Mineralogical Magazine, October 2015, Vol. 79(5), pp. 1089–1098

Ralphcannonite, AgZn2TlAs2S6, a new mineral of therouthierite isotypic series from Lengenbach, Binn Valley,
Switzerland
LUCA BINDI1,*, CRISTIAN BIAGIONI2, THOMAS RABER3, PHILIPPE ROTH4 AND FABRIZIO NESTOLA5
1

Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Via G. La Pira, 4, I-50121 Firenze, Italy
Dipartimento di Scienze della Terra, Università di Pisa, Via Santa Maria, 53, I-56126 Pisa, Italy
3
FGL (Forschungsgemeinschaft Lengenbach), Edith-Stein-Str. 9, D-79110 Freiburg, Germany
4
FGL (Forschungsgemeinschaft Lengenbach), Ilanzhofweg 2, CH-8057 Zurich, Switzerland
5
Dipartimento di Geoscienze, Università di Padova, Via Gradenigo, 6, I-35131 Padova, Italy
2[Received 7 December 2014; Accepted 22 January 2015; Associate Editor: J. Majzlan]
ABSTR ACTThe new mineral species ralphcannonite, AgZn2TlAs2S6, was discovered in the Lengenbach quarry, Binn
Valley, Wallis, Switzerland. It occurs as metallic black equant, isometric to prismatic crystals, up to 50 µm,
associated with dufrénoysite, hatchite, realgar and baryte. Minimum and maximum reflectance data for
COM wavelengths in air are [λ (nm): R (%)]: 471.1: 25.8/27.1; 548.3: 25.2/26.6; 586.6: 24.6/25.8; 652.3:
23.9/24.8. Electron microprobe analyses give (wt.%): Cu 2.01(6), Ag 8.50(16), Zn 10.94(20), Fe 3.25(8),Hg 7.92(12), Tl 24.58(26), As 18.36(19), Sb 0.17(4), S 24.03(21), total 99.76(71). On the basis of 12 atoms
per formula unit, the chemical formula of ralphcannonite is Ag0.63(2)Cu0.25(2)Zn1.35(5)Fe0.47(1)Hg0.32(2)Tl0.97(3)[As1.97(6)Sb0.01(1)]Σ1.98(5)S6.03(8). The new mineral is tetragonal, space group I 42m, with a = 9.861(2), c = 11.125(3) Å, V = 1081.8(4) Å3, Z = 4. The main diffraction lines of the calculated powder diagram
are [d(in Å), intensity, hkl]: 4.100, 85, 211; 3.471, 40, 103; 2.954, 100, 222; 2.465, 24, 400; 2.460, 39, 303.
The crystal structure of ralphcannonite has been refined by X-ray single-crystal data to a final R1 = 0.030, on
the basis of 140 observed reflections [Fo > 4σ(Fo)]. It shows a three dimensional framework of (Ag,Zn)centred tetrahedra (1 M1 + 2 M2), with channels parallel to [001] hosting TlS6 and (As,Sb)S3 disymmetricpolyhedra. Ralphcannonite is derived from its isotype routhierite M1CuM2Hg2TlAs2S6 through the double
heterovalent substitution M1Cu+ + M2Hg2+ → M1Zn2+ + M2Ag+. This substitution obeys a steric constraint,with Ag+, the largest cation relative to Zn2+ and Cu+, entering the largest M2 site, as observed in arsiccioite.
The ideal crystal-chemical formula of ralphcannonite is M1ZnM2(Zn0.5Ag0.5)2TlAs2S6.
K E Y WO R D S : ralphcannonite, new mineral species, sulfosalt, thallium, zinc, silver, arsenic, crystal structure,

Lengenbach, Binn Valley, Switzerland.

Introduction
AMONG the world-class localities for the study ofsulfosalt assemblages, Lengenbach occupies an
outstanding position, owing to the large number ofsulfosalt species (more than 30 species as of* E-mail: luca.bindi@unifi.it
DOI: 10.1180/minmag.2015.079.5.05© 2015 The Mineralogical Society

November 2014) with it as their type locality andto the complex and intriguing geochemistry, withan original combination of numerous cations (Pb,Tl, Ag, Cu, Zn, Cd, Sn, As and Sb). In particular,
Lengenbach can be considered the most important
locality world-wide for the study of the crystalchemistry of thallium sulfosalts. Indeed, 19 thallium
sulfosalts have been identified from the Lengenbach
dolostone so far; among these, 15 were firstdescribed from this locality (Table 1).

