Mineralogical Magazine, February 2014, Vol. 78(1), pp. 1–9

Tl-bearing sulfosalt from the Lengenbach quarry, Binn
Valley, Switzerland: Philrothite, TlAs3S5
L. BINDI1,2*, F. NESTOLA3, E. MAKOVICKY4, A. GUASTONI5 AND L. DE BATTISTI6
1

Dipartimento di Scienze della Terra, Università degli Studi di Firenze,Via G. La Pira 4, I-50121 Florence, Italy
CNR  Istituto di Geoscienze e Georisorse, Sezione di Firenze, Via G. La Pira 4, I-50121 Florence, Italy
3
Dipartimento di Geoscienze, Università di Padova, Via Gradenigo 6, I-35131, Padua, Italy
4
Department of Geoscience and Resource Management, University of Copenhagen, Østervoldgade 10, 1350
Copenhagen, Denmark
5
Museo di Mineralogia, Università di Padova, Via Giotto 1, I-35122, Padua, Italy
6
FGL (Forschungsgemeinschaft Lengenbach), Via dello Storno 18, I-20147 Milan, Italy
2[Received 7 October 2013; Accepted 19 November 2013; Associate Editor: P. Leverett]
ABSTRACT

Philrothite, ideally TlAs3S5, is a new mineral from the Lengenbach quarry in the Binn Valley, Valais,
Switzerland. It occurs as very rare crystals up to 200 mm across on realgar associated with smithite,rutile and sartorite. Philrothite is opaque with a metallic lustre and shows a dark brown streak. It isbrittle; the Vickers hardness (VHN25) is 128 kg/mm2 (range: 120137) (Mohs hardness of 33). In
reﬂected light philrothite is moderately bireﬂectant and weakly pleochroic from dark grey to light grey.
Under crossed polars it is anisotropic with grey to bluish rotation tints. Internal reﬂections are absent.
Reﬂectance percentages for the four COM wavelengths (Rmin and Rmax) are: 26.5, 28.8 (471.1 nm),
25.4, 27.2 (548.3 nm), 24.6, 26.3 (586.6 nm) and 24.0, 25.1 (652.3 nm), respectively.
Philrothite is monoclinic, space group P21/c, with a = 8.013(2), b = 24.829(4), c = 11.762(3) Å, b =132.84(2)º, V = 1715.9(7) Å3, Z = 8. It represents the N = 4 homologue of the sartorite homologous
series. In the crystal structure [R1 = 0.098 for 1217 reﬂections with I > 2s(I)], Tl assumes tricapped
prismatic sites alternating to form columns perpendicular to the b axis. Between the zigzag walls of Tl
coordination prisms, coordination pyramids of As(Sb) form diagonally-oriented double layers
separated by broader interspaces which house the lone electron pairs of these elements.
The eight strongest calculated powder-diffraction lines [d in Å (I/I0) (hkl)] are: 12.4145 (52) (020);
3.6768 (100) (1̄61); 3.4535 (45) (131); 3.0150 (46) (1̄53); 2.8941 (52) (1̄81); 2.7685 (76) (230); 2.7642(77) (2̄34); 2.3239 (52) (092). A mean of ﬁve electron microprobe analyses gave Tl 26.28(12), Pb
6.69(8), Ag 2.50(4), Cu 0.04(2), Hg 0.07(2), As 32.50(13), Sb 3.15(3), S 26.35(10), total 97.58 wt.%,
corresponding, on the basis of a total of nine atoms, to (Tl 0 . 7 8 9 Pb 0 . 1 9 8 ) S = 0 . 9 8 7(As2.662Sb0.159Ag0.142Cu0.004Hg0.002)S=2.969S5.044. The new mineral has been approved by theCommission on New Minerals, Nomenclature and Classiﬁcation (CNMNC) of the International
Mineralogical Association (2013-066) and named for Philippe Roth (b. 1963), geophysicist and wellknown mineral expert on the Lengenbach minerals for more than 25 years.
K EY WORDS : philrothite, new mineral, Tl-sulfosalt, Lengenbach, Switzerland.

