Eur. J. Mineral.
2018, 30, 581–592
Published online 20 December 2017

Minerals and materials:
building principles and applications

Lead-antimony sulfosalts from Tuscany (Italy). XXII. Marcobaldiite,∼Pb12(Sb3As2Bi)S6S21, a new member of the jordanite homologous series
from the Pollone mine, Valdicastello Carducci
CRISTIAN BIAGIONI1,*, MARCO PASERO1, YVES MOËLO2, FEDERICA ZACCARINI3 and WERNER H. PAAR4
1

Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, 56126 Pisa, Italy*e-mail: cristian.biagioni@unipi.it
2
Institut des Matériaux Jean Rouxel (IMN), Université de Nantes, CNRS, 2, rue de la Houssinière, BP 32229,
44322 Nantes Cedex 3, France
3
Resource Mineralogy, University of Leoben, Peter Tunner Str. 5, 8700 Leoben, Austria
4
Department of Chemistry and Physics of Materials, University, Jakob Haringerstr. 2a, 5020 Salzburg, Austria
Abstract: The new mineral species marcobaldiite, ∼Pb12(Sb3As2Bi)S6S21, has been discovered in a single specimen collected in aquartz vein embedded in tourmaline-bearing schist from the Pollone mine, Valdicastello Carducci, Pietrasanta, Apuan Alps, Tuscany,
Italy. It occurs as a black blocky prismatic crystal, up to 1 cm in size, with a metallic luster, associated with Sb-rich tennantite. Under
the ore microscope, marcobaldiite is white, with a distinct anisotropism, with grey to bluish-grey rotation tints. Polysynthetic lamellar
twinning is common and characteristic. Reﬂectance percentages for the four COM wavelengths are [Rmin, Rmax (%), (l)]: 31.6, 40.1
(470 nm), 30.9, 39.6 (546 nm), 30.4, 38.5 (589 nm), and 30.0, 37.6 (650 nm). Electron microprobe analyses gave (average of 10 spot
analyses  in wt%): Pb 64.05(34), Bi 4.24(6), Sb 9.10(14), As 4.51(8), S 17.24(19), total 99.14(53). On the basis of SMe = 18 apfu, theempirical
formula is Pb11.98(4)Sb2.90(3)As2.33(3)Bi0.79(1)S20.80(20). The main diffraction lines, corresponding to multiple hkl indices, are
1.775 (s). The[d in A (relative visual intensity)]: 3.568 (ms), 3.202 (ms), 3.016 (ms), 2.885 (ms), 2.233 (vs), 2.125 (s), 1.848 (s), and
crystal structure study gives a triclinic unit cell,
space group P1 with a = 8.9248(9), b = 29.414(3), c = 8.5301(8) A, a = 98.336(5),b = 118.175(5), g = 90.856(5)°, V = 1944.1(3) A3, Z = 2. The crystal structure has been solved and reﬁned to R1 = 0.067 on the basis of
6188 reﬂections with Fo > 4s(Fo) and 363 reﬁned parameters. Marcobaldiite is a new N = 3.5 homologue of the jordanite homologous
series, characterized by the 1:1 alternation of two kinds of layers of distorted octahedra, three- and four-octahedra thick, i.e. of the kirkiite
and jordanite types, respectively. Layers are connected by one atomic layer of three bicapped trigonal prismatic Pb atoms and one
triangular pyramidal As atom in split position. The name of this new mineral species honours the mineral amateur Marco Baldi (b. 1944)
for his contribution to the knowledge of the mineralogy of the pyrite ± baryte ± iron oxide ore deposits from southern Apuan Alps.
Key-words: marcobaldiite; new mineral; sulfosalt; crystal structure; lead; antimony; arsenic; bismuth; Pollone mine; Apuan Alps.

1. Introduction
The jordanite homologous series, ﬁrst deﬁned by
Makovicky (1989), is a group of lead sulfosalts having
3þ
= As, Sb,
general formula Pb4N 2 Me3þ
6 S4Nþ7 , where Me
Bi (Makovicky et al., 2006). Three mineral species
belonging to this series are reported in Moëlo et al. (2008),
i.e. jordanite, geocronite, and kirkiite. The possibly related
mineral tsugaruite, ideally Pb4As2S7 (Shimizu et al.,1998), has a different crystal structure (Matsushita et al.,2014), even if its details have not been published yet.
Jordanite homologues
are characterized by two short
axes (∼8.5 and ∼9.0 A) and a longer one, whose length
depends on the homologue
order, ranging from ≈26 A
(N = 3: kirkiite) to ≈ 32 A (N = 4: jordanite and geocronite).
The N = 4 isotypic pair jordanite (Pb14As6S23) 
geocronite (Pb14Sb6S23) is well-known from various

localities world-wide, and, considering also synthetic
products (Jambor, 1969), displays a complete solidsolution. On the contrary, kirkiite, ideally Pb10As3Bi3S19,
is exceedingly rare, having been described only in two
localities, the Greek type locality (the Pb-Zn ore deposit ofAghios Philippos, near Kirki, Thrace; Moëlo et al., 1985),
and the high-T fumaroles of La Fossa crater, Vulcano,Aeolian Islands, Italy (Borodaev et al., 1998; Pinto et al.,2006).
In order to fully characterize the occurrence of
geocronite from the Pollone mine, near the small hamletof Valdicastello Carducci, Apuan Alps, Italy, where thismineral has been known since the ﬁrst description given
by Kerndt (1845), Biagioni et al. (2016a) examined both
historical as well as new samples from this locality,
studying them through single-crystal X-ray diffraction andelectron-microprobe analysis. During this investigation, a0935-1221/18/0030-2710 $ 5.40

Downloaded from https://pubs.geoscienceworld.org/eurjmin/article-pdf/30/3/581/4346595/ejm_30_3_0581_0592_biagioni_2710_online.pdf
by University of Arizona user
© 2018 E. Schweizerbart’sche Verlagsbuchhandlung, D-70176 Stuttgart
on 27 September 2018https://doi.org/10.1127/ejm/2018/0030-2710

582

C. Biagioni et al.

Table 1. Sulfosalts identiﬁed in the Pollone ore deposit. In bold, minerals having their type locality at the Pollone mine.
MineralChemical formula

MineralChemical formula

Boulangerite
Bournonite
Carducciite
Chovanite
Diaphorite
Ferdowsiite
Fettelite
Geocronite
Jordanite
Marcobaldiite
Meerschautite
Meneghinite

Pb5Sb4S11
CuPbSbS3(AgSb)Pb6(As,Sb)8S20
Pb28(Sb,As)30S72O
Ag3Pb2Sb3S8
Ag8Sb5As3S16[Ag6As2S7][Ag10HgAs2S8]
Pb14Sb6S23
Pb14As6S23
Pb12(Sb3As2Bi)S6S23(Ag,Cu)5.5Pb42.4(Sb,As)45.1S112O0.8
CuPb13Sb7S24

Owyheeite
Parasterryite
Polloneite
Proustite
Pyrargyrite
Seligmannite
Sterryite
Tennantite
Tetrahedrite
Twinnite
Xanthoconite
Zinkenite

Ag3Pb10Sb11S28
Ag4Pb20(Sb,As)24S58
AgPb46As26Sb23S120
Ag3AsS3Ag3SbS3
CuPbAsS3
Cu(Ag,Cu)3Pb19(Sb,As)22(As–As)S56
Cu6Cu4(Fe,Zn)2As4S13
Cu6Cu4(Fe,Zn)2Sb4S13
PbSbAsS4
Ag3AsS3
Pb9Sb22S42

mineral was found having the two short unit-cellparameters close to those of jordanite homologues andthe longer one intermediate between
those of the N = 3 and
N = 4 members, i.e. ≈29 A. The crystallographic andchemical studies allowed its identiﬁcation as a newhomologue belonging to the jordanite series, i.e. marcobaldiite, with N = 3.5 homologue number. The newmineral and its name have been approved by the
CNMNC-IMA (2015-109). The holotype material isdeposited in the mineralogical collections of the Museodi Storia Naturale, Università di Pisa, Via Roma 79, Calci,
Pisa, Italy, under catalogue number 19709. The name is inhonour of the mineral collector Marco Baldi (b. 1944), for
his contribution to the knowledge of the mineralogy of thepyrite ± baryte ± iron oxide ore deposits from southern
Apuan Alps. Marco Baldi was the ﬁrst to describe theactual occurrence of geocronite crystals from Valdicastello
Carducci (Baldi, 1982). In this way, he contributed to themineralogical rediscovery of the Pollone mine, which
since then has been explored by mineral collectors andmineralogists, leading to the discovery of several rare andnew mineral species, mainly represented by lead sulfosalts(sterryite, parasterryite, carducciite, meerschautite, andpolloneite  Moëlo et al., 2011; Biagioni et al., 2014;
Biagioni et al., 2016b; Topa et al., 2017).
The aim of this paper is the full description of the newmineral species marcobaldiite and the discussion of its
crystal-chemistry in the framework of the jordanite
homologous series.