LUCA BINDI ET AL.

Following the sulfosalt systematics given byMoëlo et al. (2008), thallium sulfosalts from
Lengenbach can be classified in the following
groups (the very recently approved mineral spaltiite
is not considered because its crystallographic data
have not been published yet):(1) sulfosalts with an atom ratio of cation/chalcogen = 1: the hatchite isotypes (hatchite, wallisite) and the two members of the weissbergite
homeotypic pair, i.e. weissbergite andlorándite;(2) lead sulfosalts based on large 2D fragments of
the PbS/SnS archetype, represented bymembers of the sartorite homologous series( philrothite) and related compounds (dalnegroite, parapierrotite);(3) specific Tl sulfosalts (structures with SnS
layers), particularly represented by membersof the hutchinsonite merotypic series (bernardite, hutchinsonite, edenharterite, jentschite,
imhofite). Other minerals belonging to thistype are sicherite, gabrielite and ernigglite.
Possibly, the recently described mineral raberite could be classified within this group;(4) sulfosalts with an excess of small monovalentcations (Ag,Cu) relative to (As, Sb, Bi),
represented by the member of the routhierite
isotypic series stalderite.

This latter mineral, as well as the members of therouthierite isotypic series, deserve a careful study,
owing to their variable crystal chemistry, possiblyreflecting the geochemistry of the crystallizing
medium, as described for the routhierite-arsiccioite
pair by Biagioni et al. (2014b). Preliminary energy
dispersive spectrometry (EDS) chemical analyses
performed on specimens of stalderite showed theoccurrence of Ag- and Fe-rich varieties. In particular, a specimen examined in 2003 proved to be an
Ag-rich Fe-bearing stalderite. In 2013, new EDS
chemical analyses confirmed its high Ag content,suggesting the need for a more accuratecharacterization.
Crystallographic studies and chemical analyses
allowed us to describe this phase as the new mineralralphcannonite. The mineral and its name havebeen approved by the Commission on New
Minerals, Nomenclature and Classification of theInternational Mineralogical Association (IMA
2014-077, Bindi et al., 2015). The holotype
specimen of ralphcannonite is deposited in themineralogical collection of the Museo di Storia
Naturale, Università degli Studi di Firenze, Via La
Pira 4, Florence, Italy, under catalog number 3145/I.
The name honours Ralph Cannon (b. 1956) for
his contribution to the knowledge of the mineralogy of the Lengenbach quarry. Ralph Cannon

TABLE 1. Thallium sulfosalts from Lengenbach. Sulfosalts that have their type locality at Lengenbach are in bold.
MineralBernardite
Dalnegroite
Edenharterite
Ernigglite
Gabrielite
Hatchite
Hutchinsonite
Imhofite
Jentschite
Lorándite
Parapierrotite
Philrothite
Raberite
Ralphcannonite
Sicherite
Spaltiite
Stalderite
Wallisite
Weissbergite

Chemical formula

References

TlAs5S8(Tl2PbSb)(Sb3As6)S17
TlPbAs3S6
SnTl2As2S6
Cu2AgTl2As3S7
AgTlPbAs2S5
TlPbAs5S9
Tl5.8As15.4S26
TlPbAs2SbS6
TlAsS2
TlSb5S8
TlAs3S5
Ag4Tl5As6SbS15
AgZn2TlAs2S6
Ag2Tl(As,Sb)3S6
Cu2Tl2As2S5
CuZn2TlAs2S6
CuTlPbAs2S5
TlSbS2

Hofmann et al. (1993)
Nestola et al. (2009)
Graeser and Schwander (1992)
Graeser et al. (1992)
Graeser et al. (2007)
Solly and Smith (1912)
Solly (1905)
Burri et al. (1965)
Graeser and Edenharter (1997)
Graeser (1967)
Nestola (unp. data, 2014)
Bindi et al. (2014)
Bindi et al. (2012)
This work
Graeser et al. (2001)
Graeser et al. (2014)
Graeser et al. (1995)
Nowacki (1965)
Roth et al. (2014)

