Eur. J. Mineral.
2017, 29, 679–688
Published online 1 June 2017

Special issue dedicated toZdeněk Johan

Richardsollyite, TlPbAsS3, a new sulfosalt from the Lengenbach quarry,
Binn Valley, Switzerland
NICOLAS MEISSER1,*, PHILIPPE ROTH2, FABRIZIO NESTOLA3, CRISTIAN BIAGIONI4, LUCA BINDI5 and
MARTIN ROBYR6
1

Musée cantonal de géologie, Université de Lausanne, Anthropole, Dorigny, 1015 Lausanne, Switzerland*Corresponding author, e-mail: nicolas.meisser@unil.ch
2
FGL, Swiss Seismological Service, ETH Zurich, Sonneggstr. 5, 8092 Zurich, Switzerland
3
Dipartimento di Geoscienze, Università di Padova, Via Gradenigo 6, 35131 Padova, Italy
4
Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, 56126 Pisa, Italy
5
Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Via G. La Pira 4, 50121 Firenze, Italy
6
Institut des sciences de la Terre, Université de Lausanne, Géopolis, Dorigny, 1015 Lausanne, Switzerland

Abstract: The new mineral species richardsollyite, TlPbAsS3, was discovered in the Lengenbach quarry, Imfeld, Binn Valley, Canton
Valais, Switzerland, intimately associated with hutchinsonite and baryte. It occurs as grey-black crystals, up to 750 mm, with a metallic
lustre. Under the reﬂected-light microscope, richardsollyite is grey, with bright-red internal reﬂections; anisotropy is distinct, withgreyish-white to bluish rotation tints. Reﬂectance values for the four COM wavelengths are [Rmin, Rmax (%), (l)]: 27.9, 29.8
(471.1 nm); 27.8, 31.0 (548.3 nm); 27.3, 30.8 (586.6 nm); and 27.0, 30.5 (652.3 nm). Electron microprobe analysis gave (in wt%): Tl
34.72(51), Pb 35.45(20), As 12.80(14), Sb 0.04(1), S 16.22(13), total 99.24(47). On thebasis of 6 atoms per formula unit, the chemical
formula is Tl1.001Pb1.008(As1.007Sb0.002)S1.009S2.982. The main diffraction lines [d in A (intensity) hkl] are: 4.23 (80) 1 0 2; 3.875 (70)
2 1 1; 3.762 (100) 2 1 0, 1 2 0; 3.278 (70) 1 0 2; 2.931 (70) 0 2 2; 2.714(70) 1 1 3; and 2.622 (80) 3 1 2. Richardsollyite is monoclinic,

space group P21/c, with a = 8.8925(2), b = 8.4154(2), c = 8.5754(2) A, b = 108.665(3)°, V = 607.98(3) A3, Z = 4. The crystal structure
was solved and reﬁned to R1 = 0.0242 on the basis of 1590 reﬂections with Fo > 4s(Fo). It can be described as formed by (1 0 0) [Pb(AsS3)] layers sandwiching Tlþ cations, and is isostructural with synthetic ABCX3 (A = K, Rb, Cs; B = Eu, Ba; C = As, Sb; X = S, Se)
compounds. The new mineral is named after Richard Harrison Solly (1851–1925) for his outstanding contribution to the knowledge of theLengenbach mineralogy during the ﬁrst ﬂourishing period of Lengenbach investigations, at the beginning of the 20th Century.
Key-words: richardsollyite; new mineral; sulfosalt; lead; thallium; arsenic; crystal structure; Lengenbach; Binn Valley; Switzerland.

(Krenner, 1894). However, the description of hutchinsonite was based on crystal morphology only, similarly a few
years later for hatchite (Solly & Smith, 1912). The
chemical nature of hutchinsonite as a Tl mineral wasestablished by Smith & Prior (1907). The other twentyseven Tl species from Lengenbach were all described in
the modern phase of exploitation and investigation (since1964). A review of the exceptional mineralogy of theLengenbach deposit is given in Roth et al. (2014).
During energy-dispersive X-ray spectrometry (EDXS)
screening of a suite of specimens collected in the
Lengenbach quarry in 2015 by the Lengenbach Research
Association (FGL, the active Lengenbach syndicate),several minerals were set aside for further investigation
owing to their unusual characteristics. One of theseminerals consisted of Pb, Tl, As and S, in a not yet
encountered atomic ratio of approximately 1:1:1:3.
Subsequent X-ray diffraction studies and quantitative
chemical analyses conﬁrmed that this phase was indeed a
new mineral, described here as richardsollyite.

1. Introduction
Thallium displays both chalcophile and lithophile geochemical behaviour, which has resulted in a fascinating
range in the mineralogical diversity of this element.
Among the 63 known mineral species having Tl as an
essential component (as of the end of 2016), 40 belong to
the sulfosalt class. In these minerals, thallium either plays
the same role as Pb2þ, usually replacing it by means ofcoupled substitutions involving Sb3þ, As3þ or Bi3þ, which
replaces neighbouring Pb2þ, or is hosted in channels or
layers, where it assumes a role similar to that of alkali
metals, e.g. Kþ (Makovicky, 2005).
The most important locality for the study of Tl sulfosalts is certainly the Lengenbach quarry, Imfeld, Binn
Valley, Switzerland, the type locality of 21 Tl-bearing
mineral species. In 1905, hutchinsonite (Solly, 1905) was
the ﬁrst Tl mineral to be described from this locality and it
represented only the third known Tl mineral worldwide
after crookesite (Nordenskiöld, 1866) and lorándite
eschweizerbart_xxx

DOI: 10.1127/ejm/2017/0029-2649

0935-1221/17/0029-2649 $ 4.50

© 2017 E. Schweizerbart’sche Verlagsbuchhandlung, D-70176 Stuttgart

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N. Meisser et al.

Table 1. Species constituting the mineral assemblage of Lengenbach quarry metadolostone Ribbon 1, Zone 1, in whichrichardsollyite was found. Tl minerals are marked in bold.