2. Geological setting
The baryte þ pyrite ± (Pb-Zn-Ag) Pollone ore deposit(latitude 43°570 4700 N, longitude 10°160 1900 E) is locatednear Valdicastello Carducci, Pietrasanta, Tuscany, Italy.
The ore bodies are hosted within a Paleozoic metavolcanic-metasedimentary sequence, metamorphosed up to
greenschist facies conditions during the Alpine orogeny.
Estimates of P–T conditions indicate metamorphic
temperatures up to 350 °C with a pressure of 0.35 GPa.
Higher T values (450 °C) were recorded for mineralizing
ﬂuids (Costagliola et al., 1998). Biagioni et al. (2016a)

described the main geological and structural features of the
Pollone mine and distinguished three kinds of occurrence:(i) lenses of microcrystalline baryte þ pyrite, with the local
presence of interlayers/lenses of galena þ sphalerite,
folded and partially re-worked during the late tectonic
stage evolution of Apuan Alps metamorphic complex (e.
g., Carmignani & Kligﬁeld, 1990); (ii) quartz lensoid
veins, oriented SW-NE, with coarse-grained masses ofgalena, sphalerite, and sulfosalts; and (iii) extension
quartz ± baryte ± sulﬁdes veins, trending N140–170, embedded both in the country rocks and in the ore bodies.
Twenty-four different sulfosalts have been identiﬁed in
the Pollone ore deposit (Table 1). The typical occurrence isrepresented by the microcrystalline baryte þ pyrite orebodies, where sulfosalts are scattered as interstitial grainsor as euhedral prismatic to acicular individuals. Rarely,
they are related to small quartz þ baryte veinlets and smallﬁssures occurring in these ore bodies. This kind of
occurrence is typical for the lead-silver sulfosalts from the
Pollone mine. The quartz ± baryte ± sulﬁdes extension
veins represent another source of sulfosalts. Actually, thewell-crystallized specimens of jordanite and geocronite
were found in the vugs of these veins. Finally, some Ag
sulfosalts have been identiﬁed in the quartz lensoid veinsoriented SW-NE (i.e., diaphorite and pyrargyrite  Frizzo& Simone, 1995).

3. Occurrence and mineral description
Marcobaldiite was identiﬁed in only one sample collected
in quartz extension veins embedded in tourmaline-richschist from the Stanzone tunnel, one of the stopes of the
Pollone mine; in the same vein Sb-rich tennantite was
identiﬁed. Its crystallization is related to the circulation ofhydrothermal ﬂuids during the Tertiary Alpine tectonometamorphic events, favoring the remobilization ofelements from the country rocks and the ore bodies andtheir crystallization in the extension veins (Biagioni et al.,2016a).
Marcobaldiite occurs as a black prismatic crystal
measuring 10 mm  3 mm  3 mm. The presence ofstriations suggests the occurrence of a polysynthetic

Downloaded from https://pubs.geoscienceworld.org/eurjmin/article-pdf/30/3/581/4346595/ejm_30_3_0581_0592_biagioni_2710_online.pdf
by University of Arizona user
on 27 September 2018

Marcobaldiite, a new jordanite homologue

583

Table 3. Electron microprobe analysis of marcobaldiite: chemicalcomposition as wt% (10 spot analyses) and number of atoms per
formula unit (apfu) on the basis of ƩMe = 18 apfu.

Fig. 1. Reﬂected light microscopy image of marcobaldiite, showing
polysynthetic twinning. Holotype material, Natural History
Museum of Pisa University, catalogue number # 19709.

Element

wt%

Range

e.s.d.

Pb
Bi
Sb
As
S
Total

64.05
4.24
9.10
4.51
17.24
99.14

63.52–64.46
4.16–4.35
8.89–9.38
4.35–4.62
16.89–17.42
98.29–100.02

0.34
0.06
0.14
0.08
0.19
0.53

apfu (Me = 18)
Pb
Bi
Sb
As
S
Ev (%)

11.98
0.79
2.90
2.33
20.80
0.8

11.91–12.06
0.77–0.80
2.84–2.96
2.27–2.40
20.47–21.11
0.5–2.6

0.04
0.01
0.03
0.03
0.20
1.1

Ev (%) = [Ʃ(valþ)  Ʃ(val)]  100/Ʃ(val).
Table 2. Reﬂectance data (%) for marcobaldiite in air (COMstandard wavelengths are given in bold).
l/nm

Rmin

Rmax

l/nm

Rmin

Rmax

400
420
440
460
470
480
500
520
540
546

31.2
32.3
32.7
31.8
31.6
31.8
31.4
31.1
31.0
30.9

35.2
39.7
41.7
40.2
40.1
40.1
39.9
39.5
39.5
39.6

560
580
589
600
620
640
650
660
680
700

30.6
30.4
30.4
30.1
30.1
30.2
30.0
29.9
29.6
29.1

39.0
38.5
38.5
38.4
38.1
38.0
37.6
37.6
36.9
36.4

emission line) were: galena (Pb Ma), stibnite (Sb La),
GaAs (As La), pyrite (S Ka), and Bi2Te3 (Bi Ma).
Counting times were 30 s on the peak and 15 s on the rightand left backgrounds. The studied grain proved to be very
homogeneous. Chemical data are given in Table 3.
On the basis of ƩMe = 18 atoms per formula unit (apfu),
theempirical
formulaofmarcobaldiite
isPb11.98Sb2.90As2.33Bi0.79S20.80. The idealized stoichiometric chemical formula of the studied sample isPb12(Sb3As2Bi)S6S21, corresponding to (in wt%) Pb
64.02, Sb 9.40, As 3.86, Bi 5.38, S17.34, sum 100.00.
3.2. Crystallography

twinning, conﬁrmed by reﬂected light microscopy (seebelow). It is brittle, with an irregular fracture. The streak isblack, the luster is metallic. Micro-indentation measurements carried out with a VHN load of 15 g give a meanvalue of 182 kg · mm2 (range: 170–195 kg · mm2),
corresponding to a Mohs hardness of ∼3–3½. Density
was not measured; calculated density is 6.56 g · cm3, on
the basis of the empirical formula.
In plane-polarized incident light, marcobaldiite is whitein color, distinctly bireﬂectant. Between crossed polars, it
is anisotropic, with grey to bluish-grey rotation tints.
Internal reﬂections were not observed. Polysynthetic
twinning is common and characteristic (Fig. 1). The
reﬂectance values of marcobaldiite were determined in air
with WTiC as standard (Table 2).
3.1. Chemical analysis
A grain of marcobaldiite was analyzed with a Superprobe
JEOL JXA 8200 electron microprobe (Eugen F. Stumpﬂlaboratory, Leoben University, Austria). The operating
conditions (WDS mode) were: accelerating voltage 20 kV,
beam current 10 nA, beam size 1 mm. Standards (element,

X-ray powder diffraction pattern of marcobaldiite wascollected using a 114.6 mm Gandolﬁ camera with Niﬁltered Cu Ka radiation. The observed pattern, comparedwith the calculated one (obtained using the software
PowderCell; Kraus & Nolze, 1996), is reported in Table 4.
Owing to the multiplicity of indices for the majority of theobserved diffraction lines, the unit-cell parameters were
not reﬁned from X-ray powder diffraction data.
Single-crystal X-ray intensity data collection was
performed using a Bruker Smart Breeze diffractometer(50 kV, 30 mA) equipped with a CCD 4k low noise area
detector. Graphite monochromatized Mo Ka radiation wasused. The detector-to-crystal working distance was
50 mm. A total of 6008 frames was collected in v scanmodes, in 0.25° slices. Exposure time was 25 s per frame.
The data were integrated and corrected for Lorentzpolarization, background effects, and absorption, using the
package of software Apex2 (Bruker, A.X.S. Inc., 2004),
resulting in a set of 6790 independent reﬂections. The
reﬁned unit-cell parameters
are a = 8.9248(9), b = 29.414

b = 118.175(5),(3), c = 8.5301(8) A, a = 98.336(5),g = 90.856(5)°, V = 1944.1(3) A3. The statistical tests on|E| values (|E2– 1| = 0.993) suggested the possible