1090

RALPHCANNONITE, AgZn2TlAs2S6, A NEW MINERAL OF THE ROUTHIERITE ISOTYPIC SERIES

started working in the Lengenbach quarry in 1996.
In 2003, when the Lengenbach Research
Association(FGL,
Forschungsgemeinschaft
Lengenbach) was founded, he was appointed as
Technical Head for specimen extraction, an activity
he has been carrying out ever since with great
dedication and intuition. He has also analysed
several specimens from this locality and has
published many papers about Lengenbachmineralogy.
The aim of this paper is the description of the
new mineral species ralphcannonite and its relationships with the other members of the routhierite
isotypic series.
FIG. 1. Ralphcannonite, equant crystals on realgar.

Occurrence and mineral description
The Lengenbach quarry (latitude 46°21′54″N, longitude 8°13′15″E) exploits a Triassic dolostone
overlying the gneiss basement at the northern frontof the Monte Leone Nappe, in the Penninic Domainof the Alps. These rocks have been metamorphosed
up to upper greenschist–lower amphibolite facies
conditions. The dolostone is 240 m thick at
Lengenbach; mineralization occurs in the uppermost
part of the sequence, close to the contact withthe overlying Jurassic to Lower Cretaceous
Bündnerschiefer. Hofmann and Knill (1996) recognized four major types of mineralization: (1)stratiform layers of pyrite with minor galena,
sphalerite and xenomorphic sulfosalts; (2) massive
to interstitial sulfosalt accumulations; (3) discordantsulfosalt and sulfide veins; and (4) idiomorphic
crystals within druses and open fissures.
Ralphcannonite was discovered in the type (2)mineralization, corresponding to the so-called‘Zone 1’ of Graeser et al. (2008). The specimen
studied was originally found in 1989 by theArbeitsgemeinschaft Lengenbach (Lengenbach
Working Association). Then, via the Natural History
Museum in Bern, the specimen found its way into
the private collection of one of the authors (TR).

lustre is metallic. Micro-indentation measurements
carried out with a VHN load of 30 g give a meanvalue of 120 kg mm−2 (range: 116–128; 3 measurements) corresponding to a Mohs hardness of∼2–2½.
In plane-polarized incident light, ralphcannonite
is greyish in colour. Under crossed polars, it is very
weakly anisotropic, with greyish to light blue
rotation tints. Internal reflections are very weak.
There is no optical evidence of growth zonation.
Reflectance measurements were performed in air
by means of a MPM-200 Zeiss microphotometerequipped with a MSP-20 system processor on a Zeiss
Axioplan ore microscope. The filament temperaturewas ∼3350 K. An interference filter was adjusted, inturn, to select four wavelengths (approximating thoserecommended by the Commission on Ore
Mineralogy of the IMA) for measurement (471.1,
548.3, 586.6 and 652.3 nm). Readings were taken for
specimen and standard (SiC) maintained under thesame focus conditions. The diameter of the circularmeasuring area was 0.1 mm. Reflectance percentages for Rmin and Rmax are 25.8, 27.1 (471.1 nm),25.2, 26.6 (548.3 nm), 24.6, 25.8 (586.6 nm) and
23.9, 24.8 (652.3 nm), respectively.
Owing to the small amount of pure material
available, the density was not measured; thecalculated density, based on the empirical formula(see below), is 4.927 g·cm−3.
In the specimen studied, ralphcannonite is associated with hatchite, dufrénoysite, realgar and baryte.

Physical and optical properties
Ralphcannonite was observed as euhedral crystals;
on the basis of scanning electron microscopy images(Fig. 1) and the crystal forms reported by Graeser
et al. (1995) for stalderite, the dominant forms could
be the prism {110} and the basal pynacoid {001},
with the bipyramids {101} and {111}, as well as theprism {100} as accessory forms. Ralphcannonite isbrittle, with irregular fracture; the streak is black, theChemical analysis

1091

A preliminary chemical analysis using EDS
performed on the crystal fragment used for theLUCA BINDI ET AL.

TABLE 2. Microprobe analyses of ralphcannonite:chemical composition as wt.% and number ofatoms on the basis of 12 atoms per formula unit
(a.p.f.u.).
Element

wt.%

range

e.s.d.

