be

compared with an expected value of 2.77 v.u. Sb33 shows a similar six-fold coordination

environment. However, in addition to the two bond distances shorter 2.70 Å, there are only two

distances in the range 2.70 – 3.10 Å, whereas the two remaining Me–S bonds are longer (i.e., 3.37

and 3.52 Å). The bond-valence sum (2.59 v.u.) agrees with the expected one (2.68 v.u.).

The twenty-two Me3+ sites can be further subdivided into eight pure As positions, four pure

Sb sites, and ten mixed (As/Sb) positions (eight with As > Sb and two with Sb > As). Pure As sites

display the typical three-fold pyramidal coordination, with average <As–S> distance (taking into

account distances shorter than 2.70 Å) ranging between 2.257 (As25) and 2.290 (As24) Å. The

coordination sphere is usually completed by two additional longer bonds. The pure Sb sites usually

display also the typical trigonal pyramidal coordination, with average bond distances (taking into

account Sb–S distances shorter than 2.70 Å) varying between 2.515 (Sb31) and 2.549 Å (Sb38).

The only exception is represented by the Sb21 site, having only two distances shorter than 2.70 Å,

with two additional bonds between 2.75 and 2.85 Å. The coordination environment of the pure Sb

positions is completed by three (or two, for Sb31) S atoms, giving rise to Sb-centered distorted

octahedra. Finally, the ten mixed (As/Sb) sites show the trigonal pyramidal coordination completed

by two or three longer Me–S bonds. The average <Me–S> distances are related to the (As:Sb)at.

ratio, ranging from 2.285 for the As22 site (s.o.f. As0.88Sb0.12) to 2.489 Å for the Sb36 site (s.o.f.

Sb0.71As0.29). According to Table 7, the bond-valence sums of all (As/Sb) positions range between

2.90 (Sb21) and 3.33 v.u. (As20).

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3.3. Polymerization of (Sb/As) sites

Within the sartorite (N = 3) and dufrénoysite (N = 4) type layers, if only the shortest (=

strongest) Me3+–S distances are considered (i.e. distances shorter than 2.70 Å, following the

approach of Moëlo et al., 2012), the organization of Me3+ sites into finite Me3+mSn chain fragments

(hereafter “polymers”) can be described. By using such a cut-off distance, As and Sb atoms usually

display the classic triangular pyramidal coordination. In the crystal structure of bernarlottiite, the

exceptions are represented by the central portions of the two kinds of ribbons within the N = 4 type

layer, and in the central portion of the centrosymmetric ribbon within the N = 3 type layer, with Sb

or mixed (Sb,Pb) positions having only one or two short distances.

In the N = 3 layers, the two different kinds of oblique ribbons are indicated as Sc and Sa

(subscript c and a indicating the centrosymmetric and non-centrosymmetric natures of the oblique

ribbons, respectively). Figure 5 (left) represents the selection of one Sc oblique ribbon. There are

two dualities in cation positions:

1. Sb38 is a mean position between S38 and S53 (sub-position “down” – Sb38–S38 =

2.729 Å; “up” – Sb38–S53 = 2.688 Å);

2. in two neighbouring (Pb,Sb)19 sites, with quite equal occupancies, filling one position

by Sb (for instance Sb “up”) will induce the filling of the other position by Pb (Pb

“down”), to optimize the local valence equilibrium.

From one side of the ribbon to the other, the choice of combination of Sb38 “up” with Sb19

“up” will imply Pb19 “down” followed by Sb38 “down”, i.e. the polymer sequence AsS3 →

(Sb,As)3S6 → (Sb,As)3S7. The combination of Sb38 “up” with Sb19 “down” will give the polymer

sequence AsS3 → (Sb,As)2S4 → (Sb,As)4S9.

In one Sa oblique ribbon (Fig. 5, right), the main filling of (Pb,Sb)18 by Pb gives two

polymers, (Sb,As)3S7 and (Sb,As)4S9. With Sb18 present, there is only one polymer (Sb,As)7S16.

As in other structures, Sb prefers to be partitioned within the central part of the ribbon,

whereas As is preferentially hosted in the marginal group. Indeed, the higher As/(As+Sb)at. ratio

shown by bernarlottiite with respect to boscardinite and (Tl,As)-rich boscardinite favours the As-to-

Sb substitution at the isolated trigonal pyramids (Sb-dominant in boscardinite and As-dominant in

(Tl,As)-rich boscardinite – Orlandi et al., 2012; Biagioni & Moëlo, 2016).

The oblique ribbons occurring in the dufrénoysite type layer (N = 4) are shown in Figure 6.

The centrosymmetric Dc ribbon (Fig. 6, left) shows lateral [As2(As,Sb)]Σ3S7 chain fragments; the

central portion of the ribbon is occupied by two mixed (Sb,Pb) sites, i.e. Sb13 and Sb33.

Consequently, the size of the polymer is determined by the presence or absence of Sb on these

positions. These sites have only two Me–S distances shorter than 2.70 Å, probably as a result of

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their average nature. Both sites have two longer Me–S in the range between 2.70 and 3.00 Å. Sb13

has two S atoms at 2.78 (S14) and 2.80 Å (S23), respectively, while Sb33 is at 2.76 and 2.90 Å

from S9 and S23, respectively. In our opinion, Sb33–S9 bond could be favoured, because a slight

displacement of Sb from the refined position allows a correct three-fold coordination; on the

contrary, owing to the similarity in bond distances between Sb13–S14 and Sb13–S23, both

solutions could be equally possible. If the first solution occurs, assuming a full Sb occupancy at

both Sb13 and Sb33, the polymer [As4(As,Sb)2Sb2]Σ8S17 can be defined. The other configuration

gives rise to the polymer [As4(As,Sb)2Sb4]Σ10S20. The Da ribbon (Fig. 6, right) is composed by two

polymers, mutually perpendicular each other, with metals located on the opposing sides of the

ribbon. The two chain fragments are [As2(As,Sb)(Sb,As)]Σ4S9 and [As(As,Sb)2Sb]Σ4S9. In addition,

the Sb21 site can belong to both chains. Indeed, Sb21 is an average position, with only two Me–S

distances shorter than 2.70 Å. It could be alternatively bonded to S19 or S16. In the first case, a

linear [As(As,Sb)2Sb2]Σ5S11 polymer occurs; in the other case, a branched chain [As2(As,Sb)

(Sb,As)Sb]Σ5S11 can be identified.

4. Discussion4.1. Crystal-chemistry of bernarlottiite

The crystal-chemical formula of bernarlottiite, as obtained through the refinement of its

crystal structure, is Pb11.93As10Sb6.07S36 (Z = 3), with the relative error on the valence equilibrium

Ev(%), as defined in the footnote of Table 3, of +0.1. With respect to the chemical data, the formula

derived from the crystal structure refinement agrees with sample #3819.

