Mineralogical Magazine, December 2014, Vol. 78(7), pp. 1775–1793

Lead-antimony sulfosalts from Tuscany (Italy). XVI.
Carducciite, (AgSb)Pb6(As,Sb)8S20, a new Sb-rich
derivative of rathite from the Pollone mine, Valdicastello
Carducci: occurrence and crystal structure
CRISTIAN BIAGIONI1,*, PAOLO ORLANDI1, YVES MOËLO2 AND LUCA BINDI3
1

Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, I-56126 Pisa, Italy
Institut des Matériaux Jean Rouxel, UMR 6502, CNRS, Université de Nantes, 2, rue de la Houssinière,44 322 Nantes Cedex 3, France
3
Dipartimento di Scienze della Terra, Università di Firenze, Via G. La Pira 4, I-50121 Florence, Italy
2[Received 21 January 2014; Accepted 25 June 2014; Associate Editor: A. Pring]
ABSTRACTThe new mineral species carducciite, (AgSb)Pb6(As,Sb)8S20, has been discovered in the baryte-pyrite(Pb-Ag-Zn) deposit of the Pollone mine, near Valdicastello Carducci, Apuan Alps, Tuscany, Italy. It
occurs as black metallic prismatic crystals, up to 0.5 mm long, associated with pyrite and sterryite. Its
Vickers hardness (VHN10) is 61 kg/mm2 (range: 52 66), corresponding to a Mohs hardness of ~2 3.
In reﬂected light, carducciite is dark grey in colour, moderately bireﬂectant; internal reﬂections arevery weak and deep red in colour. Reﬂectance percentages for the four COM wavelengths [Rmin, Rmax(%) (l)] are: 35.8, 40.8 (471.1 nm), 33.7, 39.0 (548.3 nm), 32.7, 37.6 (586.6 nm) and 30.4, 35.1
(652.3 nm). Electron microprobe analysis gives (wt.%mean of six analyses): Ag 3.55(12), Tl
0.13(3), Pb 41.90(42), Sb 17.79(19), As 12.41(14), S 22.10(17), total 97.9(6). On the basis of SMe =16 a.p.f.u., the chemical formula is Ag0.96Tl0.02Pb5.91As4.84Sb4.27S20.14. The main diffraction lines,
corresponding to multiple hkl indices, are (relative visual intensity): 3.689 (s), 3.416 (s), 3.125 (s),2.989 (s), 2.894 (s), 2.753 (vs), 2.250 (s). The crystal-structure study gives a monoclinic unit cell, spacegroup P21/c, with a 8.4909(3), b 8.0227(3), c 25.3957(9) Å, b 100.382(2)º, V 1701.63(11) Å3, Z = 2.
The crystal structure has been solved and reﬁned to a ﬁnal R1 = 0.063 on the basis of 4137 observed
reﬂections. It can be described within the framework of the sartorite homologous series, as formed bychemically twinned layers of the dufrénoysite type. The simpliﬁed idealized structural formula, basedon 20 sulfur atoms, can ideally be written as (AgSb)Pb6(As,Sb)S=8S20. Carducciite is an (Ag,Sb)-rich
homeotype of dufrénoysite, stabilized by the complete coupled substitution 2 Pb2+ = Ag+ + Sb3+ on a
speciﬁc site of the crystal structure. Together with barikaite, it belongs to the rathite sub-group of P21/chomeotypes of dufrénoysite, of which the crystal chemistry is discussed. The distribution of Ag,
coupled with As or Sb on speciﬁc sites, appears to be the main criterion for the distinction between thethree species of this sub-group.
K EY WORDS : carducciite, new mineral, rathite, sulfosalt, lead, silver, antimony, arsenic, crystal structure,
Pollone mine, Apuan Alps, Tuscany, Italy.

* E-mail: biagioni@dst.unipi.it
DOI: 10.1180/minmag.2014.078.7.19# 2014 The Mineralogical Society

Introduction
DURING the last ﬁve years, a series of new or veryrare Ag-Pb/Sb-As and Tl-Pb/Sb-As sulfosalts has
been identiﬁed from the baryte-pyrite-iron oxide

CRISTIAN BIAGIONI ET AL.

deposits of the southern Apuan Alps, Tuscany,
Italy: sterryite, parasterryite and meerschautite fromthe Pollone mine, near Valdicastello Carducci(Moëlo et al., 2011; Biagioni et al., 2013a); andboscardinite and protochabournéite from the Monte
Arsiccio mine (Orlandi et al., 2012, 2013).
During a routine check of mineral samples fromthe Pollone mine, some crystals were initially
identiﬁed as an Sb-rich variety of rathite (Biagioni
et al., 2012). Rathite is a very rare Ag-(Tl)-Pb
sulfosalt ﬁrst described by Baumhauer (1896) from
Lengenbach, Binntal, Switzerland. Recently, rathite
was also identiﬁed from the dolostone outcrop of
Reckibach, Binntal, Switzerland (Cannon et al.,2008). Consequently, Pollone mine could be thethird natural occurrence of this sulfosalt that isdeserving of a more accurate characterization. In
addition, preliminary chemical analysis showed an
unusual richness in antimony, a surprising feature
given that rathite from Lengenbach shows only
minor Sb. Therefore, a crystallographic study has
been undertaken, which shows the peculiar crystalchemical role played by Sb.
Crystallographic study, chemical analysis andcrystal-chemical considerations point to the
distinction between rathite and this Sb-rich
derivative, which has been named carducciite.
The mineral and its name have been approved by
the CNMNC-IMA, under the number 2013-006(Biagioni et al., 2013b). The holotype specimenof carducciite is deposited in the mineralogicalcollection of the Museo di Storia Naturale,
Università di Pisa, Via Roma 79, Calci, Pisa,
Italy, under catalogue number 19646. The name isfor the type locality, Valdicastello Carducci. Thisis the type locality of two other sulfosalts,
parasterryite (Moëlo et al., 2011) and meerschautite (Biagioni et al., 2013a). The name also
remembers the family name Carducci: the Italianpoet Giosué Carducci (1835 1907), Nobel Prizewinner for literature in 1906, was born at
Valdicastello. His father, Michele (1808 1858),
was employed as a doctor at the Pollone Pb-Ag
mine from 1833 to 1836.
After the submission of the approval proposalof carducciite to the CNMNC-IMA, we becameaware of the approval of barikaite (IMA 2012055; Topa et al., 2013), a closely related but
distinct phase, found in the Barika Au-Ag deposit,
Azarbaijan Province, western Iran. In this paper
we describe carducciite from the baryte-pyrite(Pb-Zn-Ag) deposit of Pollone, Valdicastello
Carducci, and discuss its crystal-chemical relationship with rathite and barikaite.

Geological setting
The baryte-pyrite-(Pb-Ag-Zn) deposit of Pollone(43º57’N; 10º16’E) is located in the southern
portion of the Sant’Anna tectonic window, an area
in which metamorphic rocks are surrounded by
the non-metamorphic sedimentary formations of
the Tuscan Nappe. The deposit is hosted in the
Scisti di Fornovolasco Formation, belonging to
the Fornovolasco-Panie Unit. This formation isrelated to the Variscan basement of the Apuan
Unit (Pandeli et al., 2004) and consists of a
Palaeozoic to Early Triassic(?) metavolcanicmetasedimentary sequence metamorphosed togreenschist facies. During the late stages of the
Alpine orogeny, the development of shear zones
led to the formation of numerous quartz + baryte
veins; ﬂuids were focused along these shear zones
giving rise to syn-metamorphic and syn-tectonic
veins. Estimates of P T conditions indicate thathost and country rocks record metamorphic
temperatures and pressures of ~350ºC and
0.35 GPa, respectively; appreciably higher
temperatures (~450ºC) were found for themineralizing ﬂuids (Costagliola et al., 1998).
A great variety of sulfosalts have been
described from all the baryte-pyrite-iron oxide
deposits from the southern Apuan Alps (Table 1),
and in particular from the Buca della Vena, Monte
Arsiccio and Pollone mines. It is interesting tonote that every deposit has some chemical
peculiarities. Indeed, Buca della Vena mine ischaracterized by the occurrence of oxy-sulfosalts
and oxy-chloro-sulfosalts; the Monte Arsiccio
mine is particularly attractive for the occurrenceof thallium sulfosalts, and the Pollone mine shows
the presence of complex silver-lead sulfosalts.
Carducciite is one of these rare mineral species.
Occurrence and mineral description
Physical and optical properties
Carducciite has been identiﬁed in only a few
specimens from the Pizzone stope, in an area richin acicular sulfosalts. It was observed embedded
in saccharoidal baryte or rarely in small vugs, as
black prismatic crystals, striated parallel to theelongation, up to 0.5 mm long and 0.2 mm wide
(Fig. 1). It is brittle, with a conchoidal fracture.
The streak is black and the lustre is metallic.
Micro-indentation measurements carried out
with a VHN load of 10 g give a mean value of
61 kg/mm2 (range: 52 66) corresponding to a
Mohs hardness of ~2 3.