The mineral and its name were approved by the
CNMNC-IMA (2016-043). The holotype specimen ofrichardsollyite is deposited in the Mineralogical Collection of the Musée cantonal de géologie, University of
Lausanne, Anthropole, Dorigny, 1015 Lausanne,
Switzerland, with catalogue number MGL no. 080126.
The name honours Richard Harrison Solly (1851–
1925), a British autodidact who carefully described,
between 1901 and 1912, eight new mineral species forLengenbach. He can be considered as the most successful
scientist of the ﬁrst ﬂourishing period of Lengenbach
investigations, at the beginning of the 20th Century.
However, whereas several scientists of this period havebeen honoured by giving their name to a Lengenbachmineral (H. Baumhauer, A. Dufrénoy, F.H. Hatch, A.
Hutchinson, H. Jordan, G.D. Liveing, J.E. Marr, G. vom
Rath, W. Sartorius von Walterhausen, G. Seligmann,
G.F.H. Smith, and C.O. Trechmann), Solly is missing inthis list. In an effort to assign names to insufﬁciently
characterized minerals, Gagarin & Cuomo (1949), without
any investigation and based only on literature data, did
give the name “sollyite” to a ﬁbrous sulfosalt from
Lengenbach, later discredited by Nowacki et al. (1960) as
a mixture of two to three different minerals. This happened
more than 50 years ago and the name “sollyite” is now
available according to the IMA rules (Nickel & Grice,1998). However, to avoid any confusion with samples
previously labelled “sollyite” in old collections, we chosethe name richardsollyite for the new mineral species.
This paper reports the description of the new mineralrichardsollyite and its crystal structure, together with a
discussion of its relationships with a few related synthetic
compounds.

“Adularia” and “hyalophane”
Aktashite
Argentobaumhauerite
Argentodufrénoysite
Argentoliveingite
Arsenic
BaryteBaumhauerite
Bernardite
Canﬁeldite (Te-rich)
Cerussite
Cofﬁnite
Covellite
Dolomite
DraviteDufrénoysite
Edenharterite
Erniggliite
Ferrostalderite
GalenaHatchite

Hutchinsonite
Hydrocerussite
Incomsartorite
ImhoﬁteJentschite
Jordanite
Kaolinite
Lengenbachite
Liveingite
MarriteMuscovite
Nowackiite
Orpiment
Pararealgar
Parapierrotite
Picotpaulite
Proustite
PyriteQuadratite
QuartzRalphcannonite

RathiteRealgarRichardsollyite
Routhierite (?)
RutileSartorite
Seligmannite
SilverSinnerite
Smithite
Sphalerite
Stalderite
Tennantite
Thalcusite
ThoriteTochilinite
Trechmannite
Uraninite
Wallisite
Wurtzite
Xanthoconite

et al., 2014). The presence of a hydrothermal aqueous ﬂuid
during and after the crystallization of the sulphide melt
was interpreted to be responsible for the re-crystallisationof dolomite and baryte (Hofmann et al., 1993), which areclosely associated to richardsollyite in vugs.
The mineralization occurs in the uppermost part of a
240 m thick metadolostone sequence, 180–200 m above its
base, close to the contact with the Jurassic to Lower
Cretaceous metapelite locally called “Bündnerschiefer”.
The mineralization in the quarry can be subdivided into
four different types according to geometric criteria(Hofmann & Knill, 1996). Using different spatial andgeochemical criteria, Graeser et al. (2008) distinguishedﬁve major, bedding-parallel zones. Richardsollyite, like all
the recently described new mineral species, occurs intheir realgar-bearing, As- and Tl-rich “Zone 1”.
The FGL collected the studied specimen (L-15-6763)
in 2015 on level 4. In this extraction area, Zone 1 ofGraeser et al. (2008) can be further subdivided into
isolated, bedding-parallel, mineralized metadolostone
ribbons and lenses spaced approximately 1 m apart.
Richardsollyite was found in “Ribbon 1”, a particularlyinteresting and well-documented, realgar-rich body. It
measured 4 m  2 m, with a maximum thickness of 0.5 m,
and was found to contain a high concentration of rare Tlrich species. Table 1 summarizes the minerals identiﬁedin that volume of metadolostone. The body is sharply
separated from the adjacent, poorly mineralized, metadolostone layers. Another mineralized metadolostone
ribbon, mined further to the south in the same period, wasfound to be almost completely Tl-free, even if its realgar
concentration – and therefore its apparent As concentration, commonly thought to be correlated to and therefore
indicative of Tl – was even higher there than in Ribbon 1.

2. Occurrence and mineral description
2.1. Occurrence and physical properties
Richardsollyite was collected in cavities of the Triassic
metadolostone exposed in the Lengenbach quarry, Imfeld,
Binn Valley, Canton Valais, Switzerland (46°210 5400 N,
8°130 1500 E). The mineralized Triassic metadolostone
exploited at this locality occurs at the front of the Monte
Leone Nappe, in the Penninic domain of the Alps. The
Lengenbach deposit has been interpreted to have formedby remobilization of a pre-existing carbonate-hosted Pb–
Zn–Ag–Cu–Cd–Tl–As ore deposit and subsequent crystallization from sulphide melt as well as hydrothermal
solutions, during Alpine metamorphism under upper
greenschist- to lower amphibolite-facies conditions(Hofmann, 1994). This sulphide melt underwent fractional
crystallization of sulfosalts such as richardsollyite andassociated hutchinsonite, dufrénoysite, wallisite–hatchite
series and realgar, which resulted in the enrichment of As
and Tl, and the depletion of Pb in the remaining melt
fractions. This is shown by compositional trends measured
in melt inclusions (Hofmann, 1994), by the presence ofmore As- and Tl-enriched mineral species in late-stage
vugs and veins, and by Tl-isotope fractionation (Hettmanneschweizerbart_xxx

Richardsollyite, a new thallium sulfosalt

681

Fig. 3. Backscattered electron image of polished grain ofrichardsollyite extracted from holotype specimen MGL no.
080126 (L-15-6763). Note the vesicular appearance and thechemical homogeneity.
Fig. 1. Metallic grey-black richardsollyite crystals with striated andcurved faces have grown on cherry-red hutchinsonite. Associatedminerals are Tl-bearing dufrénoysite, in tiny ﬁbrous red-brown
needles, orange-red realgar, ﬁne-grained colourless dolomite, andgemmy colourless baryte. Holotype specimen, MGL no. 080126 (L15-6763).