Cu
Ag
Zn
Fe
Hg
Tl
As
Sb
S
Total

2.01
8.50
10.94
3.25
7.92
24.58
18.36
0.17
24.03
99.76

1.78–2.22
8.19–8.80
10.25–11.33
3.10–3.34
7.10–8.50
23.87–25.26
17.58–18.96
0.09–0.25
23.61–24.66
99.25–100.88

0.06
0.16
0.20
0.08
0.12
0.26
0.19
0.04
0.21
0.71

Cu
Ag
Zn
Fe
Hg
Tl
As
Sb
S
Ev

a.p.f.u.
0.255
0.634
1.346
0.468
0.318
0.968
1.972
0.011
6.030
0.1

range
0.226–0.279
0.606–0.663
1.262–1.400
0.449–0.482
0.286–0.344
0.940–1.005
1.908–2.037
0.006–0.016
5.949–6.141–3.7–3.0

e.s.d.
0.022
0.021
0.054
0.013
0.022
0.028
0.057
0.004
0.078
2.5

Crystallography

Valence equilibrium: Ev (%) = [Σ(val+) – Σ(val–)]× 100/Σ(val–).

single-crystal X-ray diffraction did not indicate thepresence of elements (Z > 9) other than Fe, Cu, Zn,
As, Ag, Hg, Tl and S.
The same fragment was then analysed with a
JEOL 8200 electron microprobe (wavelength dispersive mode, accelerating voltage 15 kV, beam
current 20 nA, beam size 1 µm). Counting times are
20 s for peak and 15 s for background. The
following standards (element, emission line) wereused: Ag metal (AgLα), Cu metal (CuKα), Zn metal(ZnKα), Fe metal (FeKα), cinnabar (HgMα), TlAsS2(TlMα, SKα), As metal (AsLα) and Sb metal(SbLα). Cadmium and Se were sought but were
below the detection limit. The crystal fragment was
found to be homogeneous within analytical error.
Chemical data are given in Table 2.
On the basis of 12 atoms per formula unit
(a.p.f.u.), the chemical formula of ralphcannonite corresponds to Ag0.63(2)Cu0.25(2)Zn1.35(5)Fe0.47(1)Hg0.32(2)Tl0.97(3)[As1.97(6)Sb0.01(1)]Σ1.98(5)S6.03(8).
1092

For the X-ray single-crystal study, the intensity data
were collected using an Oxford Diffraction
Xcalibur 3 diffractometer equipped with a
Sapphire 2 CCD area detector, with MoKα
radiation. The detector-to-crystal distance was
60 mm and 288 frames were collected using ωscan mode, in 0.5° slices, with an exposure time of
45 s per frame. Intensity integration and standard
Lorentz-polarization corrections were performed
with the CrysAlis RED (Oxford Diffraction, 2006)
software package. The program ABSPACK in
CrystAlis RED (Oxford Diffraction, 2006) wasused for the absorption correction. The statisticaltests on the distribution of |E| values (|E 2 – 1| =0.808) and the systematic absences suggested thespace group I 42m. The refined cell parameters are
a = 9.861(2), c = 11.125(3) Å, V = 1081.8(4) Å3.
The crystal structure of ralphcannonite wasrefined starting from the atomic coordinates given
by Bindi (2008) for routhierite, using Shelxl-97(Sheldrick, 2008). Scattering curves for neutral
atoms were taken from the International Tables for
Crystallography (Wilson, 1992). Crystal data anddetails of intensity data collection and refinement arereported in Table 3. Owing to the relatively small
number of observed reflections, only an isotropic
model was refined for ralphcannonite. After several
cycles of refinement, the R1 converged to 0.030,
confirming the validity of the structural model. We
noticed that the goodness-of-fit of the structurerefinement is very low (i.e. 0.289), a feature probably
related to the low-quality diffraction data set.
Four independent cation sites occur in the
crystal structure of ralphcannonite, labelled as Tl,
M1, M2 and As. The M1 and M2 sites correspondto Cu and Hg sites in the crystal structure ofrouthierite (Bindi, 2008; Biagioni et al., 2014a).
The occupancies of these four independent cationsites were refined using the following scattering
curves: Tl site: Tl vs. □; M1 site: Cu vs. □; M2
site: Hg vs. □; As site: As vs. □. The Tl, M1 andAs sites were found to be fully occupied and theirsite occupancies were fixed to 1. At the M2 site,
the refined site-scattering value was 43.9 electrons, compatible with a mixed (Ag,Zn,Fe,Hg)
occupancy. Final atom coordinates and isotropic
displacement parameters are given in Table 4,
whereas selected bond distances are reported inTable 5. The refined and calculated site scattering(in electrons per formula unit, e.p.f.u.) on the basisof the proposed site populations are given in
Table 6. Iron has been considered as divalent, inRALPHCANNONITE, AgZn2TlAs2S6, A NEW MINERAL OF THE ROUTHIERITE ISOTYPIC SERIESTABLE 3. Crystal and experimental data for ralphcannonite.
Crystal data
Crystal size (mm3)
Cell setting, space groupa, c (Å)
V (Å3)Z
Data collection and refinement
Radiation, wavelength (Å)
Temperature (K)2θmax(°)
Measured reflections
Unique reflections
Reflections with Fo > 4σ(Fo)RintRσRange of h, k, l