Introduction
THE Lengenbach quarry located in the Binn
Valley, Canton Valais, Switzerland is one of the* E-mail: luca.bindi@unifi.it
DOI: 10.1180/minmag.2014.078.1.01# 2014 The Mineralogical Society

premium localities for Tl-bearing sulfosalts. Morethan 15 Tl-bearing minerals are reported from thisquarry and for 12 of them Lengenbach is the typel o c a l i t y , w i t h d a l n e g r o i t e T l 5 x P b 2 x(As,Sb)21xS34 (x ~ 1) (Nestola et al., 2010;
Bindi et al., 2010) and raberite Tl5Ag4As6SbS15

L. BINDI ET AL.

(Bindi et al., 2012) being the more recently
described species.
The specimen containing philrothite comesfrom the realgar-rich zone (the so-called zone 1;
Graeser et al., 2008) and was sampled in 1988.
Minerals associated with philrothite are realgar,
smithite, rutile and sartorite. This mineral, as wellas the other Tl minerals at Lengenbach,presumably represent products of late-stage Tland As-bearing hydrothermal solutions during
Alpine metamorphism (Hofmann and Knill,
1996).
Philrothite was approved as a new mineral by
the CNMNC (2013-066). The mineral namehonours Dr Philippe Roth (b. 1963), a wellknown mineral expert on the Lengenbach minerals
for more than 25 years. He is currently Presidentof the FGL (Forschungsgemeinschaft Lengenbach;
literally: research community Lengenbach) andhas analysed several specimens from this deposit
and published many articles about Lengenbachminerals including a book on the minerals ﬁrst
discovered in Switzerland and minerals named
after Swiss individuals (Roth, 2007). The namereﬂects part of the ﬁrst name (Phil for Philippe)
and the last name (Roth). The holotype material isdeposited in the mineralogical collection of theMuseum of Mineralogy of the Department ofGeosciences at the University of Padova (Italy),
under catalogue number MMP M12605.
In this study we report the description of the
new mineral philrothite together with thedetermination of its crystal structure.

FIG. 1. SEM-BSE image of irregular grains of philrothite(brighter phase) on realgar.

from dark grey to a light grey. Between crossed
polars, philrothite is anisotropic with grey tobluish rotation tints. Internal reﬂections are absent
and there is no optical evidence of growthzonation.
Reﬂectance measurements were performed in
air by means of a MPM-200 Zeiss microphotometer equipped with a MSP-20 system processor
on a Zeiss Axioplan ore microscope. The ﬁlament
temperature was ~3350 K. An interference ﬁlter
was adjusted, in turn, to select four wavelengths
for measurement (471.1, 548.3, 586.6 and652.3 nm). Readings were taken for specimen
and standard (SiC) maintained under the same
focus conditions. The diameter of the circularmeasuring area was 0.1 mm. Reﬂectance percentages for the four COM wavelengths (Rmin andRmax) are 26.5, 28.8 (471.1 nm), 25.4, 27.2
(548.3 nm), 24.6, 26.3 (586.6 nm), and 24.0,
25.1 (652.3 nm), respectively.

Physical and optical properties
Philrothite occurs as very rare crystals on realgar(Fig. 1). The mineral exhibits an anhedral grainmorphology, and shows no inclusions of, orintergrowths with, other minerals. The maximum
grain size of philrothite is ~200 mm. It is black incolour and shows a dark brown streak. The
mineral is opaque in transmitted light and exhibitsa metallic lustre. No cleavage is observed and thefracture is uneven. The calculated density (Z = 8)
for the empirical formula is 4.635 g/cm3.
Unfortunately, the density could not be measured
because of the small grain size. Micro-indentation
measurements carried out with a VHN load of 25
g gave a mean value of 128 kg/mm2 (range:120137) corresponding to a Mohs hardness of33.
In plane-polarized incident light philrothite ismoderately bireﬂectant and weakly pleochroic

X-ray crystallography and crystal-structure
determination
A small crystal fragment (55 mm660 mm6
65 mm) was selected for the single-crystal X-ray
diffraction study that was carried out using a
STOE-STADI IV CCD single-crystal diffractometer (Table 1). The analysis of the systematicabsences led unequivocally to the choice of thespace group P21/c. The positions of most of theatoms (Tl and As/Sb atoms) were determined bymeans of direct methods of the SHELXS program(Sheldrick, 2008). A least-squares reﬁnement on
F2 using these heavy-atom positions and isotropic
temperature factors produced an R factor of2

PHILROTHITE A NEW TL-BEARING SULFOSALT FROM LENGENBACHTABLE 1. Crystallographic data and reﬁnement parameters for philrothite.
Crystal data
Ideal formula
Crystal system
Space group
Unit-cell parameters (Å, º)
Unit-cell volume (Å3)
Z
Crystal size (mm)TlAs3S5
monoclinic
P21/c
8.013(2) 24.829(4) 11.762(3) 132.84(2)1715.9(7)80.05560.06060.065