In plane-polarized incident light, richardsollyite is grey
in colour. Under crossed polarisers, it is distinctly
anisotropic, with greyish to bluish rotation tints. Internal
reﬂections are bright red. Reﬂectance measurements werecarried out at the Dipartimento di Scienze della Terra,
Università degli Studi di Firenze, using a MPM-200 Zeiss
microphotometer equipped with a MSP-20 systemprocessor 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 formeasurements (471.1, 548.3, 586.6, and 652.3 nm).
Readings were taken for sample and standard (SiC)
maintained under the same focus conditions. The diameterof the circular measuring area was 0.1 mm. Reﬂectancepercentages are [Rmin, Rmax (l in nm)]: 27.9, 29.8 (471.1);
27.8, 31.0 (548.3); 27.3, 30.8 (586.6); and 27.0, 30.5
(652.3). All measurements were done in air.
On the holotype specimen MGL no. 080126 (L-156763), richardsollyite is closely associated with hutchinsonite and baryte; other minerals occurring in the same
specimen are Tl-bearing dufrénoysite, realgar, pyrite, anddolomite.
Richardsollyite was identiﬁed on a second FGL
specimen (L-15-6558) from Ribbon 1. Although its
EDXS spectrum indicates the absence of detectable traceelements (besides Sb), the physical appearance isdifferent: dark copper-red stacks of tabular to lamellar
crystals (Fig. 2) associated with an intermediate memberof the hatchite–wallisite solid solution isotypic pair(corresponding to the composition hatchite61wallisite39),
hutchinsonite, probable sartorite, realgar and dolomite.

Fig. 2. Backscattered electron image of the second specimen ofrichardsollyite. It shows stacks of lamellar crystals on dolomite.
Oblique terminal faces are discernible in the top left aggregate.
Sample specimen no. L-15-6558.

In the specimen studied, richardsollyite forms greyblack euhedral crystals, up to 750 mm across (Fig. 1). The
streak is black and the lustre is metallic; it is brittle, with
uneven fracture and without any visible cleavage surface.
Micro-indentation measurements, carried out with a
VHN load of 25 g, give a mean value of 188 kg/mm2(range 170–203), corresponding to a Mohs hardness of∼3–3.5. Owing to the rarity and size of richardsollyite, nograin suitable for density measurement was available.
The calculated density, based on the empirical formula, is6.392 g/cm3; by using the ideal formula, the calculated
density is 6.365 g/cm3.

2.2. Chemical data
A preliminary chemical analysis performed by energydispersive spectrometry on a portion of the grain used forthe crystal structure study (Fig. 3) did not indicate thepresence of elements with Z > 9 other than Tl, Pb, As and
S. In addition, back-scattered electron images showed thecompositional homogeneity of the studied grain.
eschweizerbart_xxx

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N. Meisser et al.

Table 2. Electron microprobe analysis of richardsollyite: chemicalcomposition as wt% (average of 9 spot analyses) and chemical
formula (in atoms per formula unit, apfu) on the basis of 6 apfu.
Element

wt%

Range

e.s.d.

apfu

Tl
Pb
As
Sb
S
Total
Ev

34.72
35.45
12.8
0.04
16.22
99.23

33.92–35.32
35.07–35.69
12.64–13.12
0.02–0.07
16.02–16.44
98.77–99.70

0.51
0.2
0.14
0.01
0.13
0.47

1.001
1.008
1.007
0.002
2.982

Sb0.002)S1.009S2.982. The ideal formula is TlPbAsS3, which
requires (in wt%) Tl 35.08, Pb 35.56, As 12.86, S 16.51,
total 100.00.
2.3. Crystallography
The X-ray powder diffraction pattern of richardsollyite
was collected using a 114.6 mm Gandolﬁ camera with Niﬁltered Cu Ka radiation. Elemental Si was used as internal
standard. The observed pattern is reported in Table 3,
where it is compared with that calculated using thesoftware PowderCell (Kraus & Nolze, 1996) using thestructural model described below. Owing to the multiple
contributions for the majority of the observed reﬂections,the unit-cell parameters were not reﬁned from X-ray
powder diffraction data.
Single-crystal X-ray intensity data collection was
carried out at the Dipartimento di Geoscienze, Università
di Padova, using a Supernova (Agilent Technologies)
diffractometer equipped with the Mova micro-source (spotsize 0.120 mm, Mo Ka) and assembled with a Pilatus
200 K detector (Dectris). A total of 1775 unique reﬂections
were collected.
X-ray diffraction intensity data were integrated andcorrected for standard Lorentz-polarization factors with
the CrysAlis RED (Oxford Diffraction, 2006) software
package. Absorption correction was performed using the
program ABSPACK in CrysAlis RED (Oxford Diffraction,2006). The statistical tests on the distribution of |E| values(|E21| = 0.867) and systematic absences suggested thespace group symmetry P21/c. The reﬁned unit-cellparameters
are a = 8.8925(2), b = 8.4154(2),c = 8.5754
(2) A, b = 108.665(3)°, V = 607.98(3) A3, Z = 4. The a:b:c
ratio is 1.0567:1:1.0190.
The structure of richardsollyite was solved by direct
methods using Shelxs-97 and then reﬁned through Shelxl2014 (Sheldrick, 2015). Scattering curves for neutral
atoms were taken from the International Tables for
Crystallography (Wilson, 1992). After having located theheavier atoms (Pb and Tl sites), the remaining atom
positions were found through successive differenceFourier maps. In the crystal structure of richardsollyite,
three cation sites and three anion positions occur.
Initially, owing to the similar scattering factors of Pb
and Tl, only the scattering curve of the former was used.
The site occupation factor (s.o.f.) of the three independent
cation positions were reﬁned using the following curves:
Pb vs. □ for Me1 and Me2 sites, and As vs. □ for As site.
All cation positions were found fully occupied and theirs.o.f. were ﬁxed to 1. Taking into account the bondvalence balance, calculated using the bond-parameters
given by Brese & O’Keeffe (1991), Me1 and Me2
sites were assigned to Tl and Pb, respectively. Afterseveral cycles of anisotropic reﬁnement, the agreement
factor R1 converged to 0.0242 for 1590 reﬂections with
Fo > 4s(Fo).
Details of the data collection and crystal structure
reﬁnement are given in Table 4.