0.035 x 0.045 x 0.055
Tetragonal, I 42m
9.861(2), 11.125(3)1081.8(4)4MoKα, λ = 0.71073
293
56.05
7722
633
140
0.04080.0498−7 ≤ h ≤ 8,
0 ≤ k ≤ 12,
0 ≤ l ≤ 13
0.02990.04200.104820
0.93 (at 1.94 Å from S2); −1.86 (at 1.19 Å from Tl)

R [Fo > 4σ(Fo)]R (all data)wR (on F 2)
Number of least-squares parameters
Maximum and minimum residual peak (e Å−3)order to achieve electrostatic neutrality; this isconsistent with the observation of Makovicky
et al. (1990) that the presence of Zn and Hg
favours Fe2+ with respect to Fe3+. Finally, Table 7
shows the results of the bond-valence calculations.
Owing to the very small size and amount ofcrystals available, a powder X-ray diffraction
pattern was not collected. Table 8 reports thecalculated powder X-ray diffraction data of ralphcannonite on the basis of the crystallographic datacollected through single-crystal X-ray diffraction.

Crystal structure description
The crystal structure of ralphcannonite is isotypicwith those of routhierite, stalderite and arsiccioite(Graeser et al., 1995; Bindi, 2008; Biagioni et al.,2014a,b), showing a framework formed by two
independent MeS4 tetrahedra sharing corners,
hosting channels parallel to [001]. These channels
contain TlS6 and (As,Sb)S3 polyhedra, sharing
corners and edges with the tetrahedron framework(Fig. 2).

TABLE 4. Atomic coordinates and isotropic displacement parameters (Å2) for ralphcannonite.
Site

Wyckoff site

x/a

y/b

z/c

Uiso

Tl
M1
M2
As
S1
S2

4e
4d
8f
8i
16j
8i

0
0
0.2228(2)0.2611(4)0.0943(6)0.1257(7)0½½0.2611(4)0.3308(7)0.1257(7)0.3524(2)¼½0.2587(6)0.3743(7)0.1295(9)0.0413(7)0.0334(14)0.0405(11)0.0400(12)0.037(2)0.040(3)1093

LUCA BINDI ET AL.

TABLE 5. Selected bond distances (in Å) in
ralphcannonite.
–S2–S1
average
As –S1–S2
averageTl

3.037(10) × 2 M1 –S1
3.401(7) × 4
3.280
2.198(8) × 2 M2 –S1
2.374(11)–S2
2.257
average

2.358(7) × 4
2.417(6) × 2
2.519(7) × 2
2.468

As stated above, four independent cation sites
occur. The two independent tetrahedral sites, M1
and M2, have average bond distances of 2.358 and2.468 Å, respectively. The <M1–S> bond distanceagrees closely with that observed by Graeser et al.
(1995) for the Cu site of stalderite, i.e. 2.357(4) Å,
whereas the M2 site of ralphcannonite is enlarged
with respect to the corresponding Zn site ofstalderite, having an average bond distance of
2.406 Å. This is in agreement with the replacementof the small Zn (and possibly Cu) atoms by thelarger Ag at the M2 site.

