Mineralogical Magazine, August 2016, Vol. 80(5), pp. 819–840

Argentobaumhauerite: name, chemistry, crystal structure,comparison with baumhauerite, and position in the
Lengenbach mineralization sequence
DAN TOPA1,* AND EMIL MAKOVICKY2
1
2Natural History Museum-Wien, Burgring 7, 1010 Wien, Austria
Institute for Geoscience and Mineral Resources Management, University of Copenhagen, Østervoldgade 10,
DK-1350, Copenhagen K, Denmark[Received 24 July 2014; Accepted 28 August 2015; Associate Editor: Sergey Krivovichev]
ABSTR ACTThe crystal structure of argentobaumhauerite is reported for the first time from a sulfosalt aggregate from
Lengenbach deposit, Binntal, Switzerland. The chemical formula of argentobaumhauerite, calculated inagreement with the results of structure determination is Cu0.06Ag1.20Tl0.18Pb21.46Sb0.56As32.28S72.26. The
difference from the idealized baumahuerite formula, Pb12As16S36, and from the formula of Ag-, Tl- and Sbfree baumhauerite from Moosegg, Austria, Pb11.80As16.28S35.92, expresses the Ag + As and Tl + As
substitution for 2Pb. Argentobaumhauerite is triclinic, a = 7.9053(10), b = 8.4680(10), c = 44.4102(53) Å,
α = 84.614(2), β = 86.469(2), γ = 89.810(2)°. V(cell) = 2954.16 Å3, space group P1. Baumhauerite
Pb11.80As16.28S35.92 from Moosegg is triclinic, a = 7.884(4), b = 8.345(4), c = 22.811(11) Å, α =90.069(8), β = 97.255(8), γ = 90.082(8)°, V(cell) = 1488.8(13) Å3, space group P1. Both minerals represent
the N1,2 = 3;4 = 3.5 member of the sartorite homologous series, with As-rich slabs separated by zigzag
layers of trigonal coordination prisms of lead. In argentobaumhauerite the sequence of alternating N = 3 andN = 4 slabs of baumhauerite is further modified by alternation of two distinct types of N = 4 slabs, those with
Pb present in the slab interior and those with the interior Pb substituted by Ag + As. The length andarrangement of crankshaft chains of short As–S bonds differs between different slabs, and especiallybetween the N = 4 slabs of baumhauerite and argentobaumhauerite. The name ‘argentobaumhauerite’
replaces the preliminary name ‘baumhauerite-2a’ (IMA-CNMNC; accepted proposal 15-F).
K E Y WO R D S : baumhauerite, argentobaumhauerite, crystal structure, Ag + As substitution, Tl + As substitution,mineralization sequence, Lengenbach.
Introduction
BAUMHAUERITE was discovered by Solly (1902) in amaterial from Lengenbach (Binntal, Switzerland)and named for the Freiburg professor Baumhauer
who dedicated himself to the study of Lengenbachminerals. Baumhauerite is a Pb-As sulfosalt, a
member of the sartorite homologous series.
According to Makovicky (1985) this is a combinatorial series (Makovicky 1997a,b), in which only

*E-mail: dan.topa@nhm-wien.ac.at
DOI: 10.1180/minmag.2016.080.025© 2016 The Mineralogical Society

the members N = 3 and N = 4 are known, and thevariety is created by combinations of these two unit
homologue slabs in different ratios. Baumhaueriteis the simplest of these combinations, namely
N1,2 = 3;4.
The combined thickness of the alternating N = 3
and N = 4 slabs leads to the (010) spacing of ∼22 Å
for baumhauerite (Engel and Nowacki, 1969). The
complications started by the discovery of two‘baumhauerite varieties’, respectively silver-poorand silver-rich, by Laroussi et al. (1989). The
discovery that the Ag-rich baumhauerite has adoubled a parameter, equal to 44.7 Å, by means of
single-crystal X-ray photographs, confirmed by