Taking into account electron-microprobe data, the homologue order of bernarlottiite can be

calculated according to Makovicky & Topa (2015), resulting in N = 3.47 and 3.49 for samples

#2987 and 3819, respectively, in very good agreement with the expected value N = 3.5. Indeed, as

stated above, the crystal structure of bernarlottiite displays the 1:1 alternation, along c, of two kinds

of layers, sartorite type (N = 3) and dufrénoysite type (N = 4). Both layer types are formed by two

kinds of ribbons. In the sartorite type layer, the centric Sc and acentric Sa ribbons have chemical

composition [Pb4(Pb1.02Sb0.98)Σ2(As3.60Sb2.40)Σ6.00S16]-1.02 and [Pb4(Pb0.81Sb0.19)Σ1.00(As4.64Sb2.36)Σ7.00S16]-0.81,

giving an overall composition of the N = 3 layer corresponding to

[Pb12(Pb2.64Sb1.36)Σ4(As12.88Sb7.12)Σ20.00S48]-2.64. The dufrénoysite type layer is formed by two ribbons Dc

and Da having chemical composition [Pb6.00(Sb2.86Pb1.14)Σ4(As5.68Sb0.32)Σ6.00S20]+0.86 and

[Pb7.00(As5.72Sb3.28)Σ9.00S20]+1. The overall composition of the N = 4 layer is

[Pb20(Sb2.86Pb1.14)Σ4(As17.12Sb6.88)Σ24.00S60]+2.86. Consequently, the chemical formula of bernarlottiite is

Pb32(Sb4.22Pb3.78)Σ8(As30.00Sb14.00)Σ44.00S108. On the basis of the general formula Me8NS8N+8 (e.g.,

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Makovicky & Topa, 2015), with N = 3.5, it could be written as

Pb10.67(Sb1.41Pb1.26)Σ2.67(As10.00Sb4.67)Σ14.67S36 (Z = 3).

The simplified chemical formula of the sartorite-type layer is close to Pb5Me3+7S16, against

Pb4Me3+8S16 for ideal sartorite; that of the dufrénoysite-type layer is Pb7Me3+

9S20, against Pb8Me3+8S20

for ideal dufrénoysite (Table 8). In other words, to minimize the distorsion between the two layers,

the large cation Pb2+ partly substitutes As3+ in the ideally As-pure sartorite layer, while, on the

contrary, the reverse substitution operates in the dufrénoysite-type layer, also permitting to respect

the valence equilibrium. It is a clear example of interlayer crossed-substitution rule, i.e. As3+sart +

Pb2+dufr → Pb2+

sart + As3+dufr.

Considering the partitioning of As and Sb between the two kinds of layers, the As/(As+Sb) at.

ratio is 0.603 and 0.637 in the sartorite and dufrénoysite type layers, respectively. In the two kinds

of ribbons forming the N = 3 layer, the As/(As+Sb)at. ratio indicates the preferential partitioning of

Sb in the Sc ribbon (atomic ratio = 0.516) with respect to the Sa ribbons (atomic ratio = 0.645). In

the dufrénoysite layer, on the contrary, there is no significant difference between the acentric and

centric ribbons, having As/(As+Sb)at. ratios of 0.636 and 0.641, respectively.

This inter-ribbon partitioning in the sartorite layer has an important consequence: the

“symmetrization” of the Sb-rich ribbon, while all ribbons are dissymmetric in Sb-free baumhauerite

(as well as in dufrénoysite – Ribar et al., 1969). Such a partial ribbon “symmetrization” by Sb

enrichment appears as the essential crystal chemical factor for the formation of a new baumhauerite

homeotype by stabilization of a 3a superstructure.

4.2. Chemical variability of “baumhauerites” and the occurrence of superstructures

Bernarlottiite is a new addition to the N = 3.5 homeotypes within the sartorite homologous

series. Baumhauerite was originally described as a pure Pb-As sulfosalt from the Lengenbach

quarry, Binn Valley, Switzerland (Solly & Jackson, 1902); Laroussi et al. (1989), examining

minerals belonging to the sartorite series from this Swiss locality, found less than 0.5 wt% Sb in

baumhauerite, corresponding to an As/(As+Sb)at. ratio close to 0.99. Similarly, baumhauerite from

Moosegg, Salzburg, Austria, was Sb-free (Topa & Makovicky, 2016).

The crystal-chemical studies of N = 3.5 members of the sartorite group highlighted three

different kinds of substitutions:

a) the heterovalent substitution Ag+ + (As/Sb)3+ = 2 Pb2+;

b) the heterovalent substitution Tl+ + (As/Sb)3+ = 2 Pb2+;

c) the homovalent substitution As3+ = Sb3+.

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The occurrence of Ag in baumhauerite was accurately described by Laroussi et al. (1989)

who reported two types of baumhauerite in syntactic lamellar intergrowth, i.e. Ag-free and Ag-rich

(~ 1.5 wt%). Pring et al. (1990) pointed out the occurrence of a 2a superstructure (actually a 2c

superstructure, assuming the axial setting given in Table 1), naming this new homeotype

baumhauerite-2a. The appearance of the superstructure reflections was related to some kind of

cation ordering; this hypothesis was confirmed by Topa & Makovicky (2016) who solved the

crystal structure of baumhauerite-2a and renamed it as argentobaumhauerite. Indeed, the doubling

of the c parameter is related to the occurrence of two different kinds of N = 4 slabs, displaying

different degrees of substitution of As and Pb by Ag. In addition, Pring & Graeser (1994) observed

the occurrence of a pseudo-orthorhombic 3c phase (3a in the axial setting of those authors).

Thallium was reported in “baumhauerites” from Lengenbach by Laroussi et al. (1989) in

only small amount, up to 0.65 wt% in argentobaumhauerite. The recent findings of boscardinite

(Orlandi et al., 2012) and écrinsite (Topa et al., 2016) allowed the description of the first

homeotypes in which Tl is an essential component. In addition, both mineral species have

significant Sb substituting for As, with As/(As+Sb)at. ratios ranging from 0.55 in écrinsite (Topa et

al., 2016) down to 0.21-0.31 in boscardinite (Orlandi et al., 2012; Biagioni & Moëlo, 2016).

Boscardinite is actually the first N = 3.5 homeotype in which Sb dominates over As.

The very first evidences of high Sb contents in “baumhauerites” were given by Jambor

(1967) who found an As:Sb atomic ratio close to 1 in samples from Madoc, Ontario, Canada.