1.3



Relative error on the valence equilibrium (%), calculated as
100  [S(valþ)  S(val)]/S(val).

Table 3. X-ray powder  diffraction data for richardsollyite.
Intensities and dhkl (in A) were calculated using the software
PowderCell 2.3 (Kraus & Nolze, 1996) on the basis of the structuralmodel given in Table 5. The seven strongest reﬂections are given in
bold. Only reﬂections with Icalc ≥ 10 were reported.
Iobs dobs

80

4.23

70

3.875

100 3.762
40
70

3.633
3.278

30
30
70
50

3.063
2.983
2.931
2.805

70

2.714

60

2.663

80

2.622

Icalc

dcalc

hkl

 11
51
14
93
 35
100
64
36
49
94
15
34
28
92
 54
23
79
 17
58
22
 74
62
17

5.85
4.23
4.21
3.866
3.777
3.767
3.764
3.736
3.619
3.272
3.243
3.050
2.982
2.922
2.795
2.711
2.707
2.664
2.661
2.652
2.622
2.611
2.608

011
1 02
200
2 11
1 12
210
120
021
1 21
102
121
112
1 22
022
3 11
2 22
1 13
310
130
031
3 12
221
1 31

Iobs dobs
30
40
20
20

2.462
2.332
2.204
2.122

30

2.056

30

2.045

20
20

1.967
1.961

30

1.895

Icalc

dcalc

hkl

16
14
28
25
12
 16
14
 14
22
11
17
18
17
11
22
19
12
15
12
11
13
12
17

2.576
2.457
2.330
2.200
2.113
2.063
2.061
2.050
2.043
2.041
1.985
1.970
1.962
1.944
1.894
1.885
1.802
1.770
1.719
1.715
1.661
1.638
1.614

2 13
131
311
2 32
2 04
123
3 23
2 14
410
140
330
312
4 21
141
2 41
232
114
5 02
4 32
3 41
043
1 51
3 34

Quantitative chemical analyses of richardsollyite werecarried out at Institut des sciences de la Terre, Universitéde Lausanne, using a JEOL 8200 electron microprobe
operating in wavelength-dispersive mode. Experimental
conditions were: accelerating voltage 20 kV, beam current
40 nA, focused electron beam. Counting times were 20 s
for peak and 10 s for background. Standards (element,
emission line) were: lorándite (Tl Ma, As La), PbS (Pb
Ma, S Ka), and Sb2S3 (Sb La). Fe, Cu, Zn, Ag, and Hg
were sought but found to be below the detection limit(0.02 wt%).
Electron microprobe data for richardsollyite are
given in Table 2. On the basis of 6 atoms per formula
unit (apfu), the chemical formula is Tl1.001Pb1.008(As1.007
eschweizerbart_xxx

Richardsollyite, a new thallium sulfosalt

Table 4. Crystal data and summary of parameters describing datacollection and reﬁnement for richardsollyite.
Crystal data
Crystal size (mm3)Cell setting, space groupa (A )
)
b (A

c (A)
b (°)V (A3)Z
Data collection and reﬁnement

Radiation, wavelength (A)Temperature (K)2umax (°)
Measured reﬂections
Unique reﬂections
Reﬂections with Fo > 4s(Fo)Rint
Rs
Range of h, k, l
R [Fo > 4s(Fo)]R (all data)wR (on F2)
GooF
No. of reﬁned parameters
Maximum and minimum
residual peak (e, A3)683

the undersaturation at the Pb site could also be related toexperimental errors or to the inadequacy of the ionicmodel used to describe this covalent compound. Arsenic
displays a typical trigonal pyramidal
coordination, with
average 〈As–Si distance of 2.258 A and distances ranging
between 2.246(2) and 2.274(2) A. The corresponding
bond-valence sum is 3.01 v.u.
Sulfur atoms display different bond environments. S1
is ﬁve-fold coordinated, with a square pyramidal
coordination. The As site occupies the pyramidal apex,
with a short 2.246(2) A distance, whereas the base has two
Pb and two
Tl atoms, at distances ranging from 3.004(2) to
3.115(2) A . A sixth bond involves a Tl atom located at
3.570(2) A, giving rise to a distorted octahedral coordination. The bond-valence sum at the S1 atom is 2.20 v.u. A
similar bonding environment is shown by the S2 site. In
this case, S2 is bonded to As (at 2.274 A) and four Pb
atoms,
at distances ranging between 3.040(2) and 3.229
(2) A. The coordination is completed by a sixth Tl atom at
3.433(2) A. The bond-valence sum, at the S2 site, is1.91 v.u. Finally, S3 is coordinated by As, two Pb, and two
Tl atoms; an additional Tl atom is at a very long distance,
taking into
3.837(2) A. The bond-valence sum, calculated
account Me–S distances shorter than 3.60 A, is 1.92 v.u.