DAN TOPA AND EMIL MAKOVICKY

electron diffraction, by Pring et al. (1990), was afurther surprising complication of the baumhauerite
problem. They suggested a monoclinic unit cellwith a = 44.74, b = 8.477, c = 7.910 Å and β =93.37° with a possibility left open for a triclinic
structure with α and γ close to 90° and named it‘baumhauerite-2a’. Two models are in agreementwith the large unit cell – the N1–4 = 3;4;3;4 model or
the N1–4 = 3;3;4;4 model – but which one corresponds to the structure of the mineral? In the firstvariation, what is the nature of the difference
between the two consecutive 3;4 modules? Is it adifferentiation of Pb, As and Ag as it was in generalterms suggested by Pring et al. (1990)?
Pring and Graeser (1994) re-examined the
problem more accurately and they suggest thatbaumhauerite is a polytypic series, with the ‘2a’member displaying a sequence of baumhaueritelike cells in which alternating cells are ‘inverted
about the b (i.e. 8 Å) repeat’, whereas theunsubstituted baumhauerite has a sequence ofcells without inversion. A new phase which theyobserved and studied by high-resolution transmission electron microscopy (HRTEM) and electron
diffraction, ‘3abc’, was interpreted by them as a‘normal-normal-reversed’ sequence of ‘baumhauerite cells’. The presence of cation substituents,
especially Ag, should help to stabilize thesepolytypes. Besides giving an overall picture of thesartorite homologous series, as seen via HRTEM,
Pring (2001) essentially summarizes the existingobservations on baumhauerites.
The samples studied in the present work comefrom material collected between 1850 and 2011 at
the Lengenbach quarry, Binntal, Switzerland.
Altogether 152 samples were made available to us
by the following persons (in chronological order):Peter Berlepsch (Switzerland), Horst Geuer(Germany), Frank Keutsch (Germany), Uwe
Kolitsch (Austria), Thomas Raber (Germany),
Phillippe Roth (Switzerland) and Ralph Cannon(Germany) from their private collections. As
curator of the mineralogical collection, Uwe
Kolitsch also provided selected material from 11
samples from the mineralogical collection of the
Natural History Museum Vienna. The locality of
the comparative material of substitution-free Pb-As
baumhauerite is Moosegg by Golling, Salzburg
Land, Austria, provided to the first author by Prof.
Elisabeth Kirchner (Austria) in the mid 1990s, withchemistry and unit-cell parameters provided for the
first time by Graeser et al. (1986).
The present study, especially because of thecomplete crystal structure determinations it

contains, explains some of the previous observations and corrects some of their conclusions. The
crystal structure of argentobaumhauerite is here
compared with the refined structure of Ag-, Tl-, Sbfree baumhauerite. It also brings new knowledge
concerning both the chemistry and deposition
sequence of the sartorite homologues at the type
locality of Lengenbach and the general features of
the homologous series type of highly covalent andlone electron pairs (LEP).
The nomenclature voting proposal 15-F
‘Renaming of baumhauerite-2a to argentobaumhauerite’ was approved by the Commission on New
Minerals, Nomenclature and Classification(CNMNC) of the International Mineralogical
Association (IMA) by a vote 13-1 on May 13,
2015, stating that the independent status ofargentobaumhauerite as a mineral species isbeyond any doubt, based on its composition,
symmetry, a detailed crystal structure and a clear
compositional gap against baumhauerite.

Mineral chemistry820

Up to twenty separate grains, depending on
quantity of available material in a sample, werepre-lifted from the dolomite-based gangue containing sulfosalt aggregates and were embedded in anaraldite mount, polished and studied in reflected
light and examined by qualitative (back-scattersecondary electron (BSE) images and energydispersive spectroscopy analyses) and quantitative(wavelength-dispersive spectroscopy) electron
microprobe analyses. This procedure was separately
applied to all 152 samples.
Argentobaumhauerite, baumhauerite and theassociated sulfosalts were analysed using a JEOLHyperprobe JXA-8530F electron microprobe(installed at Natural History Museum, Vienna,
Austria) operated at 25 kV and 20 nA, with abeam diameter of 2 µm. Wavelength-dispersion
data were collected using the following standards
and emission lines: galena (PbMα), chalcopyrite(CuKα), Ag metal (AgLα), stibnite (SbLα), cinnabar (HgLα) and lorandite (TlLα, AsLα, SKα). The
raw data were corrected for matrix effects with the
JEOL on-line ZAF correction. The results of theelectron microprobe analyses for baumhauerite andargentobaumhauerite are compiled in Table 1.
Chemical data for associated sartorite homologues
are not discussed in detail here, being the subject ofother, separate, publications but are used for binary
and ternary plots.