Further chemical analyses indicated a slight dominance of Sb over As, with Sb-to-As ratios of 1.03

and 1.12 in the two studied samples (Jambor et al., 1982). The occurrence of Sb-bearing and Sb-

rich baumhauerite was reported by other authors, e.g., Robinson & Harris (1987) who found an

As/(As+Sb)at. ratio of 0.86 in a “baumhauerite” from Quiruvilca, Perù. Dunn (1995) reported the

occurrence of an antimonian baumhauerite from Sterling Hill, New Jersey, USA; its As/(As+Sb) at.

ratio is 0.715, close to the values found for bernarlottiite, i.e. 0.63-0.71. It is worth noting that Dunn

(1995) observed the same 3a supercell found in bernarlottiite; consequently it is very likely that

antimonian baumhauerite from Sterling Hill is actually bernarlottiite.

4.3. Building operators in baumhauerite homeotypes and other homologues

Three main crystal-chemical factors operate for the building of the structure of bernarlottiite

and its differentiation from baumhauerite.

1. Interlayer As/Pb crossed-substitution favouring steric adjustment between the sartorite-

and the dufrénoysite-type layers. The Pb-enriched sartorite layer has a composition close

to Pb5As7S16, like in “baumhauerite-2a” (Engel & Nowacki, 1969). This interlayer steric

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adjustment also operates in liveingite (= rathite II), according to Engel & Nowacki

(1970): the sartorite layer has effectively the formula Pb5As7S16, although in the double

dufrénoysite layer the As/Pb ratio is a little bit too high (Pb6.75As9.25S20, ideally

Pb7.5As8.5S20 for the charge balance). Such a crystal-chemical mechanism may be the

main factor minimizing the combination energy of the N = 3 and 4 layers relatively to a

mixture of primitive homologues sartorite and dufrénoysite.

2. Polymerization of Me3+–S short bonds reflects the steric adjustment of Me3+-rich ribbons

to columns or slabs of standing trigonal prismatic Pb atoms (prism axis parallel to the

elongation). An increase of the As content relatively to Sb as well Pb induces a general

shortening of the polymers (Doussier et al., 2008).

3. Sb-versus-As inter-ribbon partitioning, with symmetrization of the Sb-rich ribbon, which

controls the 3a superstructure of bernarlottiite. In Sb- and Tl-free species, all ribbons are

dissymmetric. On the contrary, with a high Sb/As atomic ratio, the symmetrization is

complete, e.g., in boscardinite, a (Tl,Sb)-rich homeotype of baumhauerite (Orlandi et al.,

2012), as well as in twinnite (Makovicky & Topa, 2012) and guettardite (Makovicky et

al., 2012), two Sb-rich homeotypes of sartorite.

In synthetic Sb-pure sartorite members BaSb2S4 (Cordier et al., 1984) and BaSb2Se4 (Cordier

& Schaefer, 1979), ribbons are necessary centrosymmetric (no Sb/As or Pb/(As,Sb) mixing). It is

also the case in Sb dufrénoysite derivatives Ba3Sb4.667S10 and Ba2.62Pb1.39Sb4S10 (Choi & Kanatzidis,

2000), although with a small dissymmetric partitioning of Pb and Ba in this last compound. In

philrothite (Bindi et al., 2015), owing to the replacement of 2 Pb by (Tl + Sb), there is no Tl within

the ribbon, that induces centrosymmetry.

5. ConclusionBernarlottiite is the first N(1,2) = 3,4 member of the sartorite homologous series having a 3a

superstructure. Thus, the pair baumhauerite – bernarlottiite is a new example in the group of

sulfosalts related the PbS or SnS archetypes where a small change in the chemistry (i.e., the Sb/As

ratio here) gives rise to homeotypic pairs, controlling a crystallographic discontinuity between close

species. Indeed, the different partitioning of As and Sb in the crystal structures of sulfosalts can give

rise to superstructure reflections, e.g., as in the chabournéite – protochabournéite pair (Orlandi et

al., 2013b), the Sb-to-As substitution being related to an increase in the size of the polymeric

(Sb/As)mSn units, in agreement with Doussier et al. (2008).

Bernarlottiite structure enhance the role of three building operators: 1) the interlayer As-

versus-Pb crossed substitution, stabilizing the combined N = (3,4) baumhauerite homologue, 2) the

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inter-ribbon Sb partitioning in the sartorite layer, with “symmetrization” of the Sb-rich ribbon, that

induces the 3a superstructure, and 3) the common (As,Sb) polymerization through short (As,Sb) – S

bonds.

Bernarlottiite exemplifies the importance of an accurate crystal-chemical study of complex

sulfosalts. Indeed, the As-to-Sb substitution could give rise to isotypic series (e.g., the bournonite –

seligmannite and geocronite – jordanite pairs) or it could promote the appearance of new structural

configurations (e.g., occurrence of superstructure reflections, changes in space group symmetry)

and, consequently, it could favour the crystallization of new mineral species. The occurrence of

superstructures seems to be a phenomenon characteristic of several members of the sartorite

homologous series. In addition to bernarlottiite, several new minerals have been recently defined

(e.g., enneasartorite, hendekasartorite, heptasartorite) whose occurrence is related to chemical

changes. Finally, it is worth noting that polloneite (Topa et al., 2015b), a N = 4 homologue related

to dufrénoysite, presented a 3 × 7.9 Å superstructure apparently similar to that observed in

bernarlottiite. Consequently, the sartorite homologous series is probably one of the most prolific

research field today in sulfosalt systematics.

Acknowledgments: Stefano Conforti is thanked for providing us with the studied specimens.

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2015-074. CNMNC Newsletter No. 28, December 2015, page 1861. Mineral. Mag., 79, 1859-

1864.

Topa, D., Keutsch, F.N., Makovicky, E., Kolitsch, U., Paar, W. (2015b): Polloneite, IMA 2014-093.

CNMNC Newsletter No. 24, April 2015, page 249. Mineral. Mag., 79, 247-251.

Topa, D., Makovicky, E., Berlepsch, P., Stroeger, B., Stanley, C. (2015c): Hendekasartorite, IMA

2015-075. CNMNC Newsletter No. 28, December 2015, page 1861. Mineral. Mag., 79, 1859-

1864.

Topa, D., Stroeger, B., Makovicky, E., Berlepsch, P., Stanley, C. (2015d): Heptasartorite, IMA

2015-073. CNMNC Newsletter No. 28, December 2015, page 1861. Mineral. Mag., 79, 1859-

1864.

Topa, D., Kolitsch, U., Makovicky, E., Favreau, G., Stanley, C., Bourgoin, V., Bouilliard, J.-C.