0.200  0.100  0.060
Monoclinic, P21/c
8.8925(2)8.4154(2)8.5754(2)108.665(3)607.98(3)4Mo Ka, l = 0.71073
293
60.06
16596
1775
1590
0.05760.028012  h  12
11  k  11
12  l  12
0.02420.02920.05221.051
56

2.56 (at 0.73 A fromTl)
1.94 (at 0.66 A from Tl)

3.2. Crystal structure of richardsollyite
The crystal structure of richardsollyite can be described ashaving (1 0 0) [Pb(AsS3)] layers sandwiching Tlþ cations(Fig. 4a, b).
The PbS8 polyhedra share rectangular faces and edges
to form chains along b; the sharing of rectangularfaces
gives rise to Pb–Pb distances of 3.744(1) A. These chainsare connected along c through sharing the triangular facesof the trigonal prismatic coordination polyhedra of Pb. The
AsS3 trigonal pyramids decorate the polyhedral layer
formed by Pb atoms on both sides, giving rise to the (1 0 0)
[Pb(AsS3)] layers. These layers are connected along[1 0 0] through Tl–S bonds.
This kind of structure is new for natural sulfosalts,
whereas it is isostructural with a few synthetic compounds.

3. Crystal structure description
Atomic coordinates and displacement parameters areshown in Table 5, whereas Table 6 gives selected bonddistances.
3.1. Atom coordination and bond-valence sum
The crystal structure of richardsollyite has three independent cation sites, i.e. Pb, Tl, and As, and three S sites. All
these sites are located at the general 4e position. The Pbsite has a distorted bicapped trigonal prismatic coordination, with bond distances ranging between 2.906(2)and
3.451(2) A, with an average bond distance of 3.122 A. The
bond-valence sum, at the Pb site, is 1.85 valence unit (v.u.).
Thallium exhibits seven-foldcoordination, with anadditional ligand at 3.837(2) A, giving rise to a distorted
bicapped trigonal prism. The seven short Tl–S distances
range between 3.111(2)and 3.570(2) A, with average
〈Tl–Si of 3.333 A. The bond-valence sum is 1.21 v.u. The
slight oversaturation at the Tl site, coupled with the slightunderbonding at the Pb position, could be interpreted as
due to a partial substitution of Tl at the Pb site and viceversa. Actually, Biagioni et al. (2014a) pointed out that thebond parameter for the pair (Tl,S) tabulated by Brese &O’Keeffe (1991) is likely  overestimated, suggesting theuse of a value around 2.55 A. By using this value, the bondvalence sum at the Tl is lowered to 0.98 v.u. Consequently,

4. Discussion
4.1. Richardsollyite in the framework of lead–thallium sulfosalts
Richardsollyite is the ﬁfteenth natural Tl–Pb sulfosalt andthe sixth having a (Tl/Pb) atomic ratio of 1 (Table 7). It is
impressive that eleven of these have their type locality in
Lengenbach: hutchinsonite (Solly, 1905), edenharterite(Graeser & Schwander, 1992), jentschite (Graeser &Edenharter, 1997), the isotypic pair hatchite–wallisite(Solly & Smith, 1912; Nowacki, 1965), dalnegroite(Nestola et al., 2009), and the recently deﬁned minerals
enneasartorite, hendekasartorite, heptasartorite, andincomsartorite (Topa et al., 2016b, 2017a, this issue).
The other four were ﬁrst described from Jas Roux, HautesAlpes, France (chabournéite – Johan et al., 1981; écrinsite
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Table 5. Atomic fractional coordinates and displacement parameters (A2) for richardsollyite.
Site

x

y

z

U11

U22

U33

U23

U13

U12

Ueq

Tl
Pb
As
S1
S2
S3

0.41635(3)0.91460(3)0.75779(7)0.7371(2)0.0211(2)0.6498(2)0.41732(4)0.29496(3)0.55112(7)0.6012(2)0.4913(2)0.3060(2)0.78403(4)0.98230(3)0.62970(7)0.8792(2)0.7176(2)0.5876(2)0.0291(2)0.0262(1)0.0230(3)0.0219(7)0.0182(7)0.0214(8)0.0343(2)0.0186(1)0.0148(3)0.0191(7)0.0242(8)0.0233(8)0.0336(2)0.0289(1)0.0169(3)0.0232(7)0.0182(7)0.0409(10)0.0049(1)0.0036(1)0.0041(2)0.0051(6)0.0044(6)0.0151(7)0.0081(1)0.0108(1)0.0046(2)0.0079(6)0.0055(5)0.0124(7)0.0060(1)0.0008(1)0.0026(2)0.0015(6)0.0037(6)0.0057(6)0.0328(1)0.0241(1)0.0186(1)0.0212(3)0.0203(3)0.0280(4)Table 6. Selected bond distances (in A) for richardsollyite.
Tl –S1
–S1
–S3
–S3
–S2
–S3
–S1

3.111(2) Pb –S3
3.115(2)–S1
3.203(2)–S2
3.340(2)–S1
3.433(2)–S23.560(2)–S2
3.570(2)–S2–S3Mean 3.333
Mean

2.906(2) As –S1
3.004(2)–S3
3.040(2)–S2
3.068(2)Mean
3.090(2)3.186(2)3.229(2)3.451(2)3.122

2.246(2)2.255(2)2.274(2)2.258– Topa et al., 2017b), and from the Monte Arsiccio mine,
Tuscany, Italy (boscardinite – Orlandi et al., 2012;
protochabournéite – Orlandi et al., 2013). Among Pb–
Tl sulfosalts, richardsollyite is richest in (Pb þ Tl), with a[(Pb þ Tl)/As] atomic ratio of 2; in the other known
sulfosalts, this ratio is 1.
In sulfosalt systematics, two different crystal-chemical
behaviours of Tl have been observed in Pb–Tl sulfosalts(Moëlo et al., 2008):
i) Tlþ replacing Pb2þ, both as a minor component or as an
essential constituent. In this case, the introduction ofTlþ is related to an increase of Me3þ (usually As or Sb)
content, according to the substitution mechanismTlþ þ Me3þ = 2Pb2þ;ii) Tl and Pb occurring at different positions.