ARGENTOBAUMHAUERITETABLE 1. Chemical data for the crystals investigated.
No.* Sample

NA1

5 0.04(01) 1.38(08) 0.40(03) 47.38(13) 0.05(09) 0.72(05) 25.80(12) 24.72(02) 100.49(24)23argentobaumhauerite(Binn)
baumhauerite (Binn)baumhauerite(Moosegg)

Cu

Ag

Tl

Pb

Hg

Sb

As

S

total

4 0.02(01) 0.14(04) 0.39(04) 51.44(20) 0.06(05) 0.45(04) 23.74(04) 23.34(09) 99.58(16)450.93(09)25.40(09) 24.00(09) 100.33(05)*[1] Cu0.06Ag1.20Tl0.18Pb21.46As32.28Sb0.56S72.26 ΣAg + Tl + Cu = 1.44, ΣAs + Sb = 32.84, Nchem = 3.55, Agsubs = 29.1,
Tlsubs = 1.5, ch = –1.29, ev = –1.14[2] Cu0.01Ag0.06Tl0.09Pb12.23As16.28Sb0.18S35.82 ΣAg + Tl + Cu = 0.16, ΣAs + Sb = 15.77, Nchem = 3.61, Agsubs = 2.9,
Tlsubs = 1.4, ch = 0.48, ev = 0.43
[3] Pb11.80As16.28S35.92 Ncalc = 3.45, Agsubs = 0, Tlsubs = 0, ch = 0.91, ev = 0.81
The compositions are expressed in wt.%. NA = number of analyses. Standard deviation for the last digit is shown inparentheses. The Nchem represents chemical calculated sartorite homologue number defined by Makovicky (1985) andAgsubs, Tlsubs represent Ag and Tl substitution defined by Makovicky and Topa (2015). The parameters ch and ev express
the absolute and relative error in the charge balance based on the sum of cation and anion charges.

The chemical formula of argentobaumhauerite
from the Lengenbach quarry, calculated in agreement with the results of structure determination is
Cu0.06Ag1.20Tl0.18Pb21.46Sb0.56As32.28S72.26. The
difference against the idealized baumhauerite
formula, Pb12As16S36, and against the formula ofsubstitution-free baumhauerite from Moosegg,
Pb11.80As16.28S35.92, expresses the Ag + As andTl + As substitution for 2Pb.
The homologue order Nchem, calculated forargentobaumhauerite from the results of chemical
analysis according to the procedure given by
Makovicky (1985) and Makovicky and Topa(2015), is 3.55, close to the structural value of
3.5. The percentage of the (Tl + (As,Sb)) substitution for 2Pb, in relation to a hypotheticalend-member in which all Pb has been eliminated,is only 1.5%. The percentage of the (Ag + (As,Sb))substitution for 2Pb, however, is very large,
calculated as 29.1% of the theoretically possible
substitution (which, unlike Tl, preserves the Pbsites in the trigonal coordination prisms).
Electron microprobe analyses of the studied
samples of baumhauerite from Lengenbach, whichis associated with argentobaumhauerite (Table 1)
give N = 3.61, 1.4% of (Tl + (As,Sb)) substitution,and only 2.9% of (Ag + (As,Sb)) substitution for
2Pb. So, in principle, the typical baumhauerite is anunsubstituted or minimally substituted sartorite
homologue N = 3.5.
Electron microprobe analysis of baumhauerite
from Moosegg (Table 1) indicates that it is apure Pb-As sulfosalt, Pb11.80As16.28S35.92, Ncalc
821= 3.45, without antimony, thallium and silver. This
makes its crystal structure doubly interesting,because it allows one to investigate and specify
unambiguously the nature of mixed cation
positions, which is often not possible in casesof complex Pb-Tl-Ag-As-Sb compositions. Thisis also valuable for resolving the mixed positions
in argentobaumhauerite.
When we compare our results with the publisheddata, Laroussi et al. (1989) found between 1.4 and2.1 wt.% Ag and 0 to 0.8 wt.% Tl in ‘Ag-richbaumhauerite’; one analysis is given as Pb10.54
Ag0.65Tl0.10As16.68S36. In comparison, they foundup to 0.8 wt.% Ag and 0.9 wt.% Tl; with Sb below
0.5 wt.%, in baumhauerite itself. They state that
‘Ag-rich baumhauerite’ forms ‘lamellar intergrowth’ with baumhauerite. Pring et al. (1990)
found the average composition of baumhauerite-2a(now argentobaumhauerite) to be Pb11Ag0.7As17.2
Sb0.4S36, whereas the surrounding baumhauerite
was Pb12As17.2S36. The 2a phase occurred asirregular to flame-like inclusions in normal baumhauerite. Although there is no trace of diffuse
streaking in the electron diffraction photographs ofthe baumhauerite varieties, Pring et al. (1990)
demonstrate intergrowths of the two phases almost
on a unit-cell level.
A compositional puzzle is represented by the
structurally examined baumhauerite of Engel andNowacki (1969), with symmetry and structure ofbaumhauerite but composition (Pb11.6As15.7
Ag0.6S36) of argentobaumhauerite. The puzzle
can be solved by inspecting their electron