The As site forms a trigonal pyramid with three S
atoms, with an average bond distance of 2.257 Å.
The refinement of the site occupancy points to thefull occupancy of this site by arsenic, in agreementwith chemical data showing only a negligible
amount of Sb (0.01 a.p.f.u.). Actually the
AsS3 geometry is distorted, with two relatively
short As–S1 bond distances (2.198 Å) and a longer
one (2.378 Å).
The coordination of the Tl site can be described
as an orthorhombic pyramid with a split apex, asin the other members of the routhierite isotypicseries. On the other site of the pyramidal split apex,
a relatively short Tl–Tl distance occurs, i.e.
3.284(4) Å. This value agrees perfectly with thatreported for stalderite (3.28 Å) by Graeser et al.
(1995) and is in the range of Tl–Tl distances
observed in other members of the routhierite group,i.e. 3.33 Å and 3.47 Å for routhierite from Monte
Arsiccio and Jas Roux, respectively (Bindi, 2008;
Biagioni et al., 2014a) and values ranging between
3.25 and 3.51 Å for the split Tl site in arsiccioite(Biagioni et al., 2014b). As reported by previous
authors, such short Tl–Tl distances most likely
indicate some type of Tl–Tl interaction.

TABLE 6. Refined site-scattering values (e.p.f.u.), assigned site population (a.p.f.u.) and comparison between
observed and calculated bond distances (in Å) at M1, M2 and As sites in ralphcannonite.
Site

XRD

EPMA

Site population<Me–S > obs<Me–S > calc

M1
M2
As

29.0
43.8
33.0

29.8
42.4
33.1

[Zn0.751Cu0.249]*
Ag0.317Zn0.290Fe0.234Hg0.159[As0.995Sb0.005]*

2.358
2.468
2.257

2.352
2.499
2.261

XRD –X-ray diffraction; EPMA – electron probe microanalysis.
*Values normalized to 1

TABLE 7. Bond-valence sums (BVS, in valence units) calculated using the parameters given by Brese andO’Keeffe (1991).
M1
S1
S2
Σ cations
Theoretical

M2
x4

0.43
1.72
1.75

Tl
x2

0.51
2x
0.39x2
1.80
1.68

Σ anions

As
x4

0.12
0.34x2
1.16
1.00

x2

1.17
0.74
3.08
3.00

2.23
1.86

Note: In mixed sites, the bond-valence contribution of each cation has been weighted according to its occupancy (seeTable 6). Left and right superscripts indicate the number of bonds involving cations and anions, respectively.

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RALPHCANNONITE, AgZn2TlAs2S6, A NEW MINERAL OF THE ROUTHIERITE ISOTYPIC SERIES

Graeser et al. (1995) proposed that in stalderite
the small M1 site is occupied by Cu+, whereas thedivalent cations (Zn2+ and minor Fe2+ and Hg2+)
are hosted at the larger M2 site. On the contrary, theresults of the crystal structure study suggest that M1
is preferentially occupied by Zn2+, whereas M2
hosts the larger cations Ag+ and Hg2+, replaced by
Zn2+ and Fe2+. As reported by Biagioni et al.
(2014b) for arsiccioite, the cation distribution
among the M1 and M2 sites is guided by thesteric constraint that prevails over the valence state.
Therefore, the largest cation, Ag+ is hosted at thelarge M2 site, whereas Zn2+, the smallest cation,
preferentially occupies the M1 site.
Similarly to the ideal formula of arsiccioite,
M1
HgM2(Ag0.5Hg0.5)2TlAs2S6, the formula ofralphcannonite could be written as M1ZnM2(Ag0.5
Zn0.5)2TlAs2S6. The Ag content of ralphcannonite
is actually a little lower than the ideal one, and its
deficit is probably balanced through the heterovalent substitution M1Zn2+ + M2Ag+ → M1Cu+ +M2(Zn,Fe,Hg)2+.