Fig. 4. Crystal structure of richardsollyite as seen down b (a) and c(b). Light blue polyhedra represent the Pb site. Tl and As sites are
represented as grey and red ball-and-sticks, respectively and S asyellow circles. For sake of comparison, the crystal structure ofchristite (c), as seen down c, is shown. Same symbols as in (a) and(b) for Tl, As, and S sites; green polyhedra represent the Hg site.

Case i is represented by minerals derived from Tl-free,Pb end-members. As an example, boscardinite is the Tl–Sb
homeotype of the pure Pb–As sulfosalt baumhauerite(Orlandi et al., 2012; Biagioni & Moëlo, 2017a). In thismineral, thallium occurs in pure Tl or mixed (Tl/Pb)
positions, with a pure Tl site having a tricapped trigonal
prismatic coordination.
The average 〈Tl–Si distance is
3.36–3.37 A. Écrinsite, a new mineral species recently
described by Topa et al. (2017b), displays similar features
as the new sartorite homeotypes (Topa et al., 2017a). A
signiﬁcant Tl–Pb substitution is also shown by members of
the chabournéite series (chabournéite, dalnegroite, andprotochabournéite), with Tl usually occurring in bonding
environments similar to those observed in boscardinite.
The occurrence of non-negligible amounts of Tl in Pb
sulfosalts is well-known, having been reported indufrénoysite and rathite (Laroussi et al., 1989; Berlepsch
et al., 2002; Moëlo et al., 2008), as well as, more recently,
in the oxy-sulfosalts rouxelite and chovanite (Biagioni
et al., 2014b; Biagioni & Moëlo, 2017b).

Case ii is well exempliﬁed by members of thehutchinsonite merotypic series hutchinsonite, edenharterite,
and jentschite (e.g. Makovicky, 1997). Indeed, Tl and Pb are
partitioned into different sites, with different average bonddistances. In the eponymous mineral hutchinsonite,
Pb is
seven-fold coordinated, with 〈Pb–Si of 3.06 A whereas Tl
has seven short Tl–S distances andthree longer ones, with
average 〈Tl–Si distances of 3.45 A (Matsushita & Takéuchi,
1994). In the pair edenharterite–jentschite,
Berlepsch (1996)
gave 〈Pb–Si of 3.07–3.08 A and 〈Tl–Si of 3.31 A. Bothelements have seven shorter (= stronger) Me–S bonds, but Tl
displays two additional longer (= weaker) bonds. The crystal
structures of the isotypic pair hatchite–wallisite werestudied by Marumo & Nowacki (1967) and by Takéuchi
& Ohmasa (1968). Later, Boiocchi & Callegari (2003)
studied an intermediate member in the hatchite–wallisite
solid solution. Also in these minerals Pb and Tl arepartitioned in two different eight-fold coordinated sites,
havingaverage 〈Pb–Si and 〈Tl–Si distances of 3.10 and
3.44 A (Boiocchi & Callegari, 2003), respectively.
eschweizerbart_xxx

Richardsollyite, a new thallium sulfosalt

685

Table 7. Unit-cell parameters, space group and chemical formula of lead–thallium sulfosalt species.


Mineral species

a (A)

b (A)

c (A)

a (°)

b (°)

g (°)

s.g.

Chemical formula

Ref.

Boscardinite
Chabournéite
Dalnegroite
Écrinsite
Edenharterite
Enneasartorite
Hatchite
Hendekasartorite
Heptasartorite
Hutchinsonite
Incomsartorite
Jentschite
Protochabournéite
Richardsollyite
Wallisite

8.09
8.52
16.22
8.08
15.48
37.61
8.04
31.81
29.27
10.79
45.99
8.10
8.15
8.89
7.98

8.76
42.46
42.55
8.53
47.60
7.88
9.17
7.89
7.88
35.39
7.87
23.92
8.72
8.42
8.97

22.50
16.29
8.56
22.61
5.85
20.07
7.81
28.56
20.13
8.14
58.67
5.89
21.58
8.58
7.76

90.9
83.4
95.7
90.2
90
90
105.2
90
90
90
90
90
85.2
90
106.1

97.2
91.0
90.2
97.2
90
101.9
113.6
99.0
102.1
90
90.15
108.1
96.9
108.7
114.5

90.8
84.3
96.4
90.8
90
90
64.8
90
90
90
90
90
88.6
90
65.5

P1
P1
P1
P1
Fdd2
P21/b
P1
P21/b
P21/b
Pbca
P21/n
P21/n
P1
P21/c
P1

TlPb4(Sb,As)9S18
Tl2Pb(Sb,As)10S17
Tl2Pb(As,Sb)10S17
AgTl3Pb4As11S9S36
TlPbAs3S6
Tl6Pb32As70S140
AgTlPbAs2S5
Tl2Pb48As82S172
Tl7Pb22As55S108
TlPbAs5S9
Tl6Pb144As246S516
TlPbAs2SbS6
Tl2Pb(Sb,As)10S17
TlPbAsS3
CuTlPbAs2S5

[1]
[2]
[3]
[4]
[5]
[6]
[7]
[6]
[6]
[8]
[9]
[5]
[10]
[11]
[12]

[1] Orlandi et al. (2012); [2] Biagioni et al. (2015); [3] Bindi et al. (2010); [4] Topa et al. (2017b); [5] Berlepsch (1996); [6] Topa et al.
(2017a); [7] Marumo & Nowacki (1967); [8] Matsushita & Takéuchi (1994); [9] Topa et al. (2016b); [10] Orlandi et al. (2013); [11] this work;[12] Takéuchi & Ohmasa (1968).