Data collection
Diffractometer
Temperature (K)Radiation, wavelength (Å)
2y max for data collection (º)
Crystal–detector dist. (mm)h, k, l ranges
Axis, frames, width (º), time per frame (s)Total reflections collected
Unique reflections (Rint)
Unique reflections I > 2s(I)Data completeness to ymax (%)
Absorption correction method

STOE-STADI IV CCD
298(3)
MoKa, 0.71073
59.66
60–11  10, –34  32, –16  15o, 645, 1.00, 50
18958
4788 (0.156)
1217
99.4
X-RED and X-SHAPE

Structure refinement
Refinement method
Data/restraints/parameters
R1 [I > 2s(I)], wR2 [I > 2s(I)]R1 all, wR2 allGoodness-of-fit on F2
Largest diff. peak and hole (e–/Å3)

Full-matrix least-squares on F2
1217/0/85
0.0985, 0.1324
0.1158, 0.1501
1.215
3.92, –3.52

Rint = (n/n  1)1/2[F2o  Fo (mean)2]/SF2o
R1 = S||Fo|  |Fc||/S|Fo|; wR2 = {S[w(F2o  F2c )2]/S[w(F2o)2]}1/2;* w = 1/[s2(F2o) + (aP)2 + bP], where P = (max(F2o,0) + 2F2c )/3;
GooF = {S[w(F2o  F2c )2]/(n  p)}1/2; where n is the number of reﬂections and p is the number of reﬁned parameters.

coordinates and isotropic displacement parameters are reported in Table 2 (anisotropic
ADPs for the two Tl positions can be found in
the accompanying CIF). Bond distances are given
in Table 3.
The authors attempted to collect a powder
pattern with an automated CCD-equipped
Oxford Diffraction Xcalibur PX diffractometerusing CuKa radiation but the small size of thecrystal, coupled with its poor diffraction quality(see above), failed to yield publication-quality
results. The calculated X-ray powder-diffraction
pattern, computed with the atom coordinates andoccupancies reported in Table 2, is given in
Table 4. Structure factors (Table 5) have been
deposited with the Principal Editor of
Mineralogical Magazine and are available at

0.286. Three-dimensional difference Fourier
synthesis yielded the position of the remaining
sulfur atoms. The program SHELXL (Sheldrick,2008) was used for the reﬁnement of the structure.
The occupancy of all the sites was left free to vary
(Tl vs. vacancy; As vs. Sb; S vs. vacancy) andthen ﬁxed to the resulting value (Table 2). Neutral
scattering curves for Tl, As, Sb and S were takenfrom the International Tables for X-ray
Crystallography (Ibers and Hamilton, 1974). At
the last stage, with anisotropic atomic displacement parameters for the two Tl atoms and no
constraints, the residual value settled at R1 =0.0985 for 1217 observed reﬂections [2s(I) level]and 85 parameters and at R1 = 0.1158 for all 4788
independent reﬂections. Experimental details and
R indices are given in Table 1. Fractional atomic
3

L. BINDI ET AL.

TABLE 2. Atoms, site occupancy (s.o.f.), fractional atom coordinates (Å), and isotropic atomic displacement
parameters (Å2) for philrothite.
Atoms.o.f.

x/a

y/b

z/c

Uiso

Tl1
Tl2
As1
As2
As3
As4
As5
As6
S1
S2
S3
S4
S5
S6
S7
S8
S9
S10

Tl1.00
Tl1.00As1.00As1.00As1.00As0.56(2)Sb0.44
As1.00As1.00
S1.00
S1.00
S1.00
S1.00
S1.00
S1.00
S1.00
S1.00
S1.00
S1.00

0.636(1)0.156(1)–0.020(3)0.506(4)0.893(4)0.421(3)0.330(4)0.788(3)0.610(8)0.011(8)0.528(8)0.985(9)0.093(8)0.622(6)0.770(6)0.638(7)0.844(7)0.459(9)0.7863(3)0.7928(3)0.8485(8)0.6442(9)0.5788(9)0.9367(8)0.540(1)0.5517(8)0.838(2)0.667(2)0.613(2)0.616(3)0.778(3)0.726(1)0.979(1)0.480(2)0.587(2)0.584(2)0.8763(9)0.3728(8)0.610(2)0.642(2)0.359(3)0.387(2)0.162(3)0.605(2)0.421(6)0.330(6)0.170(6)0.603(7)0.600(7)0.636(4)0.585(4)0.320(5)0.828(5)0.433(6)0.040(3)0.032(2)0.036(6)0.052(7)0.069(8)0.065(9)0.085(9)0.039(5)0.046(8)0.052(8)0.046(9)0.079(8)0.090(8)0.045(8)0.034(9)0.028(9)0.040(8)0.059(8)History of Milan. The chemical composition wasthen determined using wavelength dispersive
analysis (WDS) by means of a CAMECACAMEBAX electron microprobe. Major andminor elements were determined at 20 kV
accelerating voltage and 20 nA beam current,
1 mm beam size, and with 15 s as the counting
time. For the WDS analyses the following lines