Downloaded from https://pubs.geoscienceworld.org/eurjmin/article-pdf/30/3/581/4346595/ejm_30_3_0581_0592_biagioni_2710_online.pdf
by University of Arizona user
on 27 September 2018

584

C. Biagioni et al.

Table 4. X-ray powder diffraction data for marcobaldiite.
Iobs

dobs

Icalc

dcalc

hkl

Iobs

dobs

Icalc

dcalc

hkl

w
w

4.45
3.835

w

3.737

8
25
6
5
45
18
20
7
21
25
40
17
17
26
11
14
28
19
52
100
27
30
29
9
30
28
12
35
13
36
10
5
20
28
4
22
5
19
6

4.406
3.832
3.756
3.735
3.692
3.683
3.676
3.596
3.591
3.577
3.555
3.448
3.431
3.398
3.398
3.384
3.314
3.274
3.259
3.219
3.219
3.208
3.109
3.088
3.075
3.032
3.023
2.991
2.908
2.902
2.846
2.841
2.839
2.795
2.755
2.721
2.720
2.662
2.612

211
210
230
212
220
222
032
012
240
232
042
022
242
250
052
232
240
032
252
090
062
212
250
042
262
072
252
270
260
052
082
322
262
280
152
062
122
272
290

vw
w
vw

2.553
2.489
2.442

8
5
3
2
2
1
1
5
48
6
6
5
46
7
54
9
12
13
3
5
6
20
6
8
6
20
6
6
9
17
7
16
7
6
5
5
12
12
12

2.568
2.496
2.434
2.391
2.385
2.342
2.297
2.241
2.240
2.240
2.229
2.204
2.203
2.118
2.110
2.107
2.094
2.074
2.028
2.022
1.986
1.957
1.956
1.916
1.906
1.895
1.880
1.868
1.847
1.843
1.839
1.835
1.811
1.798
1.778
1.749
1.705
1.658
1.609

1 10 2282
2 10 1082
2 10 219 2
162
1 10 222 2
2 11 2
2 10 00 12 2422
370
204
2 12 2
2 11 00 13 2380
2 13 02 13 2472
0 14 2420
2 14 0294
0 12 2424
2 13 2
2 11 2
470
272
07 4
024
08 4
2 14 2
4 11 2292
0 18 0

ms

m

3.568

3.404

m

3.256

ms

3.202

m

3.075

ms

3.016

ms

2.885

m

2.832

w
vw

2.789
2.756

mw

2.707

vw
w

2.652
2.606

mw

2.388

vw
w

2.347
2.294

vs

2.233

s

2.125

vw
w
w
mw

2.072
2.035
2.020
1.980

mw

1.950

mw

1.911

m

1.878

s

1.848

vw
s
w
w
w
w

1.797
1.775
1.753
1.716
1.661
1.608



Note: Intensities and dhkl (in A) were calculated using the software PowderCell 2.3 (Kraus & Nolze, 1996) on the basis of the structural model
given in Table 5. The eight strongest reﬂections are given in bold. Only reﬂections with Icalc ≥ 5 were reported, if not observed. Observed
intensities were visually estimated (vs = very strong; s = strong; ms = medium-strong; m = medium; mw = medium-weak; w = weak;
vw = very weak).

centrosymmetricity of marcobaldiite. Consequently, thecrystal structure was solved in the space group P1 using
Shelxs-97 (Sheldrick, 2008). Scattering curves for neutral
atoms were taken from the International Tables for
Crystallography (Wilson, 1992).
In the ﬁrst step, the positions of the heavier atoms (Pb,
Bi, Sb) were found; through successive difference-Fouriermaps, the other atom positions were located. In the crystal
structure of marcobaldiite, there are eighteen independent
cation positions (one of them split) and twenty-one S sites.
Among cation sites, twelve Pb positions and six (Sb/As)
sites were identiﬁed on the basis of site scattering and Me–
S distances. The site occupancy factors (s.o.f.) of the Pb
positions were initially reﬁned using the scattering curveof Pb vs □ and they were found to be fully occupied. The

six (Sb/As) positions were reﬁned using the scattering
curves of Sb vs As. Whereas four of them are mixed (Sb/As)
positions, with variable As and Sb contents, Sb4 was foundto be completely occupied by Sb only, whereas an atom
heavier than Sb partially occupies the site ﬁnally labeledPb9. Consequently, the s.o.f. of this site was modeled using
the curve of Pb and Sb, giving a s.o.f. Pb0.61Sb0.39. Afterseveral cycles of isotropic reﬁnement using Shelxl-2014(Sheldrick, 2015), the R1 converged to 0.087. By reﬁning theanisotropic displacement parameters for cations only, thereﬁnement yielded a R1 value of 0.071.
Chemical analysis showed the presence of 0.79 Bi apfu.
Owing to the similar scattering factors of Pb (Z = 82) andBi (Z = 83), it is not possible to distinguish these two atoms
on the basis of the site scattering. In order to solve thisDownloaded from https://pubs.geoscienceworld.org/eurjmin/article-pdf/30/3/581/4346595/ejm_30_3_0581_0592_biagioni_2710_online.pdf
by University of Arizona user
on 27 September 2018

Marcobaldiite, a new jordanite homologue

Table 5. Crystal data and summary of parameters describing datacollection and reﬁnement for marcobaldiite.
Crystal data
Crystal size (mm)Cell setting, space groupa (A )
b (A
)

c (A)
a (°)
b (°)
g (°)V (A3)
Z

0.09  0.08  0.04
Triclinic, P1
8.9248(9)29.414(3)8.5301(8)98.336(5)118.175(5)90.856(5)1944.1(3)2Data collection and reﬁnement

Radiation, wavelength (A)Temperature (K)2umax (°)
Measured reﬂections
Unique reﬂections
Reﬂections with Fo>4s(Fo)Rint
Rs

Mo Ka, l = 0.71073
293
50.29
41210
6790
6188
0.04090.026910  h  10,
Range of h, k, l
34  k  34,
10  l  10
R [Fo >4s(Fo)]0.0668R (all data)
0.0702wR (onF 2o )0.2228Goof
1.093
Number of least-squares parameters 363
10.88 (at 0.97 A from Pb14)
Maximum andminimum residual3.76 (at 1.05 A from S8)
peak (e A3)

585

Atomic coordinates, site occupancy factors, andequivalent isotropic displacement parameters of marcobaldiite are given in Table 6. The unit cell is represented inFig. 2.

4. Crystal structure description
4.1. General organization
Marcobaldiite is the N = 3.5 member of the jordanite
homologous series. Following the modular description
given by Makovicky et al. (2006) for the N = 3 homologue
kirkiite, the crystal structure of marcobaldiite (Fig. 3) canbe described as formed by a stacking sequence of distorted
layers of octahedra and trigonal prismatic layers parallel to{0 1 0} and sharing S atoms along their boundaries. N = 3
kirkiite-type layers and N = 4 jordanite-type layers, threeand four-octahedra thick respectively, alternate along[0 1 0] in a 1:1 ratio, separated by one atomic slab of threebicapped trigonal prismatic (Pb, Bi) atoms and one
triangular pyramidal As atom (split position).
Alternatively, the crystal structure can be described as
formed by (1 1 1) slabs of distorted PbS archetype (e.g.,Moëlo et al., 1985; Makovicky, 1989), or (210) slabs of
SnS archetype. The broadness of the two kinds ofoctahedral layer corresponds to three and four subcells of
SnS or PbS. Within each layer, lone-electron-pairs oftrivalent Sb and As, at the opposite side of shortest (i.e.
strongest) (Sb/As)–S bonds, are directed towards acommon oblique interspace, to form so-called loneelectron-pair micelles (Fig. 3).
4.2. Cation coordinations and site occupancies