1776

CARDUCCIITE FROM TUSCANYTABLE 1. Lead sulfosalts from baryte-pyrite-iron oxide deposits from the southern Apuan Alps. Abbreviations
for localities: BdV = Buca della Vena mine; Fv = Fornovolasco mine; MA = Monte Arsiccio mine; Pl =Pollone mine.
Chemical formula

Localities

Lead sulfosalts
Boulangerite
Geocronite
Jordanite
Robinsonite
Twinnite
Zinkenite

Pb5Sb4S11
Pb14Sb6S23
Pb14As6S23
Pb4Sb6S13
Pb(Sb0.63As0.37)2S4
Pb9Sb22S42

BdV, Fv, MA, PlPlPl
BdV, MA
MA, Pl
BdV, MA, Pl

Lead-copper sulfosalts
Bournonite
Jaskólskı́ite
Meneghinite
Tintinaite

CuPbSbS3
CuxPb2+x(Sb,Bi)2-xS6
CuPb13Sb7S24
Cu2Pb10Sb16S35

BdV, Fv, Pl
Fv
Fv, Pl
BdV

Lead-iron sulfosalts
Jamesonite

FePb4Sb6S14

Fv

Lead-mercury and lead-copper-mercury sulfosalts
Marrucciite{
Hg3Pb16Sb18S46
Rouxelite{
Cu2HgPb23Sb27S65.5

BdV
BdV, MA

Lead-silver sulfosalts
Carducciite*{
Diaphorite
Meerschautite*{Owyheeite
Parasterryite*{
Sterryite*(AgSb)Pb6(As,Sb)8S20
Ag3Pb2Sb3S8(Ag,Cu)6Pb43 2xSb44+2xS112Ox (x ~ 0.5)
Ag3Pb10Sb11S28
Ag4Pb20(Sb,As)24S58
Cu(Ag,Cu)3Pb19(Sb,As)22(As-As)S56

Pl
Pl
Pl
Pl
Pl
Pl

Lead-thallium sulfosalts
Boscardinite*{
Protochabournéite*{

TlPb4(Sb7As2)S9S18
Tl2Pb(Sb9-8As1-2)S10S17

MA
MA

Lead oxysulfosalts, chlorosulfosalts and oxy-chlorosulfosalts
Dadsonite
Pb23Sb25S60Cl
Pellouxite{(Cu,Ag)2Pb21Sb23S55ClO
Pillaite{
Pb9Sb10S23ClO0.5
Scainiite{
Pb14Sb30S54O5

BdV
BdV
BdV
BdV

Notes: chemical formulae are from Moëlo et al. (2008), with the exception of sulfosalt species denoted with *, where
the chemical formulae are after Moëlo et al. (2012) [parasterryite and sterryite], Orlandi et al. (2012) [boscardinite],
Orlandi et al. (2013) [protochabournéite], Biagioni et al. (2013a) [meerschautite] and this work [carducciite].
The symbol { indicates sulfosalts described for the ﬁrst time from the baryte-pyrite-iron oxides of Apuan Alps.

In plane-polarized incident light, carducciite isdark grey in colour, moderately bireﬂectant andpleochroic from light grey to a slightly greenish
grey. Between crossed polars, carducciite is
anisotropic with greyish to light-blue rotation
tints. Internal reﬂections are very weak and deep
red in colour. There is no optical evidence ofgrowth zonation.
1777

Reﬂectance measurements were performed in
air by means of a MPM-200 Zeiss microphotometer equipped with a MSP-20 system processor
on a Zeiss Axioplan ore microscope. The ﬁlament
temperature was ~3350 K. An interference ﬁlter
was adjusted, in turn, to select four COM (IMA
Commission on Ore Microscopy) wavelengths formeasurement (471.1, 548.3, 586.6 and 652.3 nm).

CRISTIAN BIAGIONI ET AL.

size 5 mm. Standards (element, emission line,
counting times for one spot analysis) are: pyrite(SKa, 20 s), stibnite (SbLa, 20 s), AsGa (AsLa,
30 s), Ag metal (AgLa, 20 s), galena (PbMa, 20 s)
and lorándite (TlMa, 20 s).
Electron microprobe data for carducciite are
given in Table 2. Notwithstanding the low total,probably due to the poor quality of the polishedsurface, the results are in agreement with thestructural analysis (see below). On the basis of
SMe = 16 atoms per formula unit (a.p.f.u.), thechemical formula can be written as
Ag0.96(3)Tl0.02(1)Pb5.91(4)(As4.84(4)Sb4.27(5))S=9.11
S20.14(15). If Tl and Ag are subtracted according to
the substitution rule (Tl, Ag)+ + (As, Sb)3+ =2 Pb2+, the chemical formula can be written
Pb7.87(As,Sb)S=8.13S20.14(14), agreeing with thegeneral formula of the N = 4 dufrénoysite
homologue of the sartorite series (Makovicky,1985), Pb8As8S20.
Crystallography
FIG. 1. Carducciite, black prismatic crystals up to
0.5 mm. The conchoidal fracture of carducciite isclearly visible.

Readings were taken for specimen and standard(SiC) maintained under the same focus conditions. The diameter of the circular measuring area
was 0.1 mm. Reﬂectance percentages for Rmin andRmax (%) are 35.8, 40.8 (471.1 nm), 33.7, 39.0
(548.3 nm), 32.7, 37.6 (586.6 nm) and 30.4, 35.1
(652.3 nm), respectively.
Owing to its softness and fragility, only minutegrains could be extracted from baryte for X-ray
study and preparation as polished sections for
microprobe analysis and reﬂectance measurement. These grains were unsuitable for measuring
the density. Calculated density (based on theempirical formula) is 5.56 g/cm3.
Carducciite is associated with baryte, pyrite,
sphalerite, sterryite and twinnite. Up to now, only
a few sub-millimeter-sized fragments of carducciite have been identiﬁed; it is probably the rarest
sulfosalt found so far at the Pollone mine.
Chemical analysis
A crystal of carducciite was analysed with a
CAMEBAX SX50 electron microprobe (BRGMCNRS-University common laboratory, Orléans,
France). The operating conditions were: accelerating voltage 20 kV, beam current 20 nA, beam
1778

The powder X-ray diffraction pattern of carducciite was obtained using a 114.6 mm diameter
Gandolﬁ camera, with Ni-ﬁltered CuKa radiation.
The observed powder X-ray diffraction pattern iscompared with the calculated one (obtained using
the software PowderCell; Kraus and Nolze, 1996)
in Table 3. Unit-cell parameters were not reﬁned
from the powder X-ray diffraction data because of
the multiplicity of indices for the majority of thediffraction lines.
For the single-crystal X-ray diffraction study,
the intensity data were collected using a Bruker
Smart Breeze diffractometer equipped with an aircooled CCD detector, with MoKa radiation. The
detector to crystal distance was 50 mm. 878
frames were collected using o scan mode, in 0.5º
slices, with an exposure time of 10 s per frame.
The data were corrected for Lorentz andpolarization factors and absorption using thesoftware package Apex2 (Bruker AXS Inc.,
2004). The statistical tests on the distribution of|E| values (|E2 1| = 0.868) and the systematicabsences suggested the space group P21/n, which
was subsequently transformed by the matrix R =(1 0 0, 0 1̄ 0, 1̄ 0 1̄) into the standard setting P21/c.
The reﬁned cell parameters, in the standard
setting, are a 8.4909(3), b 8.0227(3),c 25.3957(9) Å, b 100.382(2)º, V 1701.63(11) Å3.
The crystal structure was reﬁned using
SHELXL-97 (Sheldrick, 2008) starting from theatomic coordinates given by Berlepsch et al.