TABLE 8. Calculated powder X-ray diffraction data forralphcannonite. Intensity and dhkl were calculatedusing the software Powdercell 2.3 (Kraus and Nolze,
1996) on the basis of the structural model given in
Table 4; only reflections with Icalc > 5 are listed. The
five strongest reflections are given in bold.
Icalc

dcalc

hkl

Icalc

dcalc

hkl

8
9
85
12
40
17
100
20
17
24
39
11
6

6.973
4.930
4.100
3.486
3.471
3.118
2.954
2.656
2.583
2.465
2.460
2.422
2.338

110
200
211
220
103
310
222
321
114
400
303
204
411

5
8
14
10
10
15
13
9
9
6
6
7
11

2.324
2.201
2.076
2.010
1.845
1.807
1.743
1.741
1.728
1.604
1.594
1.588
1.501

330
323
314
413
404
521
440
433
424
611
316
514
622

Bond-valence balance

Nomenclature of the routhierite isotypic series

Bond-valence sums (BVS), according to Brese andO’Keeffe (1991), are reported in Table 7, on thebasis of the site population given in Table 6.
With respect to the BVS of routhierite andarsiccioite, where differences up to 25% between
observed and calculated BVS have been reported(Biagioni et al., 2014a,b), only minor deviations
from the expected values (up to 7% for the M2 site)
have been observed, confirming the validity of the
proposed site population. A good agreement
between observed and calculated BVS also occurs
for the As site. The BVS excess for the Tl atom issimilar to that reported in arsiccioite and routhierite(Biagioni et al., 2014a,b) and can be related to theoverestimation of the bond parameter tabulated by
Brese and O’Keeffe (1991) for the pair (Tl,S), i.e.
2.63 Å, as suggested by Biagioni et al. (2014b).
Using a value of RTl,S = 2.55 Å, a BVS of 0.95
valence units (v.u.) can be calculated for the Tl site.
Crystal chemistry
Structural formula
The crystal-chemical formula of ralphcannonite canbe written as M1(Zn0.75Cu0.25)M2(Ag0.32Zn0.29Fe0.23
Hg0.16)2TlAs2S6, with the relative error of thevalence equilibrium Ev = +0.9.
1095

The general crystal-chemical formula of themembers of the routhierite isotypic series
2++
can be written as (Me +1–2xMe 2+
2x )(Me 1–xMe x )2Tl(As1–ySby)2S6, with 0 ≤ x ≤ 0.5 and y < 0.5. The
cation Me + is represented by Cu+ and Ag+, whereas
bivalent cations Me 2+ are Zn2+, Hg2+ and Fe2+.
Minor Cd2+ (up to 0.02 a.p.f.u.) has been reported
in arsiccioite (Biagioni et al., 2014b).
The crystal-structure studies of arsiccioite andralphcannonite indicate that Ag prefers the largest
M2 site; this observation can also be extended toAg-bearing routhierite (e.g. specimen from Monte
Arsiccio – Biagioni et al., 2014a,b). On thecontrary, the smaller cations (Zn2+, Cu+) are
preferentially hosted at the M1 site.
Graeser et al. (1995), in their study of stalderite,
proposed the site population M1 = Cu1.00 and M2 =Zn0.55Fe0.25Hg0.20; however, as pointed out by
Biagioni et al. (2014b), a site population with M1 =Zn1.00 and M2 = Cu0.50Fe0.25Hg0.20Zn0.05 cannot be
excluded, resulting in very similar site-scatteringvalues, BVS and calculated average bond distances.
Consequently, one could also verify a different cation
distribution for ralphcannonite, with Zn completely
hosted at the M1 site and a mixed (Ag,Cu,Fe,Hg,Zn)
occupancy at the M2 site. In this case, the idealizedsite population should be M1 = Zn1.00 and M2 =Ag0.32Cu0.13Fe0.23Hg0.16Zn0.16. Assuming such a

LUCA BINDI ET AL.

Consequently, the same chemistry could correspondto two different crystal-chemical formulae. Taking
into account this issue, in our opinion, the classification of the members of the routhierite isotypic series
should be based on the chemical data only, taking into
account the combination of dominant Me+ and Me2+
cations. In this way the following species can be
defined (Fig. 3): (1) routhierite – Me+ = Cu+, Me 2+ =Hg2+; (2) stalderite – Me+ = Cu+, Me2+ = Zn2+; (3)arsiccioite – Me+ = Ag+, Me2+ = Hg2+; (4) ralphcannonite – Me+ = Ag+, Me 2+ = Zn2+, being the generalchemical formula Me+Me 2+
2 TlAs2S6.