indetermination, their bond valence sums (BVS), calculated using the bond parameters of Brese & O’Keeffe(1991), were taken into account. An examination of the
BVS at the different Pb and (Pb/Sb) sites suggests that Bi
is not preferentially partitioned at any speciﬁc position, but
it would be statistically distributed among some Pb
positions. Bismuth was located in the four Pb sites having
the highest BVS values, i.e. Pb1, Pb8, Pb15, and Pb16,
with a Bi content not exceeding 0.15 apfu in each position.
The BVS at the Pb9 position, containing 0.39 Sb, agrees
with a mixed (Pb,Sb) occupancy, and not with a mixed (Bi,Sb) or (Pb,Sb,Bi) occupancy.
The ﬁnal anisotropic model for all the atom positions gave
R1 = 0.067 for 6188 reﬂections with Fo > 4s(Fo) and 363
reﬁned parameters. Further details of data collection andreﬁnement are given in Table 5. The occurrence of relatively
high maximum and minimum
residuals in the difference
Fourier map (ca. 11 e A3), as well as some short As–S
distances at the As17 split position, is a common feature forjordanite homologues (e.g., Biagioni et al., 2016a). It could
be likely related to the widespread twinning shown by theseminerals and to the possible presence of stacking faults in thealternation of N = 3 and N = 4 slabs, giving rise to kirkiitelike and jordanite/geocronite domains within marcobaldiite,
contributing in this way to the observed disorder.

Among cation positions, there are twelve Pb or mixed (Pb,
Bi) sites, one pure Sb position, a mixed (Pb, Sb) site, one
pure split As position, and three mixed (Sb/As) sites withdifferent As/(AsþSb) atomic ratios. Cation characteristics(selected bond distances, mean bond distances, and bondvalence sums) are summarized in Table 7, while bondvalence sums on S atoms are given in Table 8.
Lead atoms are six- to eight-fold coordinated,with
average bond distances ranging from 2.996 A for the sixfold coordinated Pb10 site to 3.076 A for the eight-foldcoordinated Pb16 position. Pb3, Pb6, Pb10, and Pb11 havea distorted octahedral coordination; actually, the coordination number of Pb6 is increased to seven when S21b site
is occupied. These Pb sites have a pure Pb occupancy, inagreement with their BVS ranging from 1.95 to 1.98
valence unit (v.u.). Pb18 have a six-fold coordination
corresponding to a trigonal prismatic polyhedron; two
additional very long Pb–S bonds, ranging between 3.83
and 3.91 A, give rise to a bicapped trigonal prism. The Pb
atom hosted at this position is underbonded, with a BVS of
1.77 v.u. A seven-fold coordination is shown by Pb1, Pb2,
Pb7, Pb8, and Pb14 (when S21a is occupied). The
occupancies of these sites are represented by Pb only (Pb2,
Pb7, and Pb14 sites) or by Pb and Bi atoms (Pb1 and Pb8),
with a 85:15 Pb-to-Bi atomic ratio. These agree with the

Downloaded from https://pubs.geoscienceworld.org/eurjmin/article-pdf/30/3/581/4346595/ejm_30_3_0581_0592_biagioni_2710_online.pdf
by University of Arizona user
on 27 September 2018

586

C. Biagioni et al.



Table 6. Atomic coordinates, site occupancy factors (s.o.f.), and equivalent isotropic displacement parameters (A2) for marcobaldiite.
Sites.o.f.

x

y

z

Ueq

Pb1
Pb2
Pb3
Sb4
As5
Pb6
Pb7
Pb8
Pb9
Pb10
Pb11
Sb12
As13
Pb14
Pb15
Pb16
As17a
As17b
Pb18
S1
S2
S3
S4
S5
S6
S7
S8
S9
S10
S11
S12
S13
S14
S15
S16
S17
S18
S19
S20
S21a
S21b

Pb0.85Bi0.15
Pb1.00Pb1.00
Sb1.00As0.63(3)Sb0.37(3)Pb1.00Pb1.00Pb0.85Bi0.15
Pb0.61(1)Sb0.39(1)Pb1.00Pb1.00Sb0.98(3)As0.02(3)As0.91(3)Sb0.09(3)Pb1.00Pb0.85Bi0.15
Pb0.85Bi0.15
As0.75(1)As0.25(1)Pb1.00
S1.00
S1.00
S1.00
S1.00
S1.00
S1.00
S1.00
S1.00
S1.00
S1.00
S1.00
S1.00
S1.00
S1.00
S1.00
S1.00
S1.00
S1.00
S1.00
S1.00
S0.75(1)S0.25(1)0.8503(1)0.8518(1)0.2253(1)0.2412(2)0.3689(3)0.3821(2)0.7725(1)0.7695(1)0.0830(2)0.0780(1)0.6128(1)0.5985(2)0.2850(3)0.2937(2)0.4812(2)0.4818(2)0.9939(4)0.9756(12)0.0467(2)0.6054(8)0.6316(8)0.0088(8)0.9991(8)0.6084(8)0.6113(8)0.2267(8)0.2236(9)0.5456(8)0.5942(8)0.8941(9)0.8730(8)0.1968(8)0.1985(8)0.4821(8)0.4785(8)0.1671(9)0.1711(8)0.8506(8)0.8518(8)0.2244(10)0.233(3)0.38701(4)0.38638(4)0.49413(4)0.50143(6)0.39399(8)0.39554(4)0.16711(4)0.16641(4)0.05688(5)0.05992(4)0.04819(4)0.05375(6)0.15729(9)0.16075(4)0.27712(4)0.27741(4)0.30213(11)0.2494(3)0.27511(4)0.3514(2)0.3389(2)0.4443(2)0.4492(2)0.4537(2)0.4537(2)0.3527(2)0.3538(2)0.1986(2)0.2136(2)0.1089(2)0.1013(2)0.0032(2)0.0050(2)0.0967(2)0.0960(2)0.1958(2)0.1962(2)0.2722(2)0.2734(2)0.2630(3)0.2882(10)0.4904(2)0.9939(2)0.7368(2)0.2478(2)0.0047(3)0.5075(2)0.8456(1)0.3381(2)0.9425(2)0.4471(2)0.9512(2)0.4500(2)0.8444(4)0.3477(2)0.2586(2)0.7431(2)0.2707(4)0.2340(14)0.7796(2)0.0996(8)0.6100(8)0.3618(8)0.8435(8)0.4324(8)0.8754(8)0.1134(9)0.7092(9)0.9932(8)0.5278(8)0.1302(9)0.6092(8)0.2106(9)0.7444(8)0.6306(8)0.1916(8)0.6078(9)0.0017(9)0.3915(9)0.9742(9)0.3651(10)0.381(3)0.0199(3)0.0199(3)0.0213(3)0.0116(4)0.0171(8)0.0258(3)0.0192(3)0.0194(3)0.0230(3)0.0195(3)0.0201(3)0.0146(6)0.0157(9)0.0243(3)0.0238(3)0.0249(3)0.0146(7)0.0146(7)0.0347(4)0.0161(12)0.0162(12)0.0175(13)0.0150(12)0.0159(12)0.0145(12)0.0216(13)0.0227(14)0.0150(12)0.0166(12)0.0189(13)0.0148(12)0.0169(12)0.0167(12)0.0153(12)0.0159(12)0.0236(14)0.0205(13)0.0222(14)0.0196(13)0.0111(15)0.0111(15)BVS calculation, resulting in values ranging from 1.94 to
2.02 v.u. for the pure Pb sites and BVS of 2.11 and 2.07 v.u.
for the mixed (Pb, Bi) positions. Finally, the Pb15 andPb16 sites have a bicapped trigonal prismatic coordination
and a mixed (Pb0.85Bi0.15) site occupancy. Their BVS
values are 2.09 and 2.11 v.u., respectively.
Five Me3þ positions occur in the crystal structure of
marcobaldiite, i.e. Sb4, As5, Sb12, As13, and the split site
As17. Taking into account the shortest〈Me–Sidistances (=
the strongest bonds: Me–S < 2.70 A), these sites display a
trigonal pyramidal coordination, with Me occupying theapex of the pyramid. The coordination sphere is completed
by three additional longer bonds. Sb4 is a pure
Sb position,
with an average 〈Me–Si distance of 2.504 A and a BVS of
2.94 v.u. Antimony is dominant also at the Sb12 position,
having a reﬁned s.o.f.
of Sb0.98As0.02. The average 〈Me–Si

distance is 2.462 A and the BVS indicates moderate

overbonding (3.15 v.u.). As5, As13, and As17 are three
As-dominant positions showing increasing As contents.
Indeed, the reﬁned s.o.f. point to As0.63Sb0.37,
As0.91Sb0.09, and As1.00, respectively. Actually, the As17
site is split into two sub-positions (As17a and As17b)
having a partial occupancy (0.75 and 0.25, respectively) inorder to avoid too-short Me–Me and Me–S distances. S21
is also split in two sub-positions S21a and S21b, with s.o.f.
0.75 and 0.25, respectively. As a consequence, As17a,
shifted towards the N = 3 layer, is bound to S21a, andAs17b to S21b.
Taking into account the reﬁned s.o.f. at As5 and As13,
the calculated BVS at these positions are relatively high(3.31 and 3.29 v.u., respectively). The higher As contents
result indecreasing mean 〈Me–Si distances (2.325 and
2.262 A for As5 and As13, respectively). The mean bonddistances observed at the As17 sub-sites are shorter thanDownloaded from https://pubs.geoscienceworld.org/eurjmin/article-pdf/30/3/581/4346595/ejm_30_3_0581_0592_biagioni_2710_online.pdf
by University of Arizona user
on 27 September 2018