CARDUCCIITE FROM TUSCANYTABLE 2. Microprobe analysis of carducciite: chemical composition as wt.% and chemical
formula (in atoms per formula unit, a.p.f.u.) on the basis of SMe = 16 a.p.f.u.
Element

Range

Mean (n = 6)

e.s.d.

Ag
Tl
Pb
Sb
As
S
Total

3.33
0.11
41.55
17.56
12.27
21.96
97.53

3.66
0.18
42.62
18.13
12.59
22.37
99.08

3.55
0.13
41.90
17.79
12.41
22.10
97.87

0.12
0.03
0.42
0.19
0.14
0.17
0.61

Ag
Tl
Pb
Sb
As
S
Ev*
Pbcorr.**(Sb +As)corr.**
Sb/(Sb +As)at.

0.905 0.990
0.015 0.025
5.975 5.870
4.225 4.360
4.795 4.890
19.940 20.410
1.4 0.1
5.900 6.015
9.070 9.140
0.464 0.476

0.961
0.018
5.910
4.270
4.841
20.143
0.4
5.947
9.093
0.469

0.031
0.004
0.041
0.052
0.035
0.147
0.7
0.043
0.025
0.005

* Relative error on the valence equilibrium (%), calculated as [S(val+) S(val )]6100 / S(val ).
** Pbcorr. and (Sb+As)corr. on the basis of the substitution Tl+ + (As,Sb)3+ = 2 Pb2+.

(2002). Scattering curves for neutral atoms weretaken from the International Tables for
Crystallography (Wilson, 1992). Crystal data
and details of the intensity data collection andreﬁnement are reported in Table 4. After several
cycles of isotropic reﬁnement, the R1 converged
to 0.14; by reﬁning the anisotropic displacement
parameters for the metals only, the reﬁnement
yielded an R1 value of 0.074, thus conﬁrming thecorrectness of the structural model. Successive
cycles of reﬁnement converged to R1 = 0.071,
with an anisotropic model for all the atoms. The
M5 site was found to split in two positions (i.e.
M5a and M5b). The reﬁnement of the occupancy
factors at these sites (using Sb vs. structural
vacancy) led to 24.7 and 24.2 electrons,
respectively. Examination of bond distancessuggests that M5a is occupied by the larger
cation Ag, whereas M5b is occupied by Sb. The
successive reﬁnement cycles were carried out
using Ag vs. vacancy (M5a) and Sb vs. vacancy(M5b) which lowers the R1 to 0.069, and gave an
overall composition for the M5 site of
Ag0.53Sb0.47, in good agreement with the expectedvalue. Finally, the occupancies were reﬁned for
M2, M3, M4 (As vs. Sb) and M6 (Pb vs. As).
1779

According to Marumo and Nowacki (1965),
rathite (‘‘rathite I’’ of these authors), homeotypicwith carducciite (see below), is usually polysynthetically twinned. To verify such pseudomerohedral twinning, the twin law (1̄ 0 0, 0 1̄ 0,
1 0 1) was added in the reﬁnement but noimprovement was found, thus indicating that the
crystal s tudied is actually untwinned.
Notwithstanding the observation of Marumo andNowacki (1965), Berlepsch et al. (2002), throughsingle-crystal X-ray diffraction data, Pring (2001),
through high-resolution transmission electron
microscopy and Topa et al. (2013), throughreﬂected light microscopy, observed no twinningin rathite and barikaite, respectively.
The reﬁnement ﬁnally converged to R1 =0.063 for 4137 reﬂections with Fo > 4s(Fo) and
0.103 for all 6078 independent reﬂections. The
highest and deepest residuals are located aroundthe Pb2 site. Atomic coordinates and bonddistances are reported in Table 5 and Table 6,
respectively, and the unit-cell content with atomlabels is given in Fig. 2. Bond-valence sums are
given in Table 7.
The crystal-chemical formula of carducciite, as
obtained through this reﬁnement of the crystal

CRISTIAN BIAGIONI ET AL.

TABLE 3. Powder X-ray diffraction data for carducciite.
Iobs

dmeas

mw
mw
mw
w
mw

7.6
6.8
5.79
5.42
4.92

m

4.21

m

4.01

ms

3.815

s

3.689

{
{
{

ms

3.592

{

s

3.416

{

vw

3.241

s

{
3.125 {
2.989 {

s

2.894

{

mw

2.833

{

w

2.798

vs

2.753

m
s

3.221

{

ms

2.657

{

mw

2.632

{

vw
vw

2.462
2.388

Icalc

dcalc

h k l

Iobs

dmeas

Icalc

dcalc

h k l

6
17
16
15
9
19
21
38
17
17
23
8
78
6
100
11
20
30
36
70
69
8
5
25
23
67
45
60
93
21
29
13
9
62
13
15
17
20
99
85
15
7
12
16
8
9
14
6
9

12.49
7.64
6.75
5.78
5.50
4.93
4.24
4.19
4.18
4.03
4.01
3.961
3.819
3.802
3.695
3.619
3.614
3.605
3.582
3.436
3.406
3.375
3.256
3.233
3.200
3.128
3.122
3.017
2.984
2.916
2.910
2.899
2.893
2.889
2.845
2.834
2.804
2.771
2.760
2.744
2.666
2.663
2.659
2.651
2.633
2.630
2.615
2.458
2.385

0 0 2
0 1 1
0 1 2
0 1 3
1̄ 0 40 1 4
0 1 5
2̄ 0 22 0 0
1̄ 0 6
0 2 0
0 2 1
0 2 2
2̄ 0 40 1 6
1̄ 2 10 2 3
2̄ 1 32 1 1
2̄ 1 42 1 2
0 2 4
2̄ 0 62̄ 1 5
2 1 3
0 2 5
0 0 8
2̄ 1 62 1 4
2̄ 2 11̄ 1 82̄ 2 22 2 0
0 2 6
2̄ 2 32 2 1
2̄ 1 72 1 5
2̄ 2 42 2 2
0 2 7
3̄ 1 10 3 1
2̄ 2 5
2 2 3
3 1 0
0 3 2
0 3 4
0 1 10

m

2.337

m

2.311

{

s

2.250

{

vw
vw

2.220
2.182

w

2.12

w
w

2.067
2.032

w

1.983

vw
vw

1.951
1.925

mw

1.912

vw

1.883

w

1.846

{

mw

1.833

{

w

1.810

{

m

1.796

{

m

1.744

{

mw
mw
w

1.706
1.661
1.575

mw

1.557

50
7
43
9
25
22
21
11
10
5
65
8
8
18
6
11
7
9
13
13
16
5
6
10
12
9
7
8
7
9
10
7
10
14
8
12
17
6
9
6
10
16
9
7
7
17
5
5

2.337
2.314
2.309
2.282
2.254
2.252
2.250
2.244
2.219
2.185
2.122
2.120
2.068
2.031
2.019
1.980
1.957
1.950
1.926
1.917
1.905
1.880
1.858
1.852
1.850
1.848
1.838
1.831
1.829
1.826
1.811
1.809
1.808
1.800
1.796
1.793
1.784
1.763
1.749
1.746
1.745
1.742
1.703
1.659
1.564
1.554
1.550
1.503

2̄ 0 10
1 3 4
2 0 8
0 2 9
2̄ 3 22 3 0
0 3 6
2̄ 1 102 1 8
0 1 114̄ 0 20 2 102 1 9
0 3 8
2̄ 2 100 4 2
4̄ 1 60 4 3
0 3 9
2̄ 3 82 3 6
3̄ 3 54̄ 2 44 2 0
4̄ 1 80 2 122̄ 3 94 1 4
2̄ 1 132 3 7
2 1 112̄ 4 22 4 0
2̄ 2 122̄ 4 32 4 1
2 2 104̄ 2 74 2 3
3̄ 2 114 0 6
0 1 144 2 4
2 4 5
0 4 10
0 5 4
4̄ 3 80 4 11{{{

Notes: the dhkl values were calculated on the basis of the unit cell reﬁned by using single-crystal data. Intensities
were calculated on the basis of the structural model. Observed intensities were estimated visually. vs = very strong;s = strong; ms = medium-strong; m = medium; mw = medium-weak; w = weak; vw = very weak. Only reﬂections
with Icalc > 5 are listed, if not observed. The seven strongest reﬂections are shown in bold.