DAN TOPA AND EMIL MAKOVICKYTABLE 2. Single-crystal X-ray diffraction: experimental and refinement details.
Crystal data
Chemical formula
Structural formula
Chemical formula weight
Cell setting
Space group
a (Å)
b (Å)
c (Å)
α,β,γ (°)V(Å3)
Z
Dx (mg m–3)
No. of reflections for cell param.
µ (mm–1)
Crystal form
Crystal size (mm)Crystal colour
Data collection
Tmin
Tmax
No. of measured refl.
No. of independent refl.
No. of obs. refl.
Criterion for obs. refl.
Rint, Rσ (%)θmax(°)
Range of h, k, lRefinement
Refinement on Fo2
R[Fo > 4σ(Fo)] (%)
wR(Fo2)(%)
S (Goof)No. of refl. used in refinement
No. of parameters refined
Weighting scheme

argentobaumhauerite (Binntal)
Cu0.06Ag1.20Tl0.18Pb21.46As32.28Sb0.56S72.26
Ag1.61(Pb,Tl)20.75As33.18Sb0.46S72
9406
Triclinic
P1
7.905(1)8.468(144.410(5)84.614(2), 86.496(2), 89.810(2)2954.2(6)
1
5.29
7018
41.29
irregular
0.05 × 0.07 × 0.13
black

baumhauerite (Moosegg)
Pb11.80As16.28S35.92
Pb12.14As15.86S36
4839.2
Triclinic
P1
7.884(4)8.345(4)22.811(12)90.069(8), 97.255(8), 90.082(8)1488.8(13)
1
5.4
3217
43.89
irregular
0.05 × 0.06 × 0.16
black

0.13020.440925,6658445
6545
I > 2 (I)7.09, 6.27
23.28
–8 < h < 8, –9 < k < 9, –49 < l < 49

0.1496
0.4147
9902
6137
5385
6.13, 8.46
20.96
–7 < h < 7, –8 < k < 8, –22 < l < 22

3.94
5.00
5.66
5.74
0.995
1.00
8445
6137
583
582
w = 1/[σ2(Fo2) + (0.0318P)2 + 0.0P]w = 1/[σ 2(Fo2) + (0.0464P)2 + 0.0P]
where P = (Fo2 + 2F2c )/3
0.001
0.003
(Δ/σ)max
Δρmax (e/Å3)
3.46 [0.94 Å from Pb11]
1.37 [0.96 Å from As17]–3.40 [0.87 Å from Pb11]–1.29 [0.91 Å from As17]
Δρmin (e/Å3)
Extinction method
none
none
Source of atomic scattering factors: International Tables for Crystallography (1992, Vol. C, Tables 4.2.6.8 and 6.1.1.4)
Computer programs
Structure solution
SHELXS97 (Sheldrick, 1997a)
Structure refinement
SHELXL97 (Sheldrick, 1997b)

microprobe data – only one analysis gave
measurable Ag contents – and the total ensembleof four analyses suggests an unrecognizedinclusion of argentobaumhauerite in a baumhauerite matrix. Thus, the material investigated
was most probably as heterogeneous as that of
the other investigators.