Marcobaldiite, a new jordanite homologue587

Fig. 2. Projection along c of the crystal structure of marcobaldiite.

Fig. 3. Modular organization of the crystal structure of marcobaldiite. Alternating oblique N = 3 and N = 4 layers are separated by single slabs
TP of trigonal prismatic Pb and split As17a/As17b. The three shortest (Sb/As)–S and (Pb,Sb)–S bonds have been enhanced. Shaded ellipses:lone-electron-pair micelles of trivalent Sb and As. Within every N layer, numbers indicate the octahedra sequences.

the ideal one, owing to the average nature of the ligand
positions, related to the statistical occupancy of such subsites. This explains the too high BVS obtained (3.35 and3.74 v.u., assuming the full-occupancy of the sites).
The crystal structure of marcobaldiite is completed by thePb9 position, within the N = 4 layer, having a distorted
octahedral
coordination and an average bond distance of
2.922 A. The reﬁned s.o.f. points to a mixed site occupancy
Pb0.61Sb0.39.Assumingsuchasiteoccupancy,thecorresponding weighted BVS, 2.35 v.u., ﬁts the theoretical one, i.e.
2.39 v.u.

5. Crystal-chemistry of jordanite homologues
5.1. Structural formula
As described above, the crystal structure of marcobaldiite
can be considered as a 1:1 alternation of N = 3 (kirkiitetype) and N = 4 (jordanite-type) octahedral layers, separated by a layer formed by Pb trigonal prismatic polyhedra
and one As trigonal pyramid (Fig. 3). The N = 3 layer ofmarcobaldiitehaschemicalcomposition[Pb3(Pb0.85Bi0.15)(Sb1.37As0.63)Ʃ2S8]1.85. This chemistry
can be compared with that given by Makovicky et al.

(2006) for the N = 3 octahedral layer in kirkiite, i.e.
[Pb3(Pb0.75Bi0.25)(As1.42Bi0.58)Ʃ2S8]1.75. Figure 4 (top)shows the comparison between the N = 3 layers inmarcobaldiite and kirkiite, whereas the site occupancies
are compared in Table 9. The N = 4 layer (Fig. 4, bottom)
has chemical composition [Pb4(Pb0.85Bi0.15)(Pb0.61Sb0.39)(Sb1.07As0.93)Ʃ2S10]1.46 and can be compared with that ofjordanite isotypes from the Pollone mine (Biagioni et al.,2016a), having a chemistry [Pb5(Pb0.50Sb0.50)(Sb0.611.5. Finally, the layer composed by
1.23As1.39-0.77)Ʃ2S10]
Pb trigonal prisms and split As site has chemicalcomposition [Pb(Pb0.85Bi0.15)2AsS3]þ3.3, to be comparedwith [Pb3AsS3]þ3 in jordanite isotypes and[Pb2(Pb0.50Bi0.50)AsS3]þ3.5 in kirkiite.
The crystal-chemical formula of marcobaldiite can beobtained by the sum of the chemical compositions of the
N = 3, N = 4 and the trigonal prismatic atomic layers:[Pb3(Pb0.85Bi0.15)(Sb1.37As0.63)Ʃ2S8]1.85 þ [Pb4(Pb0.85Bi0.15)(Pb0.61Sb0.39)(Sb1.07As0.93)Ʃ2S10]1.46 þ [Pb(Pb0.85Bi0.15)2
AsS3]þ3.30 = Pb8(Pb0.85Bi0.15)4(Pb0.61Sb0.39)(As2.56 Sb2.44)Ʃ5
S21, that is Pb12.01(Sb2.83As2.44Bi0.60)Ʃ5.99S21, to be compared with the formula obtained through chemical analysis,i.e. Pb11.98(Sb2.90As2.33Bi0.79)Ʃ6.02S20.80. It is close to theideal stoichiometric formula Pb12(Sb3As2Bi)S21.

Downloaded from https://pubs.geoscienceworld.org/eurjmin/article-pdf/30/3/581/4346595/ejm_30_3_0581_0592_biagioni_2710_online.pdf
by University of Arizona user
on 27 September 2018

588

C. Biagioni et al.



Table 7. Selected bond distances (in A) and bond-valence sums (BVS  in valence unit, v.u.) for cation sites in marcobaldiite.
–S3
–S5
–S4
–S1
–S2
–S8
–S19

2.823(6)2.856(6)2.956(6)3.004(6)3.012(6)3.208(7)3.361(7)Average
BVS

3.031
2.11

–S4
–S6
–S5
–S4
–S3
–S5

2.482(6)2.496(6)2.535(6)3.202(6)3.217(6)3.330(6)Average
BVS

2.504
2.94

–S15
–S9
–S11
–S10
–S12
–S20
–S18
Average
BVS

2.936(6)2.944(6)2.962(6)2.969(6)3.041(6)3.112(7)3.204(7)
3.024
2.00

Pb8

Pb10

–S14
–S12
–S14
–S13
–S11
–S15
Average
BVS

2.747(6)2.951(6)2.978(6)3.013(6)3.015(6)3.270(6)
2.996
1.95

As13

–S18
–S17
–S9
–S15
–S16
–S12

2.241(7)2.270(7)2.276(6)3.433(6)3.437(6)3.486(7)Average
BVS

2.262
3.29

–S2
–S21b
–S21a
–S10
–S20
–S1
–S8
–S9
–S17
Average
BVS

2.881(6)2.90(3)2.904(8)2.950(6)2.955(6)3.170(6)3.186(7)3.252(6)3.306(7)3.0761/3.0752
2.11

Pb1

Sb4

Pb7

Pb16

–S6
–S1
–S3
–S4
–S2
–S7
–S20

2.866(6)2.963(6)2.989(6)2.999(6)3.009(6)3.224(7)3.303(7)Average
BVS

3.050
1.94

–S7
–S1
–S8
–S5
–S6
–S4

2.310(7)2.332(6)2.332(7)3.411(6)3.419(6)3.456(6)Average
BVS

2.325
3.31

–S11
–S16
–S10
–S9
–S12
–S19
–S17
Average
BVS

Pb11

Pb14

Pb2

As5

As17a

–S3
–S4
–S3
–S5
–S6
–S6

2.692(7)2.942(6)2.973(6)3.040(6)3.054(6)3.371(6)Average
BVS

3.012
1.98

Pb6

–S2
–S5
–S7
–S6
–S8
–S21b
–S3
Average
BVS

2.682(6)2.975(6)3.022(7)3.039(6)3.054(7)3.23(3)3.384(7)3.0261/3.0552
1.96

2.879(7)2.936(6)2.965(6)2.976(6)3.031(6)3.102(7)3.202(7)
3.013
2.07

Pb9

–S13
–S14
–S13
–S12
–S11
–S16

2.679(6)2.682(6)2.768(7)3.069(6)3.109(7)3.223(6)Average
BVS

2.922
2.35

–S11
–S13
–S15
–S14
–S16
–S14
Average
BVS

2.698(7)2.960(6)3.007(6)3.024(6)3.025(6)3.384(7)
3.016
1.95

Sb12

–S12
–S15
–S16
–S13
–S14
–S13
Average
BVS

2.450(6)2.456(6)2.481(6)3.320(7)3.334(7)3.360(7)
2.462
3.15

–S10
–S18
–S17
–S21a
–S16
–S15
–S11

2.694(6)2.979(7)3.000(7)3.077(8)3.091(6)3.128(6)3.355(7)Pb15

Average
BVS

3.0461/3.0412
2.02

–S21b
–S21a
–S2
–S19
–S10
–S7
–S1
–S9
–S18
Average
BVS

2.86(2)2.881(7)2.939(6)2.951(6)2.983(6)3.150(7)3.170(6)3.248(6)3.269(7)3.0741/3.0712
2.09