1780

CARDUCCIITE FROM TUSCANYTABLE 4. Crystal data and summary of parameters describing data collection and reﬁnement for carducciite.
Crystal data
X-ray formula
Crystal size (mm)Cell setting, space groupa, b, c (Å);
a, b, g (º)
V (Å3)Z, Dc (g/cm3)

Ag1.05Pb5.84As4.63Sb4.48S20
0.2760.1660.16
Monoclinic, P21/c
8.4909(3), 8.0227(3), 25.3957(9);90.00, 100.382(2), 90.00
1701.63(11)2, 5.576

Data collection and refinement
Radiation, wavelength (Å)
Temperature (K)Maximum observed 2y (º)
Measured reflections
Unique reflections
Reflections Fo > 4s(Fo)Rint after absorption correction
Rs
Range of h, k, l
R [Fo>4 s Fo]
R (all data)wR (on F2o)
Gof
Number of least-squares parameters
Maximum and minum residual peak (e/Å3)

MoKa, l = 0.71073
293
65.14
17,4096078
4137
0.05330.0691
12 4 h 4 12, 12 4 k 4 10,
0.06300.10260.14601.107
174
6.10 (at 0.74 Å from Pb2)
6.96 (at 0.77 Å from Pb2)

33 4 l 4 38

TABLE 5. Atomic positions and equivalent displacement parameters for carducciite.
Site

Occupancy

x/a

y/b

z/c

Ueq (Å2)

Pb1
Pb2
M1
M2
M3
M4
M5a
M5b
M6a
M6b
S1
S2
S3
S4
S5
S6
S7
S8
S9
S10

Pb1.00Pb1.00As0.98(1)Sb0.02(1)As0.60(1)Sb0.40(1)Sb1.00As0.66(1)Sb0.34(1)Ag0.526(4)Sb0.474(4)Pb0.920(5)As0.080(5)
S1.00
S1.00
S1.00
S1.00
S1.00
S1.00
S1.00
S1.00
S1.00
S1.00

0.47837(7)0.97620(8)0.29523(14)0.24213(17)0.67428(11)0.13884(14)0.4176(5)0.4164(5)0.90744(8)0.898(3)0.2596(4)0.2509(4)0.5000(4)0.9128(4)0.6880(4)0.1733(4)0.3756(4)0.9587(4)0.5942(4)0.1652(4)0.73364(7)0.73021(10)0.83027(17)0.31010(15)0.63675(12)0.65000(17)0.0193(6)0.0316(6)0.07271(12)0.013(4)0.9911(4)0.4623(4)0.6612(4)0.1581(4)0.8348(4)0.8692(4)0.5061(4)0.4983(4)0.2000(5)0.1876(5)0.20441(2)0.20198(3)0.34013(5)0.14809(5)0.04195(4)0.05807(6)0.0746(2)0.0541(2)0.07400(3)0.085(1)0.2658(1)0.2257(1)0.3214(1)0.1830(1)0.1153(1)0.1191(1)0.1013(1)0.0977(1)0.0098(2)0.0075(1)0.0330(2)0.0503(2)0.0198(4)0.0303(4)0.0288(2)0.0314(4)0.0332(5)0.0332(5)0.0302(3)0.0302(3)0.0227(6)0.0207(5)0.0223(6)0.0217(6)0.0230(6)0.0247(6)0.0226(6)0.0248(7)0.0306(8)0.0267(7)1781

CRISTIAN BIAGIONI ET AL.

TABLE 6. Selected bond distances (Å) in carducciite.
Pb1

S1
S3
S2
S7
S2
S5
S6
S1
S3

2.950(3)2.999(3)3.023(3)3.183(4)3.214(3)3.226(3)3.250(3)3.344(3)3.503(3)

Pb2

S4
S1
S5
S6
S2
S8
S1
S2
S4

2.960(3)2.992(3)3.098(3)3.120(3)3.149(3)3.218(4)3.375(3)3.440(3)3.494(3)

M1

S4
S1
S3
S8
S7

2.236(4)2.262(4)2.321(3)3.191(4)3.243(4)

M2

S2
S7
S3
S8
S4
S6
S10

2.309(3)2.378(3)2.492(3)2.933(4)3.315(3)3.639(4)3.646(4)

M3

S5
S7
S3
S8
S4
S6
S10

2.435(3)2.458(3)2.749(4)2.799(3)3.343(3)3.634(4)3.764(4)

M4

S8
S6
S7
S10
S9

2.321(4)2.328(4)2.405(4)3.096(4)3.310(4)

M5a

S9
S5
S6
S9
S10
S3

2.759(6)2.770(5)2.808(5)2.819(6)2.829(6)2.848(5)

M5b

S9
S9
S10
S5
S6
S3

2.446(6)2.458(6)2.571(6)2.988(6)3.149(5)3.283(5)

M6a

S4
S6
S10
S5
S9
S10
S8

2.844(3)2.854(3)2.927(4)2.986(3)3.036(4)3.134(3)3.481(4)

M6b

S5
S6
S4
S10
S9
S10

2.51(4)2.61(3)2.72(3)2.82(3)3.28(3)3.55(3)structure, is Ag1.05Pb5.84As4.63Sb4.48S20, with therelative error on the valence equilibrium Ev =+0.15. This formula is not exactly chargebalanced, but it does not take into account thelimited Pb for Tl substitution; the site(s) involvedin this substitution has (have) not been localized,
due to the very similar scattering factors of these
two elements. In addition, it shows a slightly
greater Sb/(Sb+As)at. ratio with respect to theresults of chemical analysis, i.e. 0.49 vs. 0.47.

Crystal-structure description
General organization of carducciite
The general organization of the crystal structureof carducciite is presented in Fig. 3. It belongs to
the N = 4 homologue of the sartorite series and it
shows a homeotypic relationship with dufrénoysite (Moëlo et al., 2008; Table 8). It can be
described as formed by chemically twinned layersof the dufrénoysite type.

FIG. 2. Crystal structure of carducciite: projection of the unit cell along a. Note: for clarity, M5a, M5b, M6a and M6bhave been represented as full circles, despite their partial ﬁlling.

1782

CARDUCCIITE FROM TUSCANYTABLE 7. Bond-valence calculations according to Brese and O’Keeffe (1991).

S1
S2
S3

Pb1

Pb2

0.34
0.12
0.28
0.17
0.30
0.08

0.30
0.11
0.20
0.09

S4
S5
S6
S7
S8

0.16
0.15
0.18

0.33
0.08
0.23
0.21

M1

M2

M3

M4

M5a

M5b

M6a

M6b

1.01

Sanions
1.88

1.11
0.86

0.68

1.08

0.07

1.85
0.08

1.04

0.05

0.10
0.09

0.11
0.07

2.03
0.42

0.04

2.02

0.28
0.40

0.06
0.05

1.98
1.99
2.09
1.95

0.09
0.39

1.02
0.83
1.04

S9

0.45

0.07

0.10
0.09

0.47
0.46

0.25

0.01

1.90

S10

0.98

0.13

0.08

0.34

0.33
0.19

0.03

2.08

2.95
3.00

3.09
3.00

0.54
0.53

1.50
1.41

1.94
1.84

0.19
0.24

0.16

Scations
Theor.*

1.78
2.00

1.71
2.00

0.07
0.08

3.10
3.00

0.92
0.21

2.99
3.00

0.07

In mixed sites, the bond-valence contribution of each cation has been considered according to its occupancy (seeTable 5).
* Theoretical valence on the basis of site occupancies.