Crystallography, diffraction data collection
and crystal structure analysis

822

For data collection (Table 2), fragments withirregular shape, removed from pre-analysed polishedsections, were mounted on a Bruker AXS threecircle diffractometer equipped with a CCD area

ARGENTOBAUMHAUERITETABLE 3a. Atom positions, occupancies (sof) and equivalent displacement parameters (Å2) for
argentobaumhauerite.
Atom

sof

x

y

z

Ueq

Pb1
Pb2
Pb3
Pb4
Pb5
Pb6
Pb7
Pb8
Pb9
Pb10
Ag
Pb11
As1
Sb
As2
As3
As4
As5
As6
As7
As8
As9
As10
As11
As12
As13
As14
As15
Pb12
As16
As17
S1
S2
S3
S4
S5
S6
S7
S8
S9
S10
S11
S12
S13
S14
S15
S16
S17
S18
S19
S20

1
1
1
1
1
1
1
1
1
1
0.737(6)0.263(6)0.745(14)0.255(14)
1
1
1
1
1
1
1
1
1
1
1
1
1
0.814(6)0.186(6)
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1

0.28586(8)0.27922(8)0.19559(9)0.21902(8)0.01163(7)0.30778(8)0.29141(10)0.21333(8)0.21472(10)0.42344(8)0.05805(15)0.05805(15)0.0047(3)0.0047(3)0.3529(2)0.31844(19)0.3344(2)0.3202(2)0.2420(2)0.23543(19)0.07801(19)0.41758(18)0.42746(18)0.27809(18)0.25538(17)0.20103(18)0.18468(18)0.4864(2)0.4864(2)0.15130(18)0.1458(2)0.1706(5)0.1930(5)0.4947(5)0.4803(5)0.1864(5)0.1362(5)0.1475(5)0.1546(5)0.4507(5)0.4449(5)0.0747(4)0.0564(5)0.5927(5)0.3891(4)0.3088(5)0.2669(4)0.0841(5)0.0592(5)0.4352(4)0.4310(4)0.41736(7)0.90572(7)0.58361(8)0.06641(7)0.72531(7)0.71939(7)0.21271(8)0.30861(7)0.80917(8)0.15308(7)0.62524(13)0.62524(13)0.0954(2)0.0954(2)0.1856(2)0.62005(17)0.84916(17)0.3007(2)0.1858(2)0.69897(16)0.77390(16)0.49937(16)0.08541(17)0.01650(16)0.45315(16)0.86874(17)0.42674(16)0.6337(2)0.6337(2)0.09072(16)0.6518(2)0.3198(4)0.9187(5)0.5702(5)0.8316(4)0.1728(4)0.6172(5)0.6503(5)0.0600(4)0.8334(4)0.3183(4)0.1771(4)0.6756(4)0.5063(4)0.9143(4)0.8065(4)0.2566(4)0.0231(4)0.4166(4)0.3027(4)0.7140(4)0.877946(15)0.882129(15)0.168905(16)0.167892(15)0.739939(13)0.333626(14)0.333237(16)0.614997(14)0.613496(17)0.459424(14)0.04284(3)0.04284(3)0.03571(6)0.03571(6)0.97911(4)0.96874(3)0.08611(4)0.07944(4)0.80325(4)0.80925(3)0.24424(3)0.25375(3)0.24639(3)0.69074(3)0.69665(3)0.41665(3)0.41078(3)0.46402(6)0.46402(6)0.53384(3)0.52500(4)0.00778(10)0.01224(11)0.04357(12)0.94792(9)0.93890(9)0.93123(9)0.09754(9)0.09267(10)0.13132(9)0.12290(8)0.84672(8)0.85111(9)0.18093(9)0.82137(8)0.21110(9)0.21759(8)0.77619(9)0.77876(8)0.72518(8)0.72794(9)0.03397(17)0.03181(17)0.04255(19)0.03392(17)0.02460(16)0.02952(16)0.0439(2)0.02870(16)0.0472(2)0.03036(17)0.0463(5)0.0463(5)0.0732(10)0.0732(10)0.0386(5)0.0243(4)0.0263(4)0.0369(4)0.0348(4)0.0207(3)0.0210(4)0.0170(3)0.0220(4)0.0176(3)0.0172(3)0.0219(4)0.0183(3)0.0871(11)0.0871(11)0.0193(3)0.0383(5)0.0307(10)0.0377(11)0.0411(12)0.0286(10)0.0248(9)0.0326(10)0.0319(10)0.0295(10)0.0265(9)0.0216(9)0.0207(8)0.0232(9)0.0219(9)0.0173(8)0.0246(9)0.0193(8)0.0256(9)0.0217(9)0.0200(8)0.0239(9)(continued)