–S19
–S21a
–S20
–S7
–S8
–S1

2.224(7)2.231(8)2.245(7)3.384(7)3.394(8)3.498(7)

As17b

–S19
–S20
–S21b
–S18
–S17
–S9

2.162(12)2.190(12)2.22(3)3.445(12)3.460(12)3.560(12)Average
BVS

2.233
2.52

Average
BVS

2.191
0.93

Pb3

Pb18

–S19
–S20
–S17
–S8
–S18
–S7
–S10
–S2
Average
BVS

2.910(7)2.921(7)3.053(7)3.065(7)3.094(7)3.096(7)3.829(6)3.908(6)
3.023
1.77

Notes: (i) average bond distances for (Sb/As) sites were calculated taking into account Me–S distances shorter than 2.70 A. (ii) Superscripts“1” and “2” indicate coordinations involving S21a and S21b, respectively. The corresponding BVS involving the split S21 site have been
weighted in agreement with the s.o.f. of the sub-positions S21a (0.75) and S21b (0.25). (iii) For sites with mixed occupancy, the BVS havebeen weighted according to the reﬁned s.o.f. (iv) The average distance at Pb18 site has been calculated taking into account only the six
shortest Pb–S distances.
Downloaded from https://pubs.geoscienceworld.org/eurjmin/article-pdf/30/3/581/4346595/ejm_30_3_0581_0592_biagioni_2710_online.pdf
by University of Arizona user
on 27 September 2018

Marcobaldiite, a new jordanite homologue589

Fig. 4. Comparison between N = 3 and N = 4 octahedral layers of marcobaldiite with those occurring in kirkiite (top) and jordanite/geocronite(bottom).

Table 8. Bond valence sums (BVS  in valence unit, v.u.) for S
atoms in marcobaldiite.
Site

BVS

Site

BVS

S1
S2
S3
S4
S5
S6
S7
S8
S9
S10
S11

2.05
2.06
2.01
2.07
1.96
1.99
1.99
1.92
1.99
2.01
2.01

S12
S13
S14
S15
S16
S17
S18
S19
S20
S21a
S21b

2.13
1.94
2.01
2.02
1.96
1.90
1.98
2.21
2.13
2.12
2.09

Note: The BVS at S21a and S21b sites have been calculated
assuming their full-occupancy.

All known metalloid ratios of jordanite homologues
have been represented in the As-Sb-Bi sub-system (Fig. 5).
Taking into account the ideal formulae of geocronite,
Pb14Sb6S23, and As-rich kirkiite, Pb10As4Bi2S19, one cansee that the ideal formula of marcobaldiite is quite
identical to the 1:1 mixture of these homologues, having
formula Pb24(Sb6As4Bi2)S42 = 2  Pb12(Sb3As2Bi)S21.
Since Bi is not dominant at any site of the crystal
structure of marcobaldiite, the structural formula derived
through the single-crystal study could be reduced to astoichiometric one taking into account the coupled
substitution Pb2þ þ Sb3þ = Bi3þ þ Pb2þ. Indeed, ca.
0.60 Bi apfu are distributed among four Pb positions(i.e., Pb1, Pb8, Pb15, and Pb16), whereas Sb is replaced by
ca. 0.60 Pb apfu at the Pb9 position. Subtracting Bi, thestructural formula become Pb12(Sb3.44As2.56)Ʃ6S21.

5.2. Bismuth in the jordanite homologous series
The occurrence of relatively high contents of Bi in thisnew mineral species is a rare feature shown by jordanite
homologues. Indeed, the ﬁndings of high Bi contents inthese minerals are limited to three localities, i.e. Aghios
Philippos, Kirki, Thrace, Greece (Moëlo et al., 1985,
1990); La Fossa crater, Vulcano, Aeolian Islands, Italy(Borodaev et al., 1998; Pinto et al., 2006); and the Pollone
mine, Apuan Alps, Tuscany, Italy.
Kirkiite shows Bi contents up to 15.5 and 18.27 wt% insamples from Kirki and Vulcano, respectively (Moëlo et al.,
1985; Pinto et al., 2006), corresponding to a maximum
content of 3.09 Bi apfu, close to the ideal formula
Pb10As3Bi3S19 (Fig. 5). Moreover, Moëlo et al. (1990)
reported the identiﬁcation of an Sb-bearing variety of
kirkiite, with two samples having average chemicalcompositions of Pb10.21(As3.48Sb1.36Bi1.16)S19.70 andPb10.27(As3.89Sb1.05Bi1.05)S19.90 (Fig. 5), ideally close toPb10(As4SbBi)S19. This is the lowest Bi content reported for
the N = 3 homologue of the jordanite series. The solution of
the crystal structure of kirkiite by Makovicky et al. (2006)
could suggest the cross-substitution of Pb and Bi at the Pb4
and Pb6 positions, with Bi being preferentially partitioned at
the Bi1/As1 split site. The chemical variability reported byMoëlo et al. (1985, 1990) could be interpreted in the light ofthis crystal-chemical behaviour, with the composition of the
Sb-rich variety corresponding to the occurrence of a mixed(Bi0.50Sb0.50) occupancy at the Bi1/As1 site of Makovicky
et al. (2006). In conclusion, available chemical data suggeststhat Bi is always present in the N = 3 homologue kirkiite.
On the contrary, the N = 4 homologues are usually Bipoor, with Bi contents less up ca. 0.50 wt% (e.g., Pollone
mine, Apuan Alps, Italy  Biagioni et al., 2016a; Darasun

Downloaded from https://pubs.geoscienceworld.org/eurjmin/article-pdf/30/3/581/4346595/ejm_30_3_0581_0592_biagioni_2710_online.pdf
by University of Arizona user
on 27 September 2018

590

C. Biagioni et al.

Table 9. Comparison between site labels and site occupancy factors (s.o.f.) in marcobaldiite, kirkiite, and jordanite/geocronite isotypes.
Marcobaldiite
Site
Pb1
Pb2
Pb3
Sb4
As5
Pb6
Pb7
Pb8
Pb9
Pb10
Pb11
Sb12
As13
Pb14
Pb15
Pb16
As17
Pb18

s.o.f.
Pb0.85Bi0.15
Pb1.00Pb1.00
Sb1.00As0.63Sb0.37
Pb1.00Pb1.00Pb0.85Bi0.15
Pb0.61Sb0.39
Pb1.00Pb1.00Sb0.98As0.02
As0.91Sb0.09
Pb1.00Pb0.85Bi0.15
Pb0.85Bi0.15
As1.00Pb1.00

Kirkiite
Site
Pb4
Pb3
Pb1
Bi1/As1
As2
Pb2

Pb7
Pb6
As3
Pb5

Jordanite/geocronite
s.o.f.
Pb0.75Bi0.25
Pb1.00Pb1.00Bi0.58/As0.42
As1.00Pb1.00Pb1.00Pb0.5Bi0.5
As1.00Pb1.00Site

s.o.f.

Pb7
Pb8
Pb2/Sb2
Pb1
Pb3
Sb4
As6
Pb5
Pb9
Pb10
As11
Pb12

Pb1.00Pb1.00Pb0.50/Sb0.50
Pb1.00Pb1.00Sb0.61-0.98As0.39-0.02
As1.00-0.75Sb0.00-0.25
Pb1.00Pb1.00Pb1.00As1.00Pb1.00Note: s.o.f. for kirkiite and jordanite/geocronite after Makovicky et al. (2006) and Biagioni et al. (2016a), respectively.