The crystal structure of rathite (as well as thatof barikaite) displays walls of ‘standing’ tricapped
trigonal coordination prisms of Pb (prism axis
parallel to a), alternating with slabs (dufrénoysite
layers) composed of ‘lying’ trigonal coordination

prisms of (As,Sb) and Pb, based on SnS archetype(Berlepsch et al., 2002). The structure of
carducciite is basically similar to that describedby Marumo and Nowacki (1965) and Berlepsch etal. (2002) for rathite from Lengenbach and by

FIG. 3. Carducciite structure: general organization. Dashed red lines delimit the N = 4 dufrénoysite-type ribbons,
separated along b by lone-electron-pair micelles (black hatched ellipses). Left: connection along b of Pb tricapped
triangular prisms (grey).

1783

CRISTIAN BIAGIONI ET AL.

TABLE 8. Cell parameters of N = 4 sartorite homologues (P21/c setting for rathite isotypes).
MineralChemical formulaa (Å)b (Å)c (Å)

b (º)

S.G.

Ref.

Dufrénoysite
VeeniteRathiteBarikaite
Carducciite

Pb8As8S20
Pb8(Sb,As)8S20(AgAs)Pb6As8S20
Ag1.5Pb5As5.5Sb4S20(AgSb)Pb6As8S20

7.90
8.44
8.50
8.53
8.49

25.74
26.2
7.97
8.08
8.02

8.37
7.90
25.12
24.95
25.40

90.35
unknown
100.70100.66100.38P21
unknown
P21/c
P21/c
P21/c

(1)
(2)
(3)
(4)
(5)

(1) Marumo and Nowacki (1967); (2) Jambor (1967); (3) Berlepsch et al. (2002); (4) Topa et al. (2013); (5) this work.

Makovicky and Topa (2013) for barikaite. The
walls of ‘standing’ tricapped trigonal prisms,
centred by Pb atoms (and possibly minor Tl) areformed by columns composed of the alternation,
along a, of Pb1 and Pb2 polyhedra sharing faces.
Adjacent columns are connected along b throughedge-sharing, giving rise to the walls. Between
the walls, dufrénoysite layers (N = 4) occur.
The dufrénoysite layer type occurs in different
sulfosalts belonging to the sartorite homologous
series: dufrénoysite, rathite, barikaite, liveingite,baumhauerite, baumhauerite-2a and boscardinite.
In carducciite, within the dufrénoysite layer, there
are two pure (or nearly pure) As (M1) and Sb(M3) sites, two mixed (As,Sb) sites (M2 and M4,
with As > Sb), and two split sites, i.e. an Ag/Sb
split site (M5) and a Pb/As one with Pb > As
(M6). Such an equivalent (Ag,Sb) and (Pb,As)pair is in the same conﬁguration of theconstitutive layer of rathite, barikaite (in bothphases, however, the split site M5 is occupied by
Ag and As) and, in particular, of boscardinite(Orlandi et al., 2012).
Cation coordination and site occupancies
The crystal structure of carducciite contains two
pure Pb sites, four Me3+ sites [where Me is As, Sb,or (As, Sb)], two split sites (an Ag/Sb and a Pb/As
site) and 10 S sites (Table 5). Pb1 and Pb2 are‘standing’ tricapped trigonal coordination prisms,with average bond lengths of 3.188 and 3.205 Å,respectively. The four sites hosting As and/or Sb
can be divided into two mixed (As, Sb) sites, anearly pure As site and a pure Sb site.
The M1 site, with a mean bond length of 2.27 Å
(in good agreement with rathite of Berlepsch etal., 2002 and barikaite, i.e. 2.26 and 2.28 Å,
respectively) and a three-fold coordination, is anearly pure As site; the reﬁnement of its site
1784

occupancy indicates only a very minor Sb
substitution (only 0.02 a.p.f.u. Sb). The coordination is completed by two additional bonds at~3.2 Å.
The M2 and M4 sites are mixed (As, Sb) sites,with reﬁned site occupancy As0.60Sb0.40 andAs0.66Sb0.34, respectively. M2 has a three-foldcoordination, with additional longer bonds at 2.9
and 3.3 Å; a similar coordination is shown by M4,
with three shorter bonds and two longer ones, at
3.1 and 3.3 Å. According to Berlepsch et al.
(2002) and considering only the bonds withMe S distance <2.70 Å, M2 and M4 of rathite
are pure As sites, with average bond lengths of
2.31 and 2.27 Å, respectively, compared with 2.39
and 2.35 Å of carducciite. In the crystal structureof barikaite, the M2 and M4 sites are labelled Me2
and Me3, respectively, and are mixed split (As,Sb) sites; according to Makovicky and Topa(2013), the split sub-positions indicate
As0.55Sb0.45 for the Me2 site and As0.82Sb0.18 forMe3.
M3 is a pure Sb site, as indicated by thereﬁnement of the As vs. Sb site-scattering value. Its
average bond distance is 2.61 Å; M3 has two shortbonds (2.44 and 2.46 Å) and two longer additionalbonds (2.75 and 2.80 Å). This bond distribution issimilar to that found by Berlepsch et al. (2002) for
the split M3b position of rathite, which is occupied
by arsenic; these authors reported two short bonds
at 2.24 and 2.28 Å and two long bonds, at 2.69 and2.73 Å. Whereas in rathite M3 is split into two subpositions (M3a and M3b, occupied by Sb0.265 andAs0.735, respectively), in carducciite there are nohints of such a splitting. In the crystal structure ofbarikaite, the M3 site is labeled as Me4(Makovicky and Topa, 2013), and shows thesame identical features observed in carducciite,that is a pure Sb occupancy and the same bondpattern, with an average bond distance of 2.61 Å.

CARDUCCIITE FROM TUSCANY

sartorite (Berlepsch et al., 2003), boscardinite(Orlandi et al., 2012) and the pair sterryite/
parasterryite (Moëlo et al., 2012).
In carducciite, if only the shortest (= strongest)
Me3+ S bonds are considered (<2.70 Å
see
Moëlo et al., 2012), ‘reduced’ (Sb/As)S3 triangular pyramidal polyhedra appear. The only
exception is represented by the M3 site, which
has only two bonds shorter than 2.70 Å; however,
the third and fourth bonds (M3 S9 and M3 S8)
are only a little longer, being ~2.75 and 2.80 Å,
respectively. The projection perpendicular to a ofone oblique ribbon of the dufrénoysite type(Fig. 4a) reveals the oblique stacking (~45ºrelative to the elongation) of ﬁnite 1D units
elongated along [100]PbS, with the ideal formulaof carducciite, more exactly AgPb6Sb3(As,Sb)4
As2S20 (taking M6 = pure Pb, M1 = pure As andM5a = M5b = 0.50). Without Ag and Pb,(Sb/As)S 3 polyhedra constitute a single
Sb3(As,Sb)4As2S20 polymer (Fig. 4b, No 1).
Nevertheless, in this polymer the M3 position
appears to be a mean position, due to the long
M3 S9 and M3 S8 bonds. Thus, when one of
the two M3 positions is bound to S9, the second
one must be bound to S8. Two choices are
possible (Fig. 4b, No 2 and 3), but choice No 2
seems more probable. Indeed, there is adissymmetry in the two M5b M3 distances, ashort one (3.60 Å) and a long one (3.89 Å). In
choice No 3, the shift of M3 towards S9 will
shorten the M5b M3 distance below 3.60 Å, andthus increase the repulsion between these two Sb
atoms. This is not the case in choice No 2, whichappears more favourable from the energetic pointof view. Considering this choice, the orderedstructure would correspond to the combination of
two polymers, (As,Sb)2AsS7 andSb3(As,Sb)2AsS13.