823

DAN TOPA AND EMIL MAKOVICKYTABLE 3a. (contd.)
Atom

sof

x

y

z

Ueq

S21
S22
S23
S24
S25
S26
S27
S28
S29
S30
S31
S32
S33
S34
S35
S36

1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1

0.1958(4)0.2307(4)0.1084(4)0.1100(4)0.4511(4)0.4211(4)0.0661(4)0.0420(4)0.3583(4)0.3685(4)0.0042(5)0.0084(5)0.3576(4)0.3197(5)0.3152(5)0.3004(5)0.4767(4)0.0155(4)0.2387(4)0.8303(4)0.0466(4)0.5191(4)0.9313(4)0.4512(4)0.6476(4)0.2404(4)0.7111(4)0.1202(4)0.0758(4)0.5992(4)0.8287(4)0.4222(5)0.28884(8)0.28370(8)0.68158(8)0.67692(8)0.64835(8)0.65488(8)0.37449(8)0.36822(8)0.40094(9)0.39803(8)0.44417(9)0.44711(9)0.56689(9)0.56313(8)0.49581(9)0.49411(10)0.0200(8)0.0188(8)0.0171(8)0.0196(8)0.0203(8)0.0201(8)0.0200(8)0.0208(8)0.0210(9)0.0207(8)0.0219(9)0.0265(9)0.0224(9)0.0223(9)0.0245(9)0.0330(10)TABLE 3b. Atom positions, occupancies (sof) and equivalent displacement parameters (Å2) for
baumhauerite.
Atom
Pb1
Pb2
Pb3
Pb4
As17
Pb5
Pb6
Pb7
Pb8
Pb9
Pb10
Pb11
Pb12
As1
As2
As3
As4
Pb14
As5
Pb13
As6
As7
As8
As9
As10
As11
As12

Pb
Pb
Pb
Pb
As
Pb
Pb
Pb
Pb
Pb
Pb
Pb
Pb
As
As
As
As
Pb
As
Pb
As
As
As
As
As
As
As

sof

x

y

z

Ueq

1
1
1
0.636(11)0.364(11)
1
1
1
1
1
1
1
1
1
1
1
0.651(11)0.349(11)0.853(11)0.147(11)
1
1
1
1
1
1
1

−0.0089(2)0.9808(2)0.6984(2)0.1937(3)0.1937(3)0.8984(2)0.6244(2)0.6067(2)0.1532(2)0.1507(2)0.5486(2)0.4349(2)0.4629(2)0.4466(5)0.4177(5)0.1616(6)0.7637(5)0.7637(5)0.8573(6)0.8573(6)0.4633(5)0.4542(5)0.1563(5)0.1791(5)0.7468(5)0.7372(5)0.4959(5)0.01268(18)0.51434(19)0.49627(18)0.7219(3)0.7219(3)0.24084(18)0.26403(19)0.75861(18)0.2583(2)0.76478(18)0.28028(18)0.01816(18)0.52600(19)0.2002(4)0.7548(5)0.2602(5)0.9794(4)0.9794(4)0.7360(5)0.7360(5)0.0126(5)0.4314(4)0.9421(4)0.5029(4)0.0132(4)0.5662(4)0.7633(4)0.99844(8)0.99023(8)0.15199(8)0.19332(13)0.19332(13)0.32219(8)0.46932(9)0.46830(8)0.57444(9)0.57357(8)0.71480(8)0.89209(8)0.89826(8)0.06198(17)0.04936(19)0.1662(2)0.15896(14)0.15896(14)0.2978(2)0.2978(2)0.30790(18)0.29319(19)0.40859(18)0.41934(19)0.61743(19)0.62761(18)0.74489(19)0.0294(5)0.0358(5)0.0277(5)0.0493(12)0.0493(12)0.0250(4)0.0380(5)0.0273(5)0.0377(5)0.0287(5)0.0238(4)0.0343(5)0.0385(5)0.0179(10)0.0202(10)0.0256(11)0.0471(15)0.0471(15)0.050(2)0.050(2)0.0182(10)0.0225(10)0.0180(10)0.0173(10)0.0185(10)0.0172(10)0.0198(10)(continued)