The description of marcobaldiite, characterized by asigniﬁcant Bi content, similar to that reported for Bi-richjordanite from Kirki, poses the question about the role ofthis element in the stabilization of the N = 3.5 homologue.
As a matter of fact, one could note that Bi-rich jordanite
and kirkiite coexist without this intermediate newhomologue and could hypothesize that the three pnictogens As, Sb, and Bi are necessary for the crystallizationof marcobaldiite. However, Moëlo et al. (1990) found Sbrich kirkiite, showing the simultaneous presence of thesethree elements; also in this case, no hints about theoccurrence of marcobaldiite were found. In addition, therecent ﬁnding of the As-rich analogue of marcobaldiite,
arsenmarcobaldiite (Biagioni et al., 2016c), substantiallydevoid of Bi (Bi ≈ 0.30 wt%), seems to discard the
hypothesis that this element could play a key role in theformation of the N = 3.5 homologue.
Fig. 5. Projection in the As-Sb-Bi sub-system of various metalloid
ratios within the jordanite homologous series. Homologues: N = 3,
pink squares (kirkiite); N = 4, yellow triangles (jordanite andgeocronite); N = 3.5, lozenges (marcobaldiite and arsenmarcobaldiite). EPMA: microprobe analysis (light blue lozenges); STR:
crystal structure (dark blue lozenges), with L3: composition of the
kirkiite module (= L3 layer þ intermediate slab), and L4: composition of the geocronite module. Brown circles represent ideal
compositions of marcobaldiite and arsenmarcobaldiite.

ore deposit, Eastern Transbaikalia, Russia  Bryzgalov
et al., 2011). The highest Bi contents were reported byMoëlo et al. (1985) on a sample of jordanite associatedwith type kirkiite, containing up to 4.6 wt% Bi,
corresponding to an ideal formula Pb14As5BiS23 (Fig. 5).
According to Fig. 5, the microprobe analysis of
marcobaldiite agrees with a mixture of geocronite and(Sb,As)-rich kirkiite. According to its crystal structure, thekirkiite-type component is enriched in Sb relatively to As.

5.3. Conditions of formation
The geological history of the baryte þ pyrite ore deposit of
the Pollone mine is very complex and its origin is still
debated (Carmignani et al., 1976; Costagliola et al., 1998).
Recently, Biagioni et al. (2016a) provided new details forunderstanding the evolution of the Pollone ore deposit.
Indeed, the baryte þ pyrite ore bodies have been involvedin the Alpine tectono-metamorphic events affecting therocks belonging to the Apuan Alps metamorphic complex,
indicating a pre-Alpine origin of the mineralization.
During its late stage evolution, the formation of extension
vein systems favored the local remobilization of the orebodies, giving rise to the peculiar sulfosalt assemblages
occurring at the Pollone mine.
The occurrence of Bi is an unusual feature in theframework of the mineralogy of sulfosalts from Apuan
Alps, since up to now very few Bi sulfosalts have been

Downloaded from https://pubs.geoscienceworld.org/eurjmin/article-pdf/30/3/581/4346595/ejm_30_3_0581_0592_biagioni_2710_online.pdf
by University of Arizona user
on 27 September 2018

Marcobaldiite, a new jordanite homologue

identiﬁed from the hydrothermal veins (e.g., Orlandi et al.,2010); at the Pollone mine, small amounts of Bi have beenreported in sterryite (up to 0.26 wt%  Moëlo et al., 2011)
and jordanite/geocronite (up to 0.47 wt%  Biagioni et al.,2016a). According to Moëlo et al. (1985), the elemental
association of Pb, Bi, and As is typical of thermo-chemical
conditions such as high T and weak f(S2) favoring theincorporation of As as an anion in the crystallizing sulﬁdes(e.g., As-bearing pyrite or arsenopyrite). On the contrary, ahigh f(S2) could allow the sulﬁdation of As and its
occurrence in sulfosalts; such a high f(S2) values could beachieved through the interaction between the hydrothermal
solution and a pre-existing sulﬁde ore deposit. At the
Pollone mine, the late recrystallization stage of thebaryte þ pyrite ore could have locally mobilized As underhigh f(S2) conditions, favoring its sulﬁdation to As3þ(Biagioni et al., 2016a), and thus promoting the crystallization of complex Sb-As-(Bi) sulfosalt species. Since it islikely that the stabilization of the N = 3.5 homologue
marcobaldiite is not related to the occurrence of Bi, its
crystallization could be related to small local changes inthermo-chemical conditions as well as Pb/(Sb,As,Bi) ratio,
sufﬁcient to induce the formation of distinct sulfosalts.
However, the question of the stabilization of marcobaldiite remains open, as this phase has not been observedin experimental studies nor in association with jordanite
and kirkiite at Aghios Philippos, Kirki, Greece. Whereas
kirkiite and jordanite have been synthesized (e.g., Walia &Chang, 1973), no hints of the N = 3.5 homologue were
found in experimental studies. However, it should be notedthat some old chemical analyses of jordanite homologues
ﬁt better with the composition Pb12(Sb/As)6S21 than withthat of the N = 4 homologues. As an example, Fisher(1940) reported that the old formula of jordanite was given
Pb4As2S7, corresponding to one third of the ideal
Pb12As6S21 formula of a N = 3.5 homologue. Likely, suchdiscrepancies were related to inaccuracies in chemical
analyses. The composition reported for phase A of Walia& Chang (1973), considered as the synthetic analogue ofkirkiite, can be recalculated, on the basis of 6 (AsþBi)apfu, as Pb11.57(As4.5-3.9Bi1.52.1)S20.57, closer to Pb12(As,Bi)6S21 than Pb10(As,Bi)6S19. In this case, the X-ray
powder diffraction pattern of phase A seems to agree withthat of kirkiite and not with that of marcobaldiite, even if
the diffraction patterns of the jordanite homologues arevery similar.
Owing to such limitations in old chemical analyses andthe similarity in the optical properties as well as in the Xray powder diffraction patterns with other jordanite
homologues, it is likely that the presence of marcobaldiite
in sulfosalt assemblages could have been overlooked. The
best way to detect marcobaldiite is to perform singlecrystal X-ray diffraction studies and systematic andaccurate electron-microprobe analyses.

6. Conclusion
The description of marcobaldiite represents a new case ofhomology in the sulfosalt realm and increases the crystal-591

chemical complexity of the jordanite homologous series.
Makovicky et al. (2006) predicted the possible existenceof N = 1, N = 2, and N = 5 homologues within the jordanite
series. Even if they have not been found yet, the discoveryof the N = 3.5 homologue allows us to hypothesize theexistence of other kinds of combination of the N = 3 andN = 4 octahedral layers, similarly to what happens in thesartorite homologous series (e.g., Moëlo et al., 2008).
This ﬁnding is a further conﬁrmation of the greatmineralogical variability of the sulfosalt assemblages fromthe hydrothermal veins of the Apuan Alps metamorphic
complex. The factors controlling the sulfosalt crystallization are not only related to the occurrence of minor
components (e.g., Ag, Cu, Hg, Tl), ﬁlling speciﬁc atom
positions, and unique f(O2) and f(S2) conditions, promoting
the crystallization of oxysulfosalts or persulfosalts; indeed,
it seems likely that very subtle variations in the Pb/(Sb,As,Bi) atomic ratios in the crystallizing medium can allow theformation of distinct and original mineral species.
Acknowledgments: On occasion of his 80th birthday, wewant to express our gratitude to Stefano Merlino, for his
seminal works on mineral crystal-chemistry and modularity. The paper beneﬁted from the constructive commentsof Emil Makovicky and an anonymous reviewer. This
research received support by MIUR through the SIR 2014
project “THALMIGEN  Thallium: Mineralogy, Geochemistry, and Environmental Hazards”, granted to CB(grant no. RBSI14A1CV). The University Centrum forApplied Geosciences (UCAG) is acknowledged for accessto the E.F. Stumpﬂ electron microprobe laboratory.