The two split sites, M5 and M6, are occupied
by Ag/Sb and Pb/As, respectively. The splittingof the M5 site was proposed by Marumo andNowacki (1965), with Ag at the M5a sub-site(site occupancy factor (s.o.f.) 0.57) and As at
M5b (s.o.f. 0.402). This was conﬁrmed byBerlepsch et al. (2002), with Ag(M5a)/As(M5b) = 0.474/0.526; in barikaite, the Ag/As
ratio is 0.53/0.47 (Makovicky and Topa, 2013).
In carducciite, M5a hosts Ag (s.o.f. 0.526), witha distorted octahedral coordination and averagebond length of 2.80 Å, in agreement with 2.77 Å
observed by Berlepsch et al. (2002) for rathiteand by Makovicky and Topa (2013) for barikaite.
On the contrary, whereas the three-fold coordinated M5b positions of rathite and barikaitestudied by these authors show a mean bonddistance of 2.38 and 2.39 Å, respectively, theaverage bond distance of M5b observed in
carducciite is signiﬁcantly longer, i.e. 2.49 Å,ranging from 2.45 to 2.57 Å. The average bonddistance and reﬁned electron density at the M5b
sub-position agree with an occupancy by Sb(s.o.f. 0.474). The M6 site is split into two subpositions, namely M6a and M6b, hosting Pb(s.o.f. 0.92) and minor As (s.o.f. 0.08), respectively. M6a is a ‘lying’ monocapped trigonal
prism, with average bond length of 3.04 Å. As
also pointed out by Berlepsch et al. (2002), thecoordination of M6b is not characteristic ofarsenic, having four bonds ranging between 2.53
and 2.82 Å, and two longer bonds up to 3.53 Å. It
is likely that, owing to the very low occupancy ofthe site, the exact positions of the associated S
ligands cannot be resolved. Makovicky and Topa(2013) observed, for barikaite, the splitting of theM6 site into three sub-positions, namely Ag6,Pb6 and Sb6, with s.o.f. 0.28, 0.43 and 0.29,
respectively.
Polymerization of Me3+S3 triangular pyramidal
polyhedra
Marumo and Nowacki (1965) pointed out that inrathite ‘‘AsS3 pyramids form chains with ﬁnite
lengths’’, i.e. AsmSn polymers. Re-examination of
the structure indicates two possible combinationsof two polymers: (1) As3S7 + As6S13, or (2)As5S11 + As4S9. Reﬁnement of the structure byBerlepsch et al. (2002) shows the validity of
combination 2 (we do not take the mixed (Pb,As)
M6 position into account). Such a polymericorganization was later recognized in various leadsulfosalts: andorite VI (Sawada et al., 1987),

Crystal chemistry of the rathite sub-group of
dufrénoysite homeotypes
Carducciite: a homeotypic derivative ofdufrénoysite
The main characteristic of the crystal structure of
carducciite is its derivation from the dufrénoysite
pole by the complete coupled substitution 2Pb2+ =Ag+ + Sb3+ at the M5 position. This substitution isa case of valency-imposed double site occupancy(Hatert and Burke, 2008). Such a coupled
substitution leads to a space group (P21/c) distinct
from that of dufrénoysite (P21): carducciite is ahomeotype of dufrénoysite.

1785

CRISTIAN BIAGIONI ET AL.

FIG. 4. Polymeric organization of the (Sb,As) atoms with S atoms (short bonds, green) in the dufrénoysite-type
constitutive layer of carducciite. (a) Oblique stacking of 1D units (black shaded lines); (b) ideal Sb3(As,Sb)4As2S20
polymer. No 1: with M3 mean position; No 2: ﬁrst sub-choice for the two effective M3 positions; No 3: second subchoice. Horizontal blue or brown arrows indicate the shifts of M3 towards S8 or S9, and red double arrow the
shortening of the M3 M5b distance. As/M6b with low s.o.f. [0.08 small green circle in (a), with dashed As Sbond], has been omitted in (b).

The rathite sub-group of dufrénoysite
homeotypes
Carducciite is closely related to rathite. It
constitutes a speciﬁc mineral species, and not
simply an Sb-rich variety of rathite, because of
the speciﬁc crystal-chemical role played by Sb3+,
instead of As3+ in rathite, at the M5 position.
Barikaite is also very close to rathite; its P21/n
setting, which is also given for rathite (Topa et al.,2013), can be transformed conveniently into theconventional P21/c setting through the transformation matrix R = (1 0 0, 0 1̄ 0, 1̄ 0 1̄), assuggested by Berlepsch et al. (2002). These
relationships allow one to deﬁne the rathite subgroup of P21/c homeotypes derived from the N =4 dufrénoysite homologue. The unit-cell parameters of rathite, carducciite and barikaite in thisP21/c setting are reported in Table 8.
Crystal-chemical substitutions in the rathite subgroup
The available chemical data of rathite andbarikaite are reported in Table 9. Anotherchemical analysis of rathite was reported by
1786

Nowacki and Bahezre (1963) but did not actually
represent rathite, owing to the absence of Ag,
contrasting with the structure solution of Marumo
and Nowacki (1965) that indicated the occurrenceof this element as an essential component.
Consequently, this chemical data will not be
accounted for.
Figure 5 shows the Pb content vs. (Sb + As)(Fig. 5a) and Ag (Fig. 5b) contents; Pb and (Sb +As) contents have been corrected by subtracting
Tl. The tie-line in this ﬁgure represents thesubstitution Me+ + Me3+ = 2 Me2+ between
dufrénoysite, Pb8As8S20, and the hypothetical
ideal endmember composition Ag2Pb4(As,Sb)10S20. In the framework of the N = 4
homologues of the sartorite series, with generalformula (Ag,Tl)xPb8 2x(As,Sb)8+xS20, rathite andcarducciite correspond to phases having x = 1,
with ideal composition AgPb 6 (As,Sb) 9 S 20 .
Consequently, following Berlepsch et al. (2002),
the chemical formulae of rathite and carducciite
could conveniently be written as (AgAs)Pb6(As,Sb)8S20 and (AgSb)Pb6(As,Sb)8S20, respectively. Barikaite is close to the chemical pole
having x = 1.5, Ag1.5Pb5(As,Sb)9.5S20; its crystal

CARDUCCIITE FROM TUSCANYTABLE 9. Electron microprobe chemical data of rathite and barikaite. Chemical analyses (in wt.%) wererecalculated on the basis of SMe = 16 a.p.f.u. Ev values, Pbcorr. and (Sb + As)corr. are calculated as in
Table 2.
Element
Ag
Tl
Pb
As
Sb
Fe
S
Sum

1

1

1

1

2

2

2

4.18
3.49
39.49
25.68
2.95
0.08
24.50
100.37

4.04
5.10
36.62
26.85
2.42

3.86
4.41
38.51
26.59
2.05

4.13
5.36
36.61
27.31
1.94

3.50
2.10
43.9
26.3
0.15

3.90
1.35
44.8
25.9
0.35

3.85
0.90
45.4
25.3
0.75

24.77
99.80

24.31
99.74

24.48
99.82

23.7
24.4
99.17 100.6

3

4

4

4

4

3.46
5.51
1.07
0.13
45.48 36.18
25.74 15.52
n.d. 18.36

5.87
0.13
35.50
15.77
18.37

4.55
0.07
39.21
15.38
16.68

4.93
0.22
38.19
15.18
17.49

23.7
24.54 23.92
100.00 100.29 99.62

23.98
99.63

23.65
99.55

23.66
99.68

SMe = 16 a.p.f.u.
Ag
1.008 0.971 0.931 0.985 0.855 0.952 0.947 0.855 1.399 1.481 1.176 1.267
Tl
0.444 0.647 0.561 0.675 0.271 0.174 0.117 0.140 0.017 0.017 0.010 0.030
Pb
4.960 4.580 4.836 4.548 5.586 5.694 5.813 5.850 4.782 4.664 5.275 5.108
As
8.920 9.287 9.234 9.382 9.255 9.104 8.959 9.156 5.673 5.730 5.722 5.615
Sb0.630 0.515 0.438 0.410 0.032 0.076 0.163
4.129 4.107 3.818 3.981
Fe
0.037
S
19.883 20.019 19.725 19.649 19.487 20.039 19.610 20.395 20.428 20.358 20.557 20.448
Ev
0.8
0.4
1.8
2.1
3.0
0.1
2.1
1.6
1.2
0.9
1.9
1.5
Pbcorr.
5.848 5.874 5.958 5.898 6.128 6.042 6.047 6.130 4.816 4.698 5.295 5.168(Sb + As)corr.
9.106 9.155 9.111 9.117 9.016 9.006 9.007 9.016 9.785 9.820 9.530 9.566
Sb/(Sb + As)at. 0.066 0.053 0.045 0.042 0.003 0.008 0.018 0.000 0.421 0.418 0.400 0.415(1) Berlepsch et al. (2002); (2) Laroussi et al. (1989); (3) Graeser, unpublished data, in Pring (2001); (4) Topa et al.
(2013).