Relationships between the crystal chemistry of‘routhierites’ and the ore geochemistry

FIG. 2. Crystal structure of ralphcannonite, as seen down[001] (a) and [010] (b). Polyhedra: green: M1 tetrahedra;
light blue: M2 tetrahedra. Circles: grey: Tl site; violet: As
site; yellow: S1 site; orange: S2 site.

distribution, the BVS, average bond distances andcalculated site scattering are similar to those proposedin Table 6, suggesting that the actual site occupancy,
by using conventional X-ray diffraction, cannot beknown, owing to the similar values of the scatteringfactors for Cu, Zn and also Fe. It is noteworthy that thesite population proposed in Table 6 would correspondto the ideal formula Zn(Ag0.5Zn0.5)2TlAs2S6, whereas
in the alternative cation distribution the formula
should be written as Zn(Ag0.5Fe0.5)2TlAs2S6, with
Fe2+ being the dominant bivalent cation at M2.
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The members of the routhierite isotypic series arevery rare minerals. Well-characterized specimens ofrouthierite have only been reported so far from Jas
Roux, France and the Monte Arsiccio mine, Italy(Johan et al., 1974; Biagioni et al., 2014a). The
other three phases have only been reported
from their type localities, Monte Arsiccio mine(arsiccioite – Biagioni et al., 2014b) and theLengenbach quarry (stalderite – Graeser et al.,
1995; ralphcannonite – this work).
These minerals can have a complex chemistry,
being characterized by the occurrence of Tl, As, Cu,
Ag, Hg, Zn and minor Fe and Sb. In particular, thechemical variability of the tetrahedral cations (Cu,Ag, Hg, Zn and Fe) seems to be closely related tothe ore geochemistry, as discussed by Biagioni
et al. (2014b) for the pair routhierite-arsiccioite
from Monte Arsiccio. This locality, as well as Jas
Roux, are characterized by a relatively large
abundance of Hg, as evidenced by the occurrenceof the Hg members of the routhierite isotypic series,
as well as other Hg phases, i.e. aktashite,
Cu6Hg3As4S12 and laffittite, AgHgAsS3 (Favreau
et al., 2011; Biagioni et al., 2014c).
The ore geochemistry at the Lengenbach quarry,on the contrary, seems to be Hg-depleted. In fact,
the Zn-dominant (sometimes Fe-enriched)members of the routhierite isotypic series occur
there, stalderite and ralphcannonite. In addition, theZn isotype of aktashite, nowackiite, Cu6Zn3As4S12,
has been identified (Marumo and Burri, 1965). The
variable Ag/Cu ratio within the crystallizing
medium controls the crystallization of the stalderite-ralphcannonite pair, as well as other isotypiccompounds described from the Lengenbach
quarry, e.g. hatchite, AgTlPbAs2S5 and wallisite,
CuTlPbAs2S5.

RALPHCANNONITE, AgZn2TlAs2S6, A NEW MINERAL OF THE ROUTHIERITE ISOTYPIC SERIES

FIG. 3. Ag/(Ag + Cu) versus Hg/(Hg + Zn + Fe) atomic ratios in the routhierite isotypic series. Open triangles: arsiccioite
from Monte Arsiccio mine (Biagioni et al., 2014b). Filled triangles: routhierite from Monte Arsiccio mine (black,
Biagioni et al., 2014b; grey, Biagioni et al., 2014a). Open circles: routhierite from Jas Roux (Johan et al., 1974). Filled
circles: routhierite from Jas Roux (Bindi, 2008). Open squares: stalderite from Lengenbach (Graeser et al., 1995). Filledsquares (red): ralphcannonite (this work). Filled lozenges: ’Sb-routhierite’ from Hemlo (Harris, 1989).

Conclusion
The description of ralphcannonite increases theknowledge about the crystal chemistry of therouthierite isotypic series, bringing new data to
the systematics of thallium sulfosalts. The unexpected cation distribution described by Biagioni
et al. (2014b) in arsiccioite has been confirmed,
with Ag, the largest cation, preferentially hosted at
the largest M2 site: the priority of the steric effectover the valence state in the members of therouthierite isotypic series is thus confirmed.

Acknowledgements
The research was supported by “progetto d’Ateneo
2012. Università di Firenze” to LB.

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