824

ARGENTOBAUMHAUERITETABLE 3b. (contd.)
Atom
As13
As14
As15
As16
S1
S2
S3
S4
S5
S6
S7
S8
S9
S10
S11
S12
S13
S14
S15
S16
S17
S18
S19
S20
S21
S22
S23
S24
S25
S26
S27
S28
S29
S30
S31
S32
S33
S34
S35
S36

As
As
As
As
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S

sof

x

y

z

Ueq

1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1

0.1285(5)0.1122(5)0.8650(5)0.8691(5)0.2616(13)0.2897(14)0.2264(13)0.9063(15)0.9294(13)0.3232(13)0.3338(13)0.0172(12)0.3779(13)0.5744(12)0.5632(12)0.3059(13)0.9519(12)0.2825(13)0.6496(13)0.6700(11)0.0295(12)0.0452(12)0.8857(13)0.7459(12)0.8607(13)0.7196(14)0.0215(12)0.6073(15)0.9960(14)0.9956(13)0.5802(13)0.5919(14)0.5831(12)0.9445(12)0.2680(14)0.3416(13)0.6987(13)0.3130(12)0.2873(14)0.6748(15)0.0633(5)0.4978(4)0.2701(5)0.7926(5)0.2461(12)0.0576(11)0.7643(11)0.2395(14)0.7702(11)0.8010(12)0.2299(11)0.3068(11)0.5085(12)0.7907(10)0.2056(12)0.4989(11)0.2925(12)0.0196(11)0.5569(11)0.9626(10)0.0429(10)0.4672(11)0.0056(11)0.7684(10)0.5213(11)0.2672(12)0.7221(11)0.7526(14)0.5306(12)0.9747(13)0.5612(10)0.2664(11)−0.0249(10)0.7099(11)0.4747(12)0.9926(12)0.0070(12)0.2370(11)0.7780(12)0.4971(12)0.74188(19)0.72710(18)0.85143(18)0.83906(19)−0.0179(5)0.1208(4)−0.0310(5)0.1091(6)0.1091(5)0.3529(5)0.3480(5)0.4456(4)0.5001(5)0.5951(5)0.5871(5)0.6621(5)0.6867(5)0.6668(5)0.7907(5)0.7878(4)0.8757(4)0.8768(5)0.5369(5)0.9235(4)0.5470(5)0.9296(5)0.4431(4)0.2300(6)0.2440(5)0.2440(5)0.0239(5)0.2365(5)0.0294(5)0.6813(4)0.1237(5)0.4884(5)0.3723(5)0.7967(4)0.8041(5)0.3627(6)0.0276(11)0.0184(10)0.0201(10)0.0256(11)0.027(3)0.024(3)0.020(3)0.037(3)0.021(3)0.021(3)0.024(3)0.018(2)0.021(3)0.015(2)0.024(3)0.022(3)0.023(3)0.021(3)0.027(3)0.017(2)0.014(2)0.020(3)0.024(3)0.013(2)0.020(3)0.022(3)0.016(2)0.038(3)0.030(3)0.028(3)0.023(3)0.024(3)0.018(2)0.018(2)0.028(3)0.023(3)0.020(3)0.017(2)0.025(3)0.034(3)detector, respectively, for baumhauerite and argentobaumhauerite. The SMART (Bruker AXS, 1998a)
system of programs was used for unit-cell determination and data collection, SAINT + (Bruker AXS,
1998b) for the reduction of the intensity data, and
XPREP (Bruker AXS, 1997) for space-group
determination and empirical absorption correction
based on pseudo ψ-scans. The centrosymmetricspace group P1 proposed by the XPREP program forargentobaumhauerite was chosen. It is consistent825

with the triclinic symmetry of the lattice andintensity statistics. The structure of argentobaumhauerite was solved by direct methods (Sheldrick,
1997a). The list of atom positions was completed insubsequent cycles of the refinement (Sheldrick,
1997b), by means of difference-Fourier syntheses. In
the final stage of refinement all the positions weretreated anisotropically. For baumhauerite the P1
space group was chosen. It is consistent with thetriclinic symmetry of the lattice and intensity