http://www.minersoc.org/pages/e_journals/
dep_mat_mm.html).
Chemical composition
A preliminary chemical analysis using energy
dispersive spectrometry was performed using a
SEM JEOL-5610 LV at the Museum of Natural

TABLE 3. Selected bond distances (Å) for philrothite.
Tl1– S1
S2
S3
S4
S5
S5
S6
S6

3.14(2)
3.53(3)3.13(3)3.28(3)3.23(2)
3.13(2)3.15(3)3.13(3)Tl2– S1
S2
S3
S4
S5
S5
S6
S6

3.50(3)3.25(4)3.59(3)3.34(2)3.08(4)3.38(4)3.26(3)3.15(2)

As1–S1S2
S5

2.26(1)2.46(1)1.95(1)As2–S1S6
S9S10

2.68(1)2.27(1)2.52(1)2.72(1)As3–S2S3
S4

2.50(2)2.27(1)2.64(1)As4–S1S7
S7S8

2.79(2)2.37(1)2.77(1)2.37(1)As5–S3S8
S10

2.40(2)2.32(1)2.78(2)

As6–S4S9
S10

2.21(2)2.50(2)2.16(1)

4

PHILROTHITE A NEW TL-BEARING SULFOSALT FROM LENGENBACHTABLE 4. Calculated X-ray powder diffraction pattern for philrothite.
I

dcalc (Å)

h

k

l

I

dcalc (Å)

h

k

l

52
6
18
5
5
13
39
21
12
27
43
100
21
25
13
45
38
21
12
29
12
43
46
25
24
52
17
8
10
76
77
5
6
6
20
23
6
12
8
6
5
9

12.41457.62576.73245.87565.75694.9071
4.24874.00653.95533.82433.81293.67683.63373.62883.60623.45353.4492
3.36623.25603.11813.10363.01793.01502.91742.91232.89412.87842.79902.79672.76852.76422.74322.68852.65582.65542.65152.64252.61122.59302.59122.54192.4535

0
1̄
1̄
1
1̄
1̄
0
2̄
2̄
0
2̄
1̄
1
1̄
2̄
1
1̄
2̄
0
2̄
0
1
1̄
2
2̄
1̄
2̄
1
1̄
2
2̄
1̄
1̄
2̄
2
2̄
1̄
3̄
1
1̄
3̄
3̄

2
1
2
0
3
4
1
0
1
3
2
6
2
2
3
3
3
4
5
5
8
5
5
1
1
8
6
6
6
3
3
8
1
7
4
4
2
2
7
7
3
4

0
1
1
0
1
1
2
2
2
2
2
1
1
3
2
1
3
2
2
2
0
1
3
0
4
1
2
1
3
0
4
2
4
2
0
4
4
3
1
3
3
3

11
7
52
17
19
16
45
5
5
6
6
13
15
15
7
5
8
14
14
14
7
7
6
5
13
12
5
10
11
7
5
7
8
8
6
9
5
6
6
6
5

2.37172.35232.32392.24412.23252.23142.15612.06912.06642.06372.02451.91901.91351.91131.9064
1.8782
1.87551.86061.8593
1.8384
1.81801.8172
1.81661.81551.81321.81071.8031
1.78991.78871.77351.75401.73161.7296
1.72851.55601.5517
1.39951.36971.36331.36301.3184

1̄
3̄
0
3̄
1
1̄
0
0
3̄
3̄
3̄
3̄
3̄
3̄
4̄
2
2̄
1
1̄
2̄
4̄
1
1̄
4̄
4̄
4̄
4̄
2
2̄
0
3̄
1̄
1
1̄
3
5̄
2
0
1
1̄
6̄

10
5
9
6
9
9
0
12
5
5
8
9
7
7
4
2
2
6
6
12
0
12
12
0
1
1
6
11
11
14
9
14
8
8
6
4
12
14
17
17
3