(2016): Écrinsite, IMA 2015-099. CNMNC Newsletter No. 29, February 2016, page 204.

Mineral. Mag., 80, 199-205.

Sheldrick, G.M. (2008): A short history of SHELX. Acta Crystallogr., A64, 112-122.

18Orlandi et al.

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570

571

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Wang, J., Lee, K., Kovnir, K. (2015): Synthesis, crystal structure, and thermoelectric properties of

two new barium antimony selenides: Ba2Sb2Se5 and Ba6Sb7Se16.11. J. Mater. Chem., 3, 9811-

9818.

Wilson, A.J.C., Ed. (1992): International Tables for X-ray Crystallography, Volume C: Mathematical, physical and chemical tables. Kluwer Academic, Dordrecht, NL.

19Orlandi et al.

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Table captions

Table 1 – Members of the sartorite homologous series.

Table 2 – Reflectance data (%) for bernarlottiite in air.

Table 3 – Electron microprobe analyses of bernarlottiite: chemical composition as wt% and

chemical formula (in atoms per formula unit, apfu) on the basis of ΣMe = 28 apfu.

Table 4 –X-ray powder diffraction data for bernarlottiite. Intensities and dhkl were calculated using

the software PowderCell 2.3 (Kraus and Nolze, 1996) on the basis of the structural model given in

Table 4. The seven strongest reflections are given in bold. Only reflections with Icalc ≥ 10 were

reported, if not observed. Observed intensities were visually estimated (s = strong; m = medium;

mw = medium-weak; w = weak; vw = very weak).

Table 5 – Crystal data and summary of parameters describing data collection and refinement for

bernarlottiite.

Table 6 – Atomic coordinates, site occupation factors, and equivalente isotropic displacement

parameters (Å2) for bernarlottiite.

Table 7 – Average bond-distances (in Å) and bond-valence sums (in valence units) for metal sites

in bernarlottiite.

Table 8 – Metal site distribution within the crystal structure of bernarlottiite. Sc and Sa represent the

centric and acentric ribbons in the N = 3 layer, respectively; Dc and Da represent the centric and

acentric ribbons in the N = 4 layers.

Figure captions

Figure 1 – Bernarlottiite, black acicular crystals. Ceragiola area, Seravezza, Apuan Alps, Tuscany,

Italy. Collection Museo di Storia Naturale, Università di Pisa. Catalogue number 19687.

Figure 2 – Reflectance spectra of bernarlottiite. For sake of comparison, the reflectance spectra of

its Tl-Sb homeotype boscardinite (Orlandi et al., 2012) are shown.

Figure 3 – Unit-cell content of bernarlottiite, as seen down b.

Figure 4 – General organization of bernarlottiite, as seen down b. Dotted and dashed lines delimit

the N =3 and N = 4 ribbons, respectively. Red and blue lines indicate the centrosymmetric and

acentric ribbons, respectively.

Figure 5 – Polymeric organization of (Sb/As) atoms with S atoms (short bonds, thick dark green

lines) in the sartorite type layer. The two ribbons Sc (left) and Sa (right) are shown. Thick tie-lines

correspond to longer bonds, related to mean Sb positions, or mixed (Pb,Sb) sites. In Sc ribbon (left),

20Orlandi et al.

581

582

583

584

585

586

587

588

589

590

591

592

593

594

595

596

597

598

599

600

601

602

603

604

605

606

607

608

609

610

611

612

3940

the lower part indicates the two possible polymer combinations (separated by red tie-line),

according to the “up” or “down” positions of Sb atoms.

Figure 6 – Polymeric organization of (Sb/As) atoms with S atoms (short bonds, thick dark green

lines) in the dufrénoysite type layer. The two ribbons Dc (left) and Da (right) are shown.

21Orlandi et al.

613

614

615

616

617

4142

Table 1 – Members of the sartorite homologous series. Unit-cell parameters are given as AE (elongation axis), AL (layer stacking axis), and AR

(ribbon stacking axis).

Mineral Chemical formula AE (Å) AR (Å) AL (Å) Angles ≠ 90° V (Å3) S.G. Ref.N = 3,3 Sartorite PbAs2S4 4.19 7.89 19.62 648.6 P21/n [1]Guettardite Pb(Sb0.56As0.44)2S4 8.53 7.97 20.10 101.8 1337.3 P21/c [2]Twinnite Pb(Sb0.63As0.37)2S4 8.63 8.00 19.52 91.1 (AE/AR) 1347.4 P21/n [3]Heptasartorite Tl7Pb22As55S108 29.27 7.88 20.13 102.1 (AE/AL) 4537.9 P21/c [4]Enneasartorite Tl6Pb32As70S140 37.61 7.88 20.07 101.9 (AE/AL) 5818.6 P21/c [5, 6]Hendekasartorite Tl2Pb48As82S172 31.81 7.89 28.56 99.0 (AE/AL) 7076.4 P21/c [7]Pierrotite TlSb5S8 8.82 7.99 38.75 2728.9 Pna21 [8]Parapierrotite Tl(Sb,As)5S8 9.06 8.10 19.42 92.0 (AE/AR) 1423.0 Pn [9]Synth. BaSb2S4 8.99 8.20 20.60 101.4 (AE/AL) 1488.7 P21/c [10]Synth. BaSb2Se4 9.24 8.55 20.76 91.2 (AE/AR) 1639.4 P21/n [11]N = 3, 4 AE/AL AR/AL AE/AR