in the [B2þ(C3þS3)] sheet of christite, the lone-electronpair activity of Pb2þ gives rise to an asymmetriccoordination without any symmetry plane parallel to thesheets in richardsollyite.
Synthetic TlPbAsS3 was reported by Cai (1984), but its
crystal structure was not solved. In contrast, Balić-Žunić &Bente (1995) studied synthetic TlPbSbS3 and solved its
crystal structure on the basis of X-ray powder diffraction
data. This synthetic compound occurs in two polymorphs,
i.e. a high-T orthorhombic Cmcm phase and a low-T
monoclinic P21/c dimorph. The latter has the unit-cellparameters a = 4.17, b = 4.29, c = 12.16 A, b = 105.5°,
V = 209.4 A3. Its crystal structure is characterized by tightly
bonded double-layers of atoms, with deformed semioctahedral coordinations. The atomic double-layers arestacked along c through longer Me–S bonds. This structure
could be an average structure, as indicated by the cation
disorder, with Tl, Pb, and Sb occupying the same site. It is
likely that these cations would be ordered in the true
structure, as observed for Tl, Pb, and As in richardsollyite.
Thus, the crystal structure displayed by richardsollyite
is new among sulfosalts, but it has been observed in somesynthetic alkali sulfosalts (Table 8). Indeed, Bera &Kanatzidis (2008) synthesized three Eu compounds inmolten alkali-metal polysulphide salts, having thecompositions KEuAsS3, RbEuAsS3, and CsEuAsS3.
These compounds display the same structure type asrichardsollyite, i.e. (1 0 0) [Eu(AsS3)] layers sandwiching Aþ ions, where A = (K, Rb, Cs).
The unit-cell volume of richardsollyite
is close to that of
KEuAsS3, i.e. 607.98 vs. 608.98 A3. In order to compare
their observed and theoretical unit-cell volumes, these twocompounds can be considered as mixtures of the simple
sulphides Tl2S þ Pb2S2 þ As2S3 and K2S þ Eu2S2 þ As2S3,= 86.13 A3) is larger
respectively. The volume of Tl2S (V
3than that  of K2S (V = 79.36 A ), whereas Pb2S2(V = 104.48 A 3) is slightly smaller than  Eu2S2(V = 106.43 A3). The volume of As2S3 is 116.92 A3. Thus,

Table 8. Synthetic isotypic analogues of richardsollyite.
Compounda (A) b (A) c (A) b (°)



V (A3) s.g.

Ref.

Richardsollyite 8.892 8.415 8.575 108.66 607.98 P21/c [1]KEuAsS3
8.831 8.346 8.622 106.59 608.98 P21/c [2]9.080 8.367 8.675 105.84 633.99 P21/c [2]RbEuAsS3
9.395 8.441 8.770 105.12 671.40 P21/c [2]CsEuAsS3
9.369 9.049 9.247 108.23 744.60 P21/c [3]KBaAsSe3
KBaSbSe3
9.386 9.199 9.369 108.25 768.30 P21/c [3][1] This work; [2] Bera & Kanatzidis (2008); [3] Yin et al. (2014).

Richardsollyite represents a new example among Pb–Tl
sulfosalts of crystal-structure partitioning of these two
metals.
4.2. Relationships with natural AþB2þC3þS3
minerals and synthetic analogues
Richardsollyite is a new example of AþB2þC3þS3
compound among natural sulfosalts. Balić-Žunić & Bente(1995) stressed the role of the A cation in controlling thetype of crystal structure shown by these ternarycompounds. Among the ﬁfteen known sulfosalts havingsuch a formula, the Aþ cation is represented by Tl(christite, richardsollyite), Cu (members of the isotypicseries of bournonite and of mückeite, as well as aikinite),and Ag (in the freislebenite series and the related isotypicpair manganoquadratite–quadratite, as well as in lafﬁttite).
Christite, TlHgAsS3, the only other ternary sulfosalt withTl as the Aþ cation, shows some similarity withrichardsollyite. Indeed, they have a similar unit-cellvolume, i.e. 601 and 608 A3 in christite and richardsollyite,
respectively, and a similar atomic stacking along b ofchristite and a of richardsollyite (Fig. 4c). Brown &Dickson (1976) described the crystal structure of christite
as formed by two-dimensional [Hg(AsS3)] sheets,
bonded together by Tl–S bonds. Whereas the Hgcoordination induces the presence of a symmetry planeeschweizerbart_xxx

686

N. Meisser et al.

described from only one locality, i.e. the Oktyabr’skoeCu–Ni deposit in Norilsk, eastern Siberia, Russia. A third
compound, “Cu–djerﬁsherite” has been described, but notformally approved, as a different mineral species(Azarova et al., 2006). In addition, Cl-poor analoguesof these minerals have been reported (Barkov et al.,1997). The crystal structure of djerﬁsherite (Dmitrieva
et al., 1979) can be considered a derivative of thepentlandite structure. Potassium, as well as Tl, is hosted
within structural channels. A short review of the crystal
structures of this mineral group is given in Makovicky(2005).
Among sulfosalts, thallium–alkali substitutions are
known in the homeotypic pair gillulyite–ambrinoite, withthe compositions Tl2(As,Sb)8S13 and (K,NH4)2(As,Sb)8S13,
respectively. Their crystal structures show [(As,Sb)8S13]2
slabs, with Tl and K (the latter being coordinated also by
H2O groups) hosted within inter-slab spaces (Makovicky &Balić-Žunić, 1999; Biagioni et al., 2011).
Galkhaite, ideally (Hg5Cu)CsAs4S12 (Biagioni et al.,2014c), is the only Cs sulfosalt known to date; it is an
example of a cage-like chalcogenide, with Cs hosted in the
twelve-fold coordinated cavities of a tetrahedrite-likeskeleton (Makovicky, 2005). In a few cases, Tl has beenfound as a minor component replacing Cs, but Chen &Szyma
nski (1981) reported chemical analyses with Tl > Cs,
which pointed to the possible existence of a Tl-dominantanalogue. Such a Tl analogue of galkhaite was recently
approved as vorontsovite, (Hg5Cu)TlAs4S12 (Kasatkin
et al., 2016).
Other Tl–K substitutions in minerals are known, e.g. inchalcothallite, Tl2(Cu,Fe)6SbS4, containing 0.8 wt% K(Makovicky et al., 1980).
Taking into account such a widespread Tl–K substitution in chalcogenides, the description of richardsollyite
and its relationships with synthetic analogues allow us topredict the existence of natural alkali analogues, e.g.
KPbAsS3, especially in hyperalkaline geochemical environments, such as, igneous alkaline rocks and marine andnon-marine metaevaporites.