1
3
2
3
1
3
4
0
1
5
3
3
1
5
4
2
6
3
5
2
2
1
3
6
2
6
4
0
4
0
1
1
3
5
1
5
2
4
1
3
6

The powder pattern was calculated and indexed on the basis of a = 8.013(2), b = 24.829(4),c = 11.762(3) Å, b = 132.84(2)º, and with the atomic coordinates and occupancies reported inTable 2. The strongest intensities are given in bold.

and pyrite (S). The crystal fragment was found tobe homogeneous within analytical error. The
average chemical compositions (ﬁve analyses on
different spots) together with wt.% ranges of
elements are reported in Table 6. On the basis ofwere used: TlMa, PbMa, AgLa, CuKa, HgLa,
AsLa, SbLa and SKa. The standards employed
were: synthetic Tl2Se (Tl), galena (Pb), Ag-pureelement (Ag), Cu-pure element (Cu), cinnabar(Hg), synthetic As2S3 (As), synthetic Sb2S3 (Sb)5

L. BINDI ET AL.

TABLE 6. Electron microprobe analyses (means, ranges and standard deviations) and atomic
ratios (on the basis of nine atoms) for philrothite.

Tl
Pb
Ag
Cu
Hg
As
Sb
S
Total

Wt.%

Range

s

Atom

Atomic ratios

26.28
6.69
2.50
0.04
0.07
32.50
3.15
26.35
97.58

24.3326.98
6.256.92
2.302.53
0.020.09
0.000.12
31.9733.09
3.103.37
26.1226.91
96.6097.90

0.12
0.08
0.04
0.02
0.02
0.13
0.03
0.10

Tl
Pb
Ag
Cu
Hg
As
Sb
S
Satoms

0.789
0.198
0.142
0.004
0.002
2.662
0.159
5.044
9.000

the b axis, organized into zigzag layers parallel to(010). Both Tl1 and Tl2 show irregular coordinations with mean bond distances of 3.22 and3.32 Å. Such values are in agreement with thesum of the ionic radii of Tl+ and S2 (3.34 Å;
Shannon, 1976) and suggest that the bonding of Tl
should be ionic in this structure although theeccentric position of Tl2 suggests a degree of loneelectron pair activity. The TlS distances inphilrothite are also in keeping with those observed
for the Tl positions (Tl1 and Tl3) in the structureof gabrielite, Tl2AsCu2As3S7 (3.383.49 Å;Balić-Žunić et al., 2006), the Tl positions

nine atoms, the empirical formula of philrothite is(Tl 0 .7 89 Pb 0.19 8 ) S=0.987 (As 2.6 62 Sb 0.159 Ag 0.142
Cu0.004Hg0.002)S=2.969S5.044. The simpliﬁed ideal
formula is TlAs3S5, which requires Tl 34.67, As
38.13, S 27.20, total 100.00 wt.%.
Results and discussion
Philrothite can be considered the N = 4
homologue of the sartorite homologous series(Makovicky, 1985, Moëlo et al., 2008). In the
structure (Fig. 2), Tl assumes tricapped prismatic
sites alternating to form columns perpendicular to

FIG. 2. The crystal structure of philrothite projected upon (001). Grey spheres are Tl, small black ones As, and large
white ones are S. Zigzag (010) walls of Tl-polyhedra and two types of lone electron pair micelles (large and small)are evident. The horizontal direction corresponds to the b axis. Further details are given in the text.