Baumhauerite Pb12As16S36 8.34 7.88 22.81 90.1 97.3 90.1 1488.8 P1 [12]Argentobaumhauerite AgPb10As17S36 8.47 7.91 44.41 84.6 86.5 89.8 2954.2 P-1 [12]Bernarlottiite Pb12(As10Sb6)Σ16S36 8.39 23.70 23.50 89.9 102.9 89.9 4553 P-1 [13]Écrinsite AgTl3Pb4(As11Sb9)Σ20S36 8.53 8.08 22.61 90.2 97.2 90.8 1546.7 P1 [14](Tl,As)-rich boscardinite AgTl3Pb4(Sb14As6)Σ20S36 8.65 8.10 22.56 90.7 97.2 90.8 1569.6 P-1 [15]Boscardinite AgTl2Pb6(Sb15As4)Σ19S36 8.76 8.09 22.50 90.9 97.2 90.8 1582.0 P-1 [16]N = 4, 3, 4 Liveingite Pb20As24S56 8.37 7.91 70.49 90.1 (AE/AR) 4669.8 P21/c [17]N = 4, 4 Dufrénoysite Pb8As8S20 8.37 7.90 25.74 90.4 (AE/AL) 1702.0 P21 [18]Veenite Pb8(Sb,As)8S20 8.42 8.96 26.2 117.4 (AE/AR) 1747.6 P21 [19]Polloneite Ag0.17Pb7.67(As4.33Sb3.83)Σ8.16S20 8.41 23.82 25.90 90.0 (AE/AL) 5189.8 P21 [20]Rathite (AgAs)Pb6As8S20 8.50 7.97 25.12 100.7 (AE/AL) 1672.2 P21/c [21]Carducciite (AgSb)Pb6(As,Sb)8S20 8.49 8.02 25.40 100.4 (AE/AL) 1701.6 P21/c [22]Barikaite* Ag0.5(AgAs)Pb5(As,Sb)8.5S20 8.53 8.08 24.95 100.7 (AE/AL) 1688.8 P21/c [23]Philrothite** Tl4As12S20 8.62 8.01 24.83 90.1 (AE/AR) 1715.9 P21/n [24]Synth. Li0.73Eu3As4.43S10 8.46 7.82 24.62 99.8 (AR/AL) 1605.0 P21/c [25]Synth. Na0.66Eu2.86As4.54S10 8.43 7.80 25.14 100.2 (AR/AL) 1626.9 P21/c [25]Synth. Ba3Sb4.667S10 8.96 8.22 26.76 100.3 (AE/AL) 1939.0 P21/c [26]Synth. Ba2.6Pb1.4Sb4S10 8.84 8.20 26.76 99.5 (AE/AL) 1914.3 P21 [26]Synth. “shift” derivative Ba2Sb2Se5 4.64 8.40 27.57 1075.3 Pbam [27]

22Orlandi et al.

618

619

4344

[1] Nowacki et al. (1961); [2] Makovicky et al. (2012); [3] Makovicky & Topa (2012); [4] Topa et al. (2015d); [5] Topa et al. (2015a); [6] Berlepsch et al. (2003); [7] Topa et al. (2015c); [8] Engel et al. (1983); [9] Engel (1980); [10] Cordier et al. (1984); [11] Cordier & Schaefer (1979); [12] Topa & Makovicky (2016a); [13] this work; [14] Topa et al. (2016); [15] Biagioni & Moëlo (2016); [16] Orlandi et al. (2012); [17] Engel & Nowacki (1970); [18] Marumo & Nowacki (1967); [19] Topa & Makovicky (2016b); [20] Topa et al. (2015b); [21] Berlepsch et al. (2002); [22] Biagioni et al. (2014); [23] Makovicky & Topa (2013); [24] Bindi et al. (2014); [25] Bera et al. (2007); [26] Choi & Kanatzidis (2000); [27] Wang et al. (2015).* Unit-cell transformed in the conventional space group P21/c though the matrix R = [1 0 0 | 0 -1 0 | -1 0 -1].** Unit-cell transformed in order to compare with dufrénoysite through the matrix R = [-1 0 0 | 0 -1 0 | 1 0 1].

23Orlandi et al.

620621622623624625626627

4546

Table 2 – Reflectance data (%) for bernarlottiite in air.

λ (nm) Rmin Rmax λ (nm) Rmin Rmax

400 30.3 - 560 30.1 37.1

420 29.4 39.6 580 29.9 36.9

440 29.9 38.3 589 29.7 36.8

460 29.8 38.1 600 29.8 36.7

470 30.0 37.5 620 29.2 35.9

480 29.9 37.6 640 29.5 36.4

500 29.9 37.2 650 29.3 36.2

520 30.2 37.4 660 28.8 35.5

540 30.4 37.5 680 28.4 36.9

546 30.3 37.3 700 28.4 36.9

Table 3 – Electron microprobe analyses of bernarlottiite: chemical composition as wt% and

chemical formula (in atoms per formula unit, apfu) on the basis of ΣMe = 28 apfu.

2987 (n = 3) 3819 (n = 5)

Element wt% range e.s.d. wt% range e.s.d.

Cu 0.09 0.00 – 0.27 0.16 0.02 0.00 – 0.07 0.03

Pb 48.89 47.48 – 49.92 1.26 47.43 47.24 – 47.88 0.26

As 17.48 17.25 – 17.68 0.22 14.56 14.31 – 14.92 0.24

Sb 11.36 11.29 – 11.47 0.10 13.92 13.69 – 14.12 0.18

S 23.11 22.85 – 23.47 0.32 22.64 22.37 – 22.81 0.17

Total 100.93 99.48 – 102.22 1.38 98.58 98.19 – 99.25 0.46

Cu 0.07 0.00 – 0.20 0.12 0.02 0.00 – 0.05 0.02

Pb 11.71 11.52 – 11.87 0.18 11.92 11.84 – 11.98 0.06

As 11.59 11.34 – 11.75 0.21 10.12 9.95 – 10.30 0.14

Sb 4.63 4.58 – 4.74 0.09 5.95 5.85 – 6.02 0.08

S 35.78 35.22 – 36.07 0.48 36.76 36.25 – 37.10 0.32

Ev* 0.8 -0.5 – 2.6 1.6 -2.0 -0.6 - -2.9 0.9

Pbcorr.** 11.85 11.52 – 12.28 0.39 11.95 11.84 – 12.08 0.09

(As+Sb)corr.** 16.15 15.72 – 16.48 0.39 16.05 15.92 – 16.16 0.09

As/(As+Sb)at. 0.71 0.71 – 0.72 0.00 0.63 0.62 – 0.64 0.01*Relative error on the valence equilibrium (%), calculated as [Σ(val+) – Σ(val-)]×100/Σ(val-). **Pbcorr. and (As+Sb)corr. on the basis of the substitution Cu+ + (As,Sb)3+ = 2Pb2+.

24Orlandi et al.

628

629

630

631

632633

4748

Table 4 –X-ray powder diffraction data for bernarlottiite. Intensities and dhkl were calculated using the software PowderCell 2.3 (Kraus and Nolze, 1996) on the basis of the structural model given in Table 4. The seven strongest reflections are given in bold. Only reflections with Icalc ≥ 10 were reported, if not observed. Observed intensities were visually estimated (s = strong; m = medium; mw = medium-weak; w = weak; vw = very weak).