chemical formula may be written(Ag0.5Sb0.5)(AgAs)Pb5(As,Sb)8S20.
In this multi-component series, starting fromthe pure Pb and As dufrénoysite pole, three kindsof substitution occur: (1) the homovalent substitution As3+ = Sb3+; (2) the heterovalent substitution
2Pb2+ = Ag+ + Me3+ (Me3+ = As3+, Sb3+); and(3) the heterovalent substitution 2Pb2+ = Tl+ +Me3+.
The ﬁrst substitution takes place, in particular,
at the M3 site in rathite and carducciite, or its
equivalent M4 site in barikaite, and, in minor
amounts, at the M2 and M4 (= M3 in barikaite)
sites (Table 10; see also Fig. 6). In particular, theM3 site has a reﬁned site-occupancy(As 0.74 Sb 0.26 ) in rathite from Lengenbach(Berlepsch et al., 2002), whereas it is a pure Sbsite in carducciite and in M4 of barikaite. Indeed,carducciite and barikaite are richer in Sb thanrathite, with an Sb/(Sb+As)at. ratio of 0.47 and0.42 for carducciite and barikaite, respectively, tobe compared with values ranging between 0 and
0.07 for rathite (Table 9).
1787

The second substitution involves addition ofAg, which is required for the chemical stability ofrathite, barikaite and carducciite with respect todufrénoysite. The peculiar crystal-chemical roleof silver in rathite (M5 site) was revealed by the
crystal-structure study of Marumo and Nowacki(1965), reﬁned by Berlepsch et al. (2002). It wasenhanced by the electron microprobe analysis
data of Laroussi et al. (1989). At the M5 site, thetrivalent Me3+ cation could be As in rathite andbarikaite, and Sb in carducciite (Table 10).
Moreover, barikaite shows an Ag excess hosted
at the M6 site, together with Sb.
Finally, rathite from Lengenbach has a variable
but signiﬁcant Tl content, ranging between 0.12
and 0.68 a.p.f.u. Carducciite and barikaite arequite Tl-free, showing only 0.13 and 0.15 wt.% Tl(detection limit, for carducciite analysis,
0.07 wt.%), corresponding to ~0.02 a.p.f.u. inboth species. Thallium shows a clear negative
correlation with lead and carducciite is actuallyricher in lead than rathite (5.91 a.p.f.u., whereas
the values for rathite from Lengenbach range

CRISTIAN BIAGIONI ET AL.

FIG. 5. Pb content (in a.p.f.u.) vs. (Sb + As) content (a) and Ag content (b) in the chemical formulae of members of
the rathite sub-group. Triangles = barikaite. Squares: white = carducciite; grey = rathite. Circles = ideal compositions
for x = 0, 1, 1.5 and 2.

between 4.55 and 5.85 a.p.f.u.). Thallium should
be hosted at the Pb1 and/or Pb2 sites, in agreementwith its typical nine-fold coordination in othersulfosalts, e.g. boscardinite (Orlandi et al., 2012).
If thallium occurs, then the Pb site M6 would be
partly occupied by Me3+ cations, in accordancewith the 2 Pb2+ = Tl+ + Me3+ substitution. This isin agreement with structural data that indicate, forthallium-bearing rathite from Lengenbach, a site
occupancy of Pb0.74As0.26 (although Tl has notbeen localized at Pb1 or Pb2 sites). On this basis,reﬁning Pb vs. As at the M6 split site of1788

carducciite, a site occupancy Pb0.91As0.09 is
proposed, corresponding to 0.18 a.p.f.u., in agreement with a minor importance of the 2Pb2+ = Tl+ +Me3+ substitution. Nevertheless, it is not clear if
Me3+ is preferentially arsenic or antimony. In fact,
the bond distances for the M6b split site in rathiteand carducciite are unusual for arsenic in trigonal
pyramid coordination. According to Berlepsch etal. (2002) it could be due to the low site
occupancy of this position, and the consequentimpossibility of resolving the S disorder associatedwith the Pb As substitution. However, theCARDUCCIITE FROM TUSCANYTABLE 10. Cation site occupancy in rathite, barikaite and carducciite. Corresponding pairs of cations in
dufrénoysite are given for comparison. SP: different cations in split positions. The order of M sites
corresponds to their positions from the border to the centre of their constitutive polymeric units.
Dufrénoysite

RathiteBarikaite

Carducciite(Pb1, Pb4) and(Pb2, Pb3)

Pb1
Pb2

Pb1
Pb2

Pb1
Pb2

As2 and As3

M1

As 1.00

M1

As1 and As4

M2

As 1.00

M2 SP

As8 and As5

M4

As 1.00

M3 SP

Pb7 and As6

M3 SP

As 0.735
Sb 0.265

M4

Pb8 and Pb6

M6 SP

Pb 0.739
As 0.261

M6 SP

As7 and Pb5

M5 SP

As 0.526
Ag 0.474

M5 SP

possibility of a Pb Sb substitution could not be
excluded, as observed in other phases of thesartorite homologous series and particularly inboscardinite (Orlandi et al., 2012) and barikaite(Makovicky and Topa, 2013). Moreover, chemical
data for rathite from Lengenbach indicates theexistence of a Tl-bearing variety of rathite,

As 1.00
As 0.549
Sb 0.451
As 0.821
Sb 0.179
Sb 1.00
Pb 0.434
Ag 0.279
Sb 0.287
Ag 0.529
As 0.471

M1
M2
M4

As 0.98
Sb 0.02
As 0.60
Sb 0.40
As 0.66
Sb 0.34

M3

Sb 1.00

M6 SP

Pb 0.92
As 0.08

M5 SP

Ag 0.526
Sb 0.474

containing ~0.5 Tl p.f.u., and a Tl-poor variety,hosting <0.30 a.p.f.u. of thallium (Table 9). It isnoteworthy that the former shows ~1 a.p.f.u. of Sb,
whereas in the latter Sb is scarce or absent.
Actually, as exempliﬁed by barikaite, the M6 site
is quite ﬂexible, able to host Pb2+, As3+, Sb3+, aswell as Ag+.

FIG. 6. Comparison of polymeric units of rathite, barikaite and carduccite. Only Me3+ cations have been represented.
Dark green circle/area: Sb; light green circle/area: As. Straight line: strong bond; tie-line: medium bond.

1789

CRISTIAN BIAGIONI ET AL.

TABLE 11. Chemical variations in Ag-Pb sulfosalts from the Pollone mine.

Carducciite
Meerschautite
Owyheeite
Parasterryite
Sb-poor sterryite
Sb-rich sterryite

As/(Sb+As)at.

Pb/(Sb+AsBi)at.

Pb/(AgCuTlHg)at.

Ref.

0.531
0.153
0.099
0.391
0.392
0.260

0.649
0.951
0.924
0.859
0.764
0.784

6.03
7.095
4.361
5.329
4.33
4.71

[1]
[2]
[3]*
[4]
[4]
[4]

* Average of two chemical points. [1] this work; [2] Biagioni et al. (in prep.); [3] Carmignani et al. (1976); [4]Moëlo et al. (2011).