References
Baldi, M. (1982): La miniera del Pollone a Valdicastello. Riv.
Mineral. Ital., 6, 46–58.
Biagioni, C., Orlandi, P., Moëlo, Y., Bindi, L. (2014): Leadantimony sulfosalts from Tuscany (Italy). XVI. Carducciite,(AgSb)Pb6(As,Sb)8S20, a new Sb-rich derivative of rathite fromthe Pollone mine, Valdicastello Carducci: occurrence and crystal
structure. Mineral. Mag., 78, 1775–1793.
Biagioni, C., Dini, A., Orlandi, P., Moëlo, Y., Pasero, M., Zaccarini,
F. (2016a): Lead-antimony sulfosalts from Tuscany (Italy). XX.
Members of the jordanite-geocronite series from the Pollone
mine, Valdicastello Carducci: occurrence and crystal structures.
Minerals, 6, 15.
Biagioni, C., Orlandi, P., Moëlo, Y., Stanley, C.J. (2016b): Leadantimony sulfosalts from Tuscany (Italy). XVII. Meerschautite,(Ag, Cu)5.5Pb42.4(Sb, As)45.1S112O0.8, a new expanded derivativeof owyheeite from the Pollone mine, Valdicastello Carducci:
occurrence and crystal structure. Mineral. Mag., 80, 675–690.
Biagioni, C., Merlino, S., Moëlo, Y., Pasero, M., Paar, W.H.,
Vezzoni, S., Zaccarini, F. (2016c): Arsenmarcobaldiite, IMA
2016-045. CNMNC Newsletter No. 33, October 2016, page1138. Mineral. Mag., 80, 1135–1144.
Borodaev, Y.S., Garavelli, A., Kuzmina, O.V., Mozgova, N.N.,
Organova, N.I., Trubkin, N.V., Vurro, F. (1998): Rare sulfosalts
from Vulcano, Aeolian Islands, Italy. I. Se-bearing kirkiite,
Pb10(Bi,As)6(S,Se)19. Can. Mineral., 36, 1105–1114.

Downloaded from https://pubs.geoscienceworld.org/eurjmin/article-pdf/30/3/581/4346595/ejm_30_3_0581_0592_biagioni_2710_online.pdf
by University of Arizona user
on 27 September 2018

592

C. Biagioni et al.

Brese, N.E., O’Keeffe, M. (1991): Bond-valence parameters forsolids. Acta Crystallogr., B47, 192–197.
Bruker, A.X.S. Inc. (2004): APEX 2. Bruker Advanced X-ray
Solutions, Madison, Wisconsin, USA.
Bryzgalov, I.A., Krivitskaya, N.N., Spiridonov, E.M. (2011): Firstﬁnd of the minerals of the jordanite-geocronite-schulzite series
in one deposit (Darasun, Eastern Transbaikalia). Doklady Earth
Sci., 438, 815–818.
Carmignani, L., Kligﬁeld, R. (1990): Crustal extension in thenorthern Apennines: the transition from compression toextension in the Alpi Apuane core complex. Tectonics, 9,1275–1303.
Carmignani, L., Dessau, G., Duchi, G. (1976): Una mineralizzazione sin-tettonica: il giacimento di Valdicastello (Alpi
Apuane). Rapporti fra tettonica e minerogenesi in Toscana.
Boll. Soc. Geol. Ital., 24, 725–758.
Costagliola, P., Benvenuti, M., Lattanzi, P., Tanelli, G. (1998):
Metamorphogenic barite-pyrite-(Pb-Zn-Ag) veins at Pollone,
Apuan Alps, Tuscany: vein geometry, geothermobarometry,ﬂuid inclusions and geochemistry. Mineral. Petrol., 62, 29–60.
Fisher, D.J. (1940): Discussion of “the formula of jordanite”. Am.
Mineral., 25, 297–298.
Frizzo, P., Simone, S. (1995): Diaphorite in the Pollone ore deposit(Apuan Alps, Tuscany, Italy). Eur. J. Mineral., 7, 705–708.
Jambor, J.L. (1969): New lead sulfantimonides from Madoc,
Ontario  Part 3-Syntheses, paragenesis, origin. Can. Mineral.,
9, 505–527.
Kerndt, T. (1845): Über die Krystallform und die chemische
Zusammensetzung des Geo-Kronits von Val di Castello. Ann.
Phys., 141, 302–307.
Kraus, W., Nolze, G. (1996): PowderCell  a program for the
representation and manipulation of crystal structures andcalculation of the resulting X-ray powder patterns. J. Appl.
Crystallogr., 29, 301–303.
Makovicky, E. (1989): Modular classiﬁcation of sulphosalts current status. Deﬁnition and application of homologous series.
N. Jahr. Miner. Abh., 160, 269–297.
Makovicky, E., Balić-Žunić, T., Karanović, L., Poleti, D. (2006):
The crystal structure of kirkiite, Pb10Bi3As3S19. Can. Mineral.,44, 178–188.
Matsushita, Y., Momma, K., Miyawaki, R., Sato, A., Kaise, M.,
Kitazawa, H. (2014): Crystallographic examination of tsugaruite. IMA 2014 Abstract Volume, 331Moëlo, Y., Oudin, E., Makovicky, E., Karup-Møller, S., Pillard, F.,
Bornuat, M., Evanghelou, E. (1985): La kirkiite, Pb10Bi3As3S19,
une nouvelle espèce minérale homologue de la jordanite. Bull.
Minéral., 108, 667–677.

Moëlo, Y., Makovicky, E., Karup- Møller, S., Cervelle, B., Maurel,C. (1990): La lévyclaudite, Pb8Sn7Cu3(Bi,Sb)3S28, une nouvelle
espèce à structure incommensurable, de la série de la cylindrite.
Eur. J. Mineral., 2, 711–723.
Moëlo, Y., Makovicky, E., Mozgova, N.N., Jambor, J.L., Cook, N.,
Pring, A., Paar, W.H., Nickel, E.H., Graeser, S., Karup-Møller,
S., Balić-Žunić, T., Mumme, W.G., Vurro, F., Topa, D., Bindi,
L., Bente, K., Shimizu, M. (2008): Sulfosalt systematics: areview. Report of the sulfosalt sub-committee of the IMA
Commission on Ore Mineralogy. Eur. J. Mineral., 20, 7–46.
Moëlo, Y., Orlandi, P., Guillot-Deudon, C., Biagioni, C., Paar, W.,
Evain, M. (2011): Lead-antimony sulfosalts from Tuscany(Italy). XI. The new mineral species parasterryite, Ag4Pb20(Sb14.5As9.5)Ʃ24S58, and associated sterryite, Cu(Ag,Cu)3Pb19(Sb,As)22(As–As)S56, from the Pollone mine, Tuscany, Italy. Can. Mineral., 49, 623–638.
Orlandi, P., Moëlo, Y., Biagioni, C. (2010): Lead-antimony
sulfosalts from Tuscany (Italy). X. Dadsonite from the Bucadella Vena mine and Bi-rich izoklakeite from the Seravezza
marble quarries. Per. Mineral., 79, 113–121.
Pinto, D., Balić-Žunić, T., Garavelli, A., Garbarino, C., Makovicky,
E., Vurro, F. (2006): First occurrence of close-to-ideal kirkiite at
Vulcano (Aeolian Islands, Italy): chemical data and singlecrystal X-ray study. Eur. J. Mineral., 18, 393–401.
Sheldrick, G.M. (2008): A short history of SHELX. Acta
Crystallogr., A64, 112–122.
— (2015): Crystal structure reﬁnement with SHELXL. Acta
Crystallogr., C71, 3–8.
Shimizu, M., Miyawaki, R., Kato, A., Matsubara, F., Matsuyama, F.,
Kiyota, K. (1998): Tsugaruite, Pb4As2S7, a new mineral species
from the Yunosawa mine, Aomori Prefecture, Japan. Mineral.
Mag., 62, 793–799.
Topa, D., Keutsch, F.N., Makovicky, E., Kolitsch, U., Paar, W.
(2017): Polloneite, a new complex Pb(-Ag)-As-Sb sulfosalt
from the Pollone mine, Apuan Alps, Tuscany, Italy. Mineral.
Mag., 81, 1303–1322.
Walia, D.S., Chang, L.L.Y. (1973): Investigations in the systems
PbS-Sb2S3-As2S3 and PbS-Bi2S3-As2S3. Can. Mineral., 12,
113–119.
Wilson, A.J.C., Ed. (1992): International Tables for X-ray
Crystallography, Volume C: Mathematical, physical andchemical tables. Kluwer Academic, Dordrecht, Netherlands.

Received 4 July 2017
Modiﬁed version received 13 September 2017
Accepted 15 September 2017

Downloaded from https://pubs.geoscienceworld.org/eurjmin/article-pdf/30/3/581/4346595/ejm_30_3_0581_0592_biagioni_2710_online.pdf
by University of Arizona user
on 27 September 2018