Iobs dobs Icalc dcalc h k l Iobs dobs Icalc dcalc h k l

w 7.7 13 7.70 0 0 3

ms 2.823

46 2.825 -7 0 6

w 7.2 25 7.18 -2 0 3 16 2.816 -3 2 6

w 6.2 18 6.15 -3 0 3 12 2.812 -3 -2 6

w 5.8 25 5.82 2 0 3 23 2.806 -6 -2 3

w 5.17 13 5.18 -4 0 3 14 2.803 -6 2 3

w 4.91 7 4.901 3 0 3

vs 2.748

63 2.763 1 2 6

vw 4.583 9 4.581 5 0 0 63 2.756 1 -2 6

w 4.399 14 4.393 -5 0 3 56 2.728 -4 2 6

ms 4.170 57 4.170 4 0 3 58 2.725 -4 -2 6

48 4.126 1 2 0m 2.66

7

15 2.668 5 0 6

48 4.123 1 -2 0 18 2.657 2 2 6

11 4.024 5 1 0 18 2.649 2 -2 6

w 3.927 25 3.925 -2 0 6 w 2.621 11 2.61

7 -1 0 9

s 3.851 87 3.850 0 0 6w 2.56

8

6 2.567 0 0 9

s 3.79465 3.796 -3 0 6 9 2.56

7 -4 0 9

62 3.773 -6 0 3 w 2.510 13 2.50

7 8 0 3

m 3.661 49 3.665 1 0 6 vw 2.448 2 2.45

1 6 0 6

12 3.622 -2 2 3s 2.36

354 2.36

7 8 2 0

ms 3.592

60 3.599 5 0 3 55 2.362 8 -2 0

13 3.589 -4 0 6m 2.28

7

17 2.284 3 0 9

18 3.581 1 2 3 11 2.283 -7 0 9

23 3.572 1 -2 3 w 2.257 21 2.25

7 7 0 6

ms 3.44269 3.466 -3 2 3 vs 2.22

1 23 2.222 -1 2 9

72 3.465 -3 -2 3 22 2.222 -3 2 9

32 3.406 2 2 3 25 2.218 -3 -2 9

30 3.397 2 -2 3 23 2.21 -1 -2 9

25Orlandi et al.

634

635636637638639

4950

8

12 3.386 4 2 0 12 2.208 -9 -2 3

11 3.380 4 -2 0 17 2.206 -9 2 3

w 3.347 18 3.338 -5 0 6 vw 2.170 8 2.16

8 -8 0 9

13 3.288 -7 0 3 vw 2.131 4 2.13

4 -11 0 3

s 3.278

100 3.272 7 0 0 vw 2.120 4 2.11

8 6 2 6

39 3.260 -4 -2 3 m 2.087 87 2.09

6 0 4 0

41 3.260 -4 2 3ms 2.05

6

22 2.052 5 0 9

ms 3.167

59 3.191 3 2 3 14 2.051 -9 0 9

58 3.182 3 -2 3 vw 2.009 4 2.00

8 10 -2 0

33 3.165 3 0 6vw 1.96

5

4 1.962 -4 0 12

26 3.151 6 0 3 5 1.955 -1 0 12

s 3.075 75 3.077 -6 0 6

s 1.935

14 1.936 -5 0 12

ms 3.04355 3.034 -5 -2 3 13 1.92

8 4 2 9

57 3.032 -5 2 3 11 1.926 -8 2 9

m 2.95471 2.961 4 2 3 10 1.92

5 0 0 12

84 2.952 4 -2 3 13 1.924 4 -2 9

ms 2.903

36 2.908 4 0 6ms 1.86

9

17 1.869 8 2 6

28 2.904 -8 0 3 18 1.864 8 -2 6

30 2.876 -1 2 6m 1.83

3

13 1.829 -11 -2 6

21 2.870 -1 -2 6 11 1.828 -11 2 6

26Orlandi et al.

5152

Table 5 – Crystal data and summary of parameters describing data collection and refinement for bernarlottiite.

27Orlandi et al.

Crystal dataX-ray formula Pb11.93As10.00Sb6.07S36

Crystal size (mm3) 0.03 x 0.005 x 0.005Cell setting, space group Triclinic, P1

a (Å) 23.704(8)b (Å) 8.386(2)c (Å) 23.501(8)α (°) 89.91(1)β (°) 102.93(1)γ (°) 89.88(1)

V (Å3) 4553(2)Z 3Data collection and refinement

Radiation, wavelength (Å) synchrotron, λ = 0.7Temperature (K) 293

2θmax 42.30Measured reflections 10709

Unique reflections 8048Reflections with Fo > 4σ(Fo) 7317

Rint 0.0461Rσ 0.1189

Range of h, k, l24 ≤ h ≤ 24, 7 ≤ k ≤ 7, 22 ≤ l ≤ 24

R [Fo > 4σ(Fo)] 0.0885R (all data) 0.0958wR (on Fo

2) 0.2631Goof 1.095

Number of least-squares parameters 880

Maximum and minimum residual peak (e Å-3)

2.91 (at 2.07 Å from S41)-2.03 (at 1.04 Å from Pb19)

640

641642643644645

646

647

5354

Table 6 – Atomic coordinates, site occupation factors, and equivalente isotropic displacement

parameters (Å2) for bernarlottiite.

Site s.o.f. x/a y/b z/c Ueq

Pb1 Pb1.00 0.1400(1) 0.6147(4) -0.7667(1) 0.0718(8)Pb2 Pb1.00 0.1425(1) 0.1250(4) -0.7614(1) 0.0588(7)Pb3 Pb1.00 -0.5247(1) 0.6307(4) -0.7656(1) 0.0684(8)Pb4 Pb1.00 0.4774(1) 0.1274(4) -0.7692(1) 0.0594(7)Pb5 Pb1.00 0.8112(1) 0.1316(4) -0.7637(1) 0.0598(7)Pb6 Pb1.00 -0.1911(1) 0.6404(4) -0.7648(1) 0.0636(7)Pb7 Pb1.00 0.0037(1) 0.1205(4) -0.6565(1) 0.0661(8)Pb8 Pb1.00 0.0018(1) 0.3736(4) -0.3388(1) 0.0614(7)Pb9 Pb1.00 0.3307(1) 0.3763(4) -0.3435(1) 0.0585(7)