the unit-cellvolume of ½ (Tl2Pb2As2S6) is calculated as
153.77 A 3, to be compared with the observed one, i.e.
volume of ½ (K2Eu2As2S6) is152.00 A3; the unit-cell
3,
whereas the measured one iscalculated
as151.36A
predicted unit-cell volume of
152.25 A3. Consequently, therichardsollyite (152.00  4 A3) ought to be just a little larger
than that of KEuAsS3. Possibly, the small contraction of themeasured volume of richardsollyite relative to the predicted
one could be due to the lone-electron-pair activity of Tlþ andPb2þ. Among these isotypic compounds, richardsollyite
shows the smallest unit-cell volume, which results from ashorter c parameter and a larger b angle compared to its
isostructural compounds.
Yin et al. (2014) synthesized two seleniosalts with thecompositions KBaAsSe3 and KBaSbSe3. Unit-cell volumes are signiﬁcantly larger than those of the corresponding Eu and Pb counterparts,
owing to the large volume of
Ba2S2 (V = 130.28 A3) and to the Se-to-S substitution. In
addition, Yin et al. (2014) pointed out that, whereas K iseight-fold coordinated in KEuAsS3, it is seven-foldcoordinated in the synthetic phases studied by them.
Indeed, K–Se distances range between 3.27 and 3.79 A in
the As compound; an eighth Se atom is located at 4.14 A.
Consequently, the coordination of K in KBaAsSe3 (as wellas in KBaSbSe3) is similar to that observed inrichardsollyite, where Tl has seven short bonds and an
additional longer bond.
4.3. Thallium and alkaline metals in naturalchalcogenides
The isostructurality between richardsollyite and somesynthetic alkali sulfosalts reminds us about the occurrenceof other isostructural minerals showing Tl–alkali substitution. Potassium chalcogenides are exceptional minerals,
which are limited to the very peculiar geologicalenvironments usually represented by alkaline rocks.
Bukovite, Tl2(Cu,Fe)4Se4, murunskite, K2(Cu,Fe)4S4,
and thalcusite, Tl2Cu3FeS4, belong to the bukovite group,a series of tetragonal sulphides and selenides of Cu and Fe
with Tl and/or K showing a layered structure, with (0 0 1)
layers of edge-sharing (Cu,Fe)-centred tetrahedra alternating with layers of eight-fold coordinated (K,Tl) (e.g.
Makovicky et al., 1980; Pekov et al., 2009). A solid
solution between thalcusite and murunskite is suggestedby the occurrence of Tl-rich murunskite in the Palitra
peralkaline pegmatite, Mount Kedykverpakhk, Lovozero
alkaline massif, Russia (Pekov & Agakhanov, 2008).
Another interesting group of sulphides is represented by
the isostructural picotpaulite, TlFe2S3, rasvumite, KFe2S3,
and pautovite, CsFe2S3; these minerals can also be enrichedin Rb, as reported by Chakhmouradian et al. (2007) for
rasvumite occurring in sodalite syenite from Mont SaintHilaire, Québec, Canada. Their crystal structures have[0 0 1] double chains of edge-sharing Fe-centred tetrahedrainterconnected by ten-fold coordinated Tl atoms which form
zig–zag chains along c (e.g. Balić-Žunić et al., 2008).
The most widespread alkali sulphide is probably
represented by djerﬁsherite, K6Fe25S26Cl. On thecontrary, its Tl-analogue, thalfenisite, Tl6Fe25S26Cl, is

5. Conclusion
Richardsollyite is a new Pb–Tl sulfosalt showing the highest(Pb þ Tl)/As atomic ratio reported to date. In the past two
years ten new mineral species have been described from theLengenbach quarry. They all are structurally related toexisting species: eckerite (Bindi et al., 2015a) to xanthoconite and pyrostilpnite; ralphcannonite and ferrostalderite(Bindi et al., 2015b; Biagioni et al., 2016) to the existing
members of the routhierite isotypic series; argentobaumhauerite (Topa & Makovicky, 2016), argentodufrénoysite
and argentoliveingite (Topa et al., 2016a and c) to their Agfree counterparts, and four new sartorites (Topa et al., 2016b,
2017a, this issue) to the existing members of the sartorite
homologous series. By contrast, the crystal structure of the
new mineral species richardsollyite described in this paper is
new in nature, being previously known only in somesynthetic alkali sulfosalts.
eschweizerbart_xxx

Richardsollyite, a new thallium sulfosalt

This study underlines the importance and the uniqueness of the Lengenbach deposit for the study of Tl
mineralogy. This locality represents a natural laboratory
where subtle geochemical variations in the crystallization
medium gave rise to a remarkable and sometimes
unpredictable variety of mineral species.

687

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Acknowledgements: We greatly appreciate the ﬁeld
support of Ralph Cannon for his careful extraction andexamination of samples from the Lengenbach deposit.
Stefan Ansermet is thanked for his photography. We thank
Edward Grew and Chris Stanley for helping us in
improving the manuscript. The authors are particularly
grateful to an anonymous reviewer for his constructive andvery helpful comments.
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Received 14 November 2016
Modiﬁed version received 9 March 2017
Accepted 3 April 2017eschweizerbart_xxx