Distinction between carducciite, barikaite andrathiteBarikaite, carducciite and rathite are homeotypic
derivatives of dufrénoysite, having a different
space group. This corresponds to the ﬁrst criterionof distinction between homeotypy and isotypy, asdeﬁned by Lima-de-Faria et al. (1990). Althoughthese three species have the same space group,with close unit cells, they are homeotypes
according to the second criterion, i.e. when in
one structure one cation position is replaced by asplit position in the other (distinct topologies).
This is realized when, for instance, a pure As site
is replaced by a split (As, Sb) site (compare M2
sites of rathite and barikaite in Table 10).
Generally, close homeotypes correspond to
distinct mineral species, as exempliﬁed by thenumerous members of the aikinite-bismuthinite
homeotypic series (Moëlo et al., 2008). But it is
not always the case, particularly in the ﬁeld of
sulfosalts, when there are mixed (Sb, As)3+ sites.
In the majority of such compounds, Sb3+ and As3+
have a dissymmetric coordination, with three
short bonds, due to the high stereochemical
activity of their lone electron pair. In mixed (Sb,
As) sites, as As S bonds are shorter than Sb S
bonds (ideally 2.26 and 2.45 Å, respectively), Sb
and As will have necessarily distinct sub-positionsin the S polyhedron, although with the same
topology. If, for instance, in a pure As sulfosalt
minor Sb substitutes for As in at least one As site(without any structural change), this Sb-enrichedderivative will be a homeotypic derivative of thepure As pole, but always corresponding to thesame mineral species. As an example, if there
exists (very probably) an Sb-free rathite, it will bea homeotype of Sb-containing rathite, due to thesplit M3 position (Table 10).
1790

Another homeotypic differentiation is an
artifact due to the quality of structure resolution.
For instance, in carducciite all mixed (As, Sb)sites are unsplit positions, while they are split inbarikaite. On the basis of this sole characteristic,
barikaite and carducciite are homeotypes, but it isdue to the poor quality of the single crystal of
carducciite, which did not allow the Sb and As
sub-positions at the M2 and M4 sites to bedifferentiated.
In some cases, Sb presents only two shortbonds, together with medium ones: Sb3 in
carducciite, Sb2 and Sb4 in barikaite (Fig. 6).
Such sites may correspond to the mean of two
sub-positions, determining two distinct polymericunits (see above for carducciite). In barikaite, Sb2
is associated with a well-deﬁned As2 position;
one of the Sb2 sub-positions is topologically
identical to As2, but not the other.
This general approach is also valuable insulfosalt systematics for other mixed sites withvery distinct cations (size, type of coordination):Pb vs. (Ag + Sb), Bi vs. Sb etc.
As a consequence, we consider that homeotypy
cannot be a criterion for the distinction between
rathite, barikaite and carducciite as mineral
species. Only chemical variations in the ﬁllingof Me sites have to be taken into account, here on
the basis of the criterion of the 50% limit ofsubstitution. According to Table 10: (1) there areno signiﬁcant changes in M1, M2 and M4 (= M3
in barikaite). In particular, Sb s.o.f. in barikaite
and carducciite are always below the 50% limit.
(2) As predominates at M3 of rathite, while M4 ofbarikaite and M3 of carducciite are pure Sb sites;(3) Pb predominates at M6 of rathite andcarducciite, while (Ag + Sb) surpasses the 50%
limit in barikaite, according to the 2 Pb2+ = Ag+ +CARDUCCIITE FROM TUSCANY

Sb3+substitution; (4) in the mixed (Ag+, Me3+) M5
site, As predominates in rathite and barikaite,
against Sb in carducciite.
In the CNMNC-IMA proposal, carducciite has
been deﬁned as a distinct species relative torathite on the sole basis of the ﬁlling of the M5
site, i.e. (Ag + Sb), against (Ag + As) in rathite.
The pure Me3+ sites (M1 to M4) have been
considered as a whole, with a mean Sb ratio
below the 50% limit (47%). Thus, the limit
between carducciite and rathite would correspondto the 50% limit within the M5 position, i.e.
(Ag0.50Sb0.25As0.25).
In their deﬁnition of barikaite, Topa et al.
(2013) point out the ordered distribution of As andSb among pure Me3+ sites, that ‘‘represents afeature which separates it from rathite’’. In
particular, they apply the criterion of the 50%
limit to the pure Sb M4 site alone, corresponding
to the split (As, Sb) M3 site of rathite, todistinguish these two species. Similarly, in themodular description of the barikaite structure,
Makovicky and Topa (2013) take into account the
shortest (As, Sb) S bonds to distinguish ﬁnite
crank-shaft chains (i.e. (As, Sb)mSn polymers as
indicated above), which have different sizes fromthose observed in rathite. It is this difference,
together with As/Sb ordering, which controls thehomeotypic derivation of barikaite from rathite,and thus the distinction between these two species.
As stated above, a small shift of the Sb/As ratio
in such complex structures may induce homeotypic changes, and different polymeric units,
related to Sb/As ordering, in an unchanged
mineral species. For instance, M2 sites ofbarikaite and carducciite have an Sb content justbelow the 50% limit. With a small increase of themean Sb/As ratio, Sb s.o.f. may surpass such alimit: according to Topa et al. (2013), such achange would induce a new mineral species. We
think that such a detailed crystal-chemical
analysis is not strictly pertinent in the ﬁeld ofmineral systematics.
In barikaite, the Sb/(As+Sb)at. mean ratio of pureMe3+ sites is 0.41, clearly below the 50% limit, andlower than in carducciite (47%). According to ourapproach, it would not justify its distinction fromrathite. On the contrary, a speciﬁc feature ofbarikaite is the substitution of (Ag+Sb) to 2Pb at
the M6 site, over the 50% limit (56%). This could
be taken as the criterion for the deﬁnition of
barikaite relative to rathite, as well as carducciite.
On this basis, the structural formulae for the rathite
sub-group would be (S Me = 16 a.p.f.u.):(1) rathite (low Ag, Sb low or absent):(AgAs)M6Pb2Pb4(As,Sb)8S20;(2) barikaite (high Ag, high Sb):
M5
(AgAs)M6(Ag0.5+xSb0.5+xPb1-2x)Pb4(As,Sb)8S20(0 < x < 0.5);(3) carducciite (low Ag, higher Sb):
M5
(AgSb)M6Pb2Pb4(As,Sb)8S20.
M5

Relationship with sterryite and parasterryite
During the study of sterryite and parasterryite,Moëlo et al. (2011) noted that in the pseudoternary system Pb2S2 (Sb,As)2S3 (Ag,Cu)2S,
the sulfosalts closest chemically are the owyheeite
solid-solution ﬁeld and rathite. Owyheeite has
been reported previously from the Pollone mineby Carmignani et al. (1976) on the basis ofelectron microprobe data. Carducciite occurs inthe same assemblage as sterryite; it is noteworthy
that Moëlo et al. (2011) emphasized thatparasterryite can be considered a perfect mixtureof owyheeite and Tl-free rathite. As discussed inthis present paper, carducciite is the Sb-rich, Tlfree homeotype of rathite, and appears more
appropriate as the As-rich component, together
with owyheeite, of the sterryite ‘mixture’.
The occurrence of such sulfosalts (Table 11)
indicates the great potential of the Pollone minefor the study of the paragenetic relationships
between Ag sulfosalts. At Pollone, these phases
are the result of reactions and recrystallizations
during Alpine metamorphism. Up to now,
carducciite has only been observed embedded in
the granoblastic baryte, whereas sterryite andparasterryite also occur in late-stage cavities.
However, a detailed study of the textural relationships between these phases is necessary tounderstand the evolution of the hydrothermal
system at the Pollone mine.
Conclusion

1791

The occurrence of carducciite at the Pollone minebrings useful new data to our knowledge of thesartorite homologous series and of the phaseequilibria in the PbS Ag 2 S As 2 S 3 Sb 2 S 3
system. The richness in Sb of carducciite withrespect to rathite agrees with the usual crystal
chemistry of Pb sulfosalts from Apuan Alps.
Sb-rich analogues or varieties of As sulfosalts
were described, for example, from the Monte
Arsiccio mine, i.e. boscardinite, the Tl-Sb homeotype of baumhauerite, and e.g. protochabournéite(Orlandi et al., 2012, 2013).

CRISTIAN BIAGIONI ET AL.

The crystal chemistry of the dufrénoysite
homeotypic series points to several questions
which must be clariﬁed. The crystal structure ofveenite, the Sb-rich derivative of dufrénoysite(Jambor, 1967) must be resolved, in order toexamine the distribution of Sb among primitive
As positions of dufrénoysite. In the rathite subgroup, there is a competition starting from rathite
between the Sb enrichment, which favours theincorporation of Sb at the M5 position, and the Ag
enrichment, which maintains As at the M5
position, but promotes Sb incorporation at theM6 position. The limit between these two very
close trends, which determines the distinction
between barikaite and carducciite, remains
unknown. Another question is the limit between
rathite and carducciite, i.e. what is the Sb/As ratio
in the solid solution controlling the(Ag0.50Sb0.25As0.25) limit on the M5 position?
Acknowledgements
Electron microprobe analyses were performed
with the help of O. Rouer (CNRS engineer,
Institut des Sciences de la Terre d’Orléans). The
paper was handled by Allan Pring; the commentsof Dan Topa and an anonymous referee helped to
improve the paper.
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