Pb10 Pb1.00 0.3334(1) -0.1266(4) -0.3416(1) 0.0592(7)Pb11 Pb1.00 0.6618(1) 0.3550(4) -0.3341(1) 0.0625(8)Pb12 Pb1.00 0.6754(1) -0.1395(4) -0.3405(1) 0.0591(7)Sb13 Sb0.75(2)Pb0.25(2) 0.0041(1) 0.1281(5) 0.0701(2) 0.059(2)Pb14 Pb1.00 0.3364(1) 0.1069(4) 0.0743(1) 0.0560(7)Pb15 Pb1.00 0.6634(1) 0.6236(4) 0.0882(1) 0.0533(6)Pb16 Pb1.00 0.9964(1) 0.6375(4) 0.0870(1) 0.0562(7)Pb17 Pb1.00 0.3258(1) 0.6172(3) 0.0815(1) 0.0532(6)Pb18 Pb0.81(2)Sb0.19(2) 0.4186(1) 0.3860(4) -0.4808(1) 0.055(1)Pb19 Pb0.51(3)Sb0.49(3) 0.0739(2) 0.3723(5) -0.4847(2) 0.075(2)As20 As0.79(4)Sb0.21(4) 0.7336(2) 0.3880(7) -0.5077(2) 0.053(2)Sb21 Sb1.00 0.3288(2) -0.1196(5) -0.0669(2) 0.048(1)As22 As0.88(4)Sb0.12(4) 0.6074(2) 0.3152(8) 0.1736(2) 0.055(2)As23 As1.00 0.9367(2) 0.3804(8) 0.1854(2) 0.045(1)As24 As1.00 0.2716(2) 0.3210(8) 0.1726(2) 0.050(2)As25 As1.00 0.6021(2) -0.1289(8) 0.1845(2) 0.049(1)As26 As1.00 0.9412(2) -0.0630(8) 0.1743(2) 0.050(2)As27 As1.00 0.2667(2) -0.1305(8) 0.1848(2) 0.050(2)As28 As0.79(4)Sb0.21(4) 0.4728(2) 0.3800(8) 0.0692(2) 0.053(2)Sb29 Sb0.68(4)As0.32(4) 0.8042(2) 0.4350(6) 0.0635(2) 0.055(2)As30 As0.84(4)Sb0.16(4) 0.1433(2) 0.3799(8) 0.0648(2) 0.053(2)Sb31 Sb1.00 0.4701(1) -0.1690(6) 0.0532(2) 0.052(1)As32 As0.73(4)Sb0.27(4) 0.8091(2) -0.1274(8) 0.0646(2) 0.054(2)Sb33 Sb0.68(2)Pb0.32(2) 0.1375(1) -0.1602(5) 0.0544(2) 0.066(2)As34 As1.00 0.5194(2) 0.6231(9) -0.3800(2) 0.049(1)As35 As1.00 0.8408(2) 0.6284(9) -0.3892(2) 0.049(2)Sb36 Sb0.71(4)As0.29(4) 0.1778(2) 0.6441(7) -0.3908(2) 0.054(2)As37 As0.77(4)Sb0.23(4) 0.5105(2) 0.0800(8) -0.3912(2) 0.053(2)Sb38 Sb1.00 0.8423(1) 0.1489(6) -0.3917(2) 0.054(2)As39 As1.00 0.1766(2) 0.1183(9) -0.3884(2) 0.048(2)As40 As0.79(4)Sb0.21(4) 0.4010(2) -0.1280(8) -0.5076(2) 0.050(2)Sb41 Sb1.00 0.7271(1) -0.1441(6) -0.4910(2) 0.049(1)As42 As0.80(4)Sb0.20(4) 0.0689(2) -0.1296(8) -0.5064(2) 0.054(2)S1 S1.00 0.6651(4) 0.674(2) 0.2097(5) 0.044(4)S2 S1.00 0.9994(4) 0.573(2) 0.2093(5) 0.034(3)S3 S1.00 0.3314(4) 0.673(2) 0.2116(5) 0.049(4)S4 S1.00 0.6628(4) 0.089(2) 0.2072(5) 0.039(3)S5 S1.00 0.9978(4) 0.157(2) 0.2104(5) 0.044(3)S6 S1.00 0.3285(4) 0.092(2) 0.2055(5) 0.037(3)S7 S1.00 0.5272(4) 0.589(2) 0.1125(5) 0.042(3)S8 S1.00 0.8634(4) 0.662(2) 0.1164(5) 0.042(3)S9 S1.00 0.1956(5) 0.582(2) 0.1136(6) 0.050(4)

S10 S1.00 0.5339(5) 0.174(2) 0.1172(6) 0.046(3)S11 S1.00 0.8692(5) 0.076(2) 0.1171(6) 0.050(4)S12 S1.00 0.2008(5) 0.177(2) 0.1151(6) 0.054(4)S13 S1.00 0.7538(4) 0.394(2) 0.1387(6) 0.047(3)S14 S1.00 0.0775(4) 0.370(2) 0.1226(6) 0.044(3)

28Orlandi et al.

648

649

5556

S15 S1.00 0.4112(5) 0.364(2) 0.1298(6) 0.047(3)S16 S1.00 0.7448(4) -0.120(2) 0.1262(5) 0.045(3)S17 S1.00 0.0828(4) -0.137(2) 0.1349(5) 0.042(3)S18 S1.00 0.4180(4) -0.126(2) 0.1298(5) 0.043(3)S19 S1.00 0.6017(4) 0.355(2) 0.0027(5) 0.046(3)S20 S1.00 0.9379(5) 0.352(2) 0.0070(5) 0.046(3)S21 S1.00 0.2642(5) 0.389(2) -0.0013(5) 0.042(3)S22 S1.00 0.6048(5) -0.091(2) 0.0143(6) 0.043(3)S23 S1.00 0.9335(5) -0.102(2) 0.0030(6) 0.042(3)S24 S1.00 0.2643(4) -0.139(2) 0.0000(5) 0.041(3)S25 S1.00 0.4296(4) 0.638(2) -0.2520(5) 0.037(3)S26 S1.00 0.7626(4) 0.641(2) -0.2533(5) 0.042(3)S27 S1.00 0.1012(4) 0.619(2) -0.2647(5) 0.038(3)S28 S1.00 0.4363(4) 0.129(2) -0.2633(5) 0.038(3)S29 S1.00 0.7715(5) 0.130(2) -0.2624(5) 0.046(3)S30 S1.00 0.0967(4) 0.112(2) -0.2521(5) 0.039(3)S31 S1.00 0.5960(5) 0.621(2) -0.3041(6) 0.046(3)S32 S1.00 0.9202(5) 0.630(2) -0.3169(5) 0.047(3)S33 S1.00 0.2511(5) 0.628(2) -0.3029(5) 0.045(3)S34 S1.00 0.5814(5) 0.112(2) -0.3093(5) 0.043(3)S35 S1.00 0.9184(5) 0.133(2) -0.3036(6) 0.048(3)S36 S1.00 0.2546(5) 0.117(2) -0.3158(5) 0.044(3)S37 S1.00 0.4687(5) 0.427(2) -0.3504(5) 0.042(3)S38 S1.00 0.7978(5) 0.418(2) -0.3531(5) 0.043(3)S39 S1.00 0.1313(5) 0.325(2) -0.3560(5) 0.045(3)S40 S1.00 0.4700(5) -0.157(2) -0.3567(5) 0.040(3)S41 S1.00 0.7991(4) -0.154(2) -0.3572(5) 0.040(3)S42 S1.00 0.1325(4) -0.103(2) -0.3582(6) 0.042(3)S43 S1.00 0.3555(4) -0.381(2) -0.4339(5) 0.038(3)S44 S1.00 0.6842(4) -0.351(2) -0.4379(5) 0.036(3)S45 S1.00 0.0223(5) -0.397(2) -0.4306(5) 0.047(4)S46 S1.00 0.3576(4) 0.136(2) -0.4270(5) 0.035(3)S47 S1.00 0.6906(5) 0.104(2) -0.4389(5) 0.040(3)S48 S1.00 0.0215(4) 0.135(2) -0.4369(5) 0.036(3)S49 S1.00 0.5677(4) 0.334(2) -0.4449(5) 0.037(3)S50 S1.00 0.8960(5) 0.337(2) -0.4451(6) 0.046(3)S51 S1.00 0.2303(5) 0.410(2) -0.4447(5) 0.038(3)S52 S1.00 0.5606(5) -0.082(2) -0.4434(5) 0.040(3)S53 S1.00 0.8967(5) -0.070(2) -0.4438(5) 0.041(3)S54 S1.00 0.2310(5) -0.176(2) -0.4450(5) 0.041(3)