6

PHILROTHITE A NEW TL-BEARING SULFOSALT FROM LENGENBACH

longer than in other As polyhedra and, presumably, might concentrate some of the other minor
cations (Ag). The walls are interconnected withthe opposite wall of the double layer by short
AsS bonds (these are the vertices of AsS5
pyramids). The only As site which interconnectswith the wall of the next double layer, byinfrequent short AsS bonds, is As3. In thisway, large lone electron pair micelles are formedby As1 and As2, as well as As5 and As6, with thebridging long AsS distances of the order of
3.43.5 Å, and small lone electron pair micelles,
formed by As3 and As4, with AsS distances ofthe order of 2.8 Å. Interconnection of surface
crankshafts and groups, as short bonds across the
double layer, occurs between S9Tl2, As6S4,As5S3, and As1S5, As2S6.
Adjacent As-based slabs are related by the 21
and c glide operations of the space group. The
quality of diffraction data, revealing how poorly
crystallized the only known crystals are, allowed
recognition and description of principles of thestructure but the details of occupancy andespecially the interatomic distances are insufﬁciently constrained (Table 3).
The philrothite structure is related to that ofpierrotite (Engel et al., 1983), which is the N = 3
homologue of sartorite (Berlepsch et al., 2003). In(Tl1Tl5) in the structure of raberite,
Tl5Ag4As6SbS15 (3.333.41 Å; Bindi et al.,2012), and that found for the Tl position insicherite, TlAg2(As,Sb)3S6 (3.34 Å; Graeser et al.,2001).
Between the zigzag walls of Tl coordination
prisms, coordination pyramids of As(Sb) form
diagonally oriented double layers [approximately(13̄1)] separated by broader interspaces whichhouse the lone electron pairs of these elements(Fig. 3). Arsenic atoms in a wall of the double
layer have pairs of short AsS bonds oriented
either sideways (As1 and As3 outwards in respect
to the layer thickness, As2 and As4 inwards, with
As6 in the centre of the layer) or upwards (As5).
They are interconnected via these short AsS
bonds into crankshaft chains S9–M6–S10–M5–
S8–M4–S7, running diagonally across the ~(13̄1)
surfaces of double layers. They all have strongly
trapezoidal bases of coordination pyramids. The
As2 and As4 sites have a more complex schemeof bonds in the base of the pyramid (Table 3). The
reﬁnement of the site occupancies concentrated
the Sb content into the mixed As4 site (Table 2).
In addition to the crankshaft scheme, the wall
also contains separate AsS3 polyhedra (As1 andAs3). The remaining As2 site has a different
coordination showing four similar distances

FIG. 3. Distribution of short AsS bonds in a (13̄1) double layer from the As-rich (010) slabs in the structure ofphilrothite. A crankshaft chain (diagonal, centre) and individual As1, As2 and As3 groups are illustrated, with theirinterconnections across the double layer. For colouring see Fig. 2.

7

L. BINDI ET AL.

Acknowledgements

this structure, however, stoichiometry requires
alternation of Tl and Sb in each prismatic column,
which is not observed in philrothite. The
philrothite structure shares the principal features,
which are typical of sartorite homologues, withsartorite and rathite (Berlepsch et al., 2002, 2003).
According to the calculation rules ofMakovicky (1985), the chemical composition ofphilrothite gives the homologue order N value of
3.76, in fair agreement with the crystallographic
value of N = 4; the difference expresses analyticalerrors. It is only ~20% away from the ideal
formula TlAs3S5 which is the maximum possible
substitution by Tl and (As,Sb). The traces of 2Pb$ Ag + (Sb,As) substitution do not reach even
25% of the possible substitution range.
The Tl + (Sb,As) substitution in the sartorite
homologous series is known for the compositions
close to the Pb(As,Sb) and Tl(As,Sb)
endmembers; data for the central portions of therange are absent. Thallium can substitute only inthe capped prismatic sites, usually substituting forlead. The charge compensating M3+, connectedwith this substitution, can either replace Pb in theintermediate slabs or it can replace half of the Pb
in the prismatic sites. The latter substitution takes
place in the substituted N = 3 homologues because
they do not contain Pb in the intermediate slabs.
Approaching the highest substitution percentage,
seen in philrothite (N = 4), the potential M2+ sites
in the slabs are progressively replaced by M3+,
which, according to our a priori reasoning, canmove there from the prismatic sites and enable Tl
to ﬁll the prismatic sites completely.
To our knowledge, philrothite has neither
synthetic analogues nor natural ones. However,
although with a different structure, it is noteworthy that the chemical Sb-analogue of philrothite, the synthetic sulfosalt TlSb3S5 (Gostojic
et al., 1982), has the crystal structure which is an
N = 3 homologue of lillianite (Makovicky and
Balić-Žunić, 1993). It exhibits a monoclinic
symmetry with unit-cell dimensions a =7.225(2), b = 15.547(3), c = 8.946(3) Å, b =113.55(3)º and space group P21/c. The structure
consists of Sb-pyramids forming inﬁnite [Sb3S5]
slabs parallel to (010). They are glide-reﬂection
twinned on (010) TlS layers of bicapped
coordination prisms. The former slabs approximate a slightly distorted PbS archetype andcontain large lone electron pair micelles, arranged
diagonally and en echelon.

The research was supported by ‘‘progetto
d’Ateneo 2006, University of Padova’’ to FN
and by ‘‘progetto d’Ateneo 2012, University ofFirenze’’ to LB.
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