29Orlandi et al.

650

5758

Table 7 – Average bond-distances (in Å) and bond-valence sums (in valence units) for metal sites

in bernarlottiite.

Site <Me–S> BVS Site <Me–S> BVS Site <Me–S> BVS

Pb1 3.191 1.78 Pb15 3.045 2.03 Sb29 2.438 2.93

Pb2 3.211 1.87 Pb16 3.044 2.02 As30 2.291 3.25

Pb3 3.204 1.85 Pb17 3.034 2.03 Sb31 2.515 2.94

Pb4 3.188 1.84 Pb18 3.040 2.08 As32 2.356 3.09

Pb5 3.201 1.87 Pb19 2.918 2.28 Sb33 2.947 2.59

Pb6 3.186 1.80 As20 2.297 3.33 As34 2.266 3.12

Pb7 3.203 1.74 Sb21 2.468 2.90 As35 2.270 3.08

Pb8 3.161 1.84 As22 2.285 3.21 Sb36 2.489 2.97

Pb9 3.186 1.84 As23 2.262 3.20 As37 2.341 3.07

Pb10 3.189 1.75 As24 2.290 3.00 Sb38 2.549 3.14

Pb11 3.232 1.88 As25 2.257 3.19 As39 2.268 3.11

Pb12 3.164 1.84 As26 2.276 3.05 As40 2.308 3.25

Sb13 2.863 2.65 As27 2.265 3.14 Sb41 2.530 2.93

Pb14 2.973 2.08 As28 2.301 3.16 As42 2.293 3.32

Note: for pure As, pure Sb, and mixed (Sb/As) sites, <Me–S> distances are calculated taking into account

Me–S distances shorter than 2.70 Å.

30Orlandi et al.

651

652

653

654

655

5960

Table 8 – Metal site distribution within the crystal structure of bernarlottiite. Sc and Sa represent the

centric and acentric ribbons in the N = 3 layer, respectively; Dc and Da represent the centric and

acentric ribbons in the N = 4 layers.

N = 3 N = 4Position number

Metal site Sc Sa (× 2) Dc Da (× 2)

Pb

(interlayer)4 4 4 4 12

Pb

(intralayer)0 0 2 2 4

(Pb/Sb) 2 (0.51/0.49) 0.81/0.19 0 0 2

(Sb/Pb) 0 02 (0.68/0.32)

2 (0.75/0.25)0 2

Sb 2 1 0 2 4

(Sb/As) 0 0.71/0.29 0 0.68/0.32 2

(As/Sb) 2 (0.80/0.20)0.77/0.23

0.79/0.21 (× 2)2 (0.84/0.16)

0.73/0.27

0.79/0.21

0.88/0.12

8

As 2 2 4 4 8

Total/Ribbon

Centric Pb5.02Sb3.38As3.60S16 Pb7.14Sb3.18As5.68S20

Acentric (× 2) Pb4.81Sb2.55As4.64S16 Pb7.00Sb3.28As5.72S20

Mean Pb4.88(Sb2.83As4.29)Σ7.12S16 Pb7.05(Sb3.25As5.71)Σ8.96S20

Simplified Pb5(Sb3As4)Σ7S16 Pb7(Sb3As6)Σ9S20

Ideal Pb4As8S16 (sartorite) Pb8As8S20 (dufrénoysite)

Total/Layer (Pb14.64Sb8.48As12.88S48)-2.64 (Pb21.14Sb9.74As17.12S60)+2.86

Formula unit

(Z = 3)Pb11.93(Sb6.07As10.00)Σ16.07S36

Note: in the upper part, integers correspond to number of atom positions, whereas non-integer values to site occupancy factors in mixed positions.

31Orlandi et al.

656

657

658

659660661

6162

Figure 1 – Bernarlottiite, black acicular crystals. Ceragiola area, Seravezza, Apuan Alps, Tuscany,

Italy. Collection Museo di Storia Naturale, Università di Pisa. Catalogue number 19687.

32Orlandi et al.

662

663

664

6364

Figure 2 – Reflectance spectra of bernarlottiite. For sake of comparison, the reflectance spectra of

its Tl-Sb homeotype boscardinite (Orlandi et al., 2012) a shown.

33Orlandi et al.

665

666

667

6566

Figure 3 – Unit-cell content of bernarlottiite, as seen down b.

34Orlandi et al.

668

669

670

6768

Figure 4 – General organization of bernarlottiite, as seen down b. Dotted and dashed lines delimit

the N =3 and N = 4 ribbons, respectively. Red and blue lines indicate the centrosymmetric and

acentric ribbons, respectively.

35Orlandi et al.

671

672

673

674

6970

Figure 5 – Polymeric organization of (Sb/As) atoms with S atoms (short bonds, thick dark green

lines) in the sartorite type layer. The two ribbons Sc (left) and Sa (right) are shown. Thick tie-lines

correspond to longer bonds, related to mean Sb positions, or mixed (Pb,Sb) sites. In Sc ribbon (left),

the lower part indicates the two possible polymer combinations (separated by red tie-line),

according to the “up” or “down” positions of Sb atoms.

36Orlandi et al.

675

676

677

678

679

680

7172

Figure 6 – Polymeric organization of (Sb/As) atoms with S atoms (short bonds, thick dark green

lines) in the dufrénoysite type layer. The two ribbons Dc (left) and Da (right) are shown

37Orlandi et al.

681

682

683

684

7374