TABLE 4a. Selected cation-ligand distances (in Å) in argentobaumhauerite.
Pb8–
2.947(4) S28
2.967(3) S27
3.008(4) S23
3.078(3) S26
3.250(3) S33
3.259(3) S25
3.318(3) S31
3.319(3) S34
3.397(4) S29

Pb9–
Pb10–
2.973(3) S24 2.908(4) S30
2.817(4)2.992(3) S28 3.022(3) S33
2.876(4)3.026(3) S34 3.060(4) S35
2.968(4)3.159(4) S33 3.084(4) S34
2.985(4)3.198(4) S27 3.176(3) S36
2.995(4)3.217(3) S25 3.301(4) S35
3.147(3)3.245(4) S32 3.315(4) S32
3.376(4)3.283(3) S30 3.334(3)3.431(3) S26 3.401(3)826

Ag/Pb11
As1/Sb–
As2–
As3–
As4–
As5–
As6–
As7–
As8–
As9–
S7
2.599(4) S2
2.372(5) S1
2.241(4) S3
2.264(4) S7
2.245(4) S10 2.238(4) S11
2.267(4) S13
2.230(4) S15 2.273(4) S21
S6
2.694(4) S1
2.499(4) S5
2.293(4) S6
2.270(4) S9
2.252(4) S4
2.286(4) S17
2.325(4) S12
2.260(4) S17 2.293(4) S20
S5
2.713(4) S2
2.730(5) S3
2.494(4) S4
2.293(4) S8
2.307(4) S8
2.431(4) S18
2.620(4) S14
2.317(4) S18 2.298(4) S19
S2
2.892(4) S5
2.836(4) S2
2.835(4) S1
3.127(4) S4
3.275(4) S3
2.952(5) S14
2.653(4) S18
3.218(4) S22 3.109(4) S16
S1
2.973(5) S8
2.849(5) S4
3.536(4) S2
3.432(5) S3
3.358(5) S7
3.400(5) S13
3.079(4) S17
3.249(4) S21 3.225(4) S15
S1
3.237(4) S6
3.126(5) S4
3.563(4) S3
3.670(5) S2
3.527(5) S1
3.452(5) S15
3.569(4) S20
3.831(4) S23 3.517(4) S13
S3
3.483(4) S4
3.916(5) S2
3.728(4)S5
3.890(4) S6
3.723(4) S19
3.748(4)S9
3.892(4)
As10–
As11–
As12–
As13–
As14–
As15/Pb12–
As16–
As17–
S22 2.241(3) S24 2.219(4) S26 2.232(4) S27 2.232(4) S30 2.230(4) S36 2.546(4) S33
2.256(4) S34
2.258(4)
S16 2.278(4) S25 2.253(4) S19 2.271(4) S31 2.274(4) S28 2.253(4) S36 2.596(5) S32
2.258(4) S35
2.270(4)
S20 2.443(4) S23 2.326(4) S23 2.331(4) S29 2.380(4) S29 2.316(4) S35 2.596(4) S31
2.330(4) S32
2.645(4)
S15 3.131(4) S20 3.191(4) S20 3.094(4) S32 2.991(4) S32 3.201(4) S34 2.809(4) S35
3.142(4) S36
2.727(5)S14 3.259(4) S19 3.272(4) S24 3.444(4) S30 3.427(4) S31 3.228(4) S33 2.938(4) S36
3.349(4) S31
3.429(4)
S19 3.597(4)S21 3.642(3) S33 3.649(4) S36 3.863(5) S29 3.029(5)S36
3.747(4)
S28 3.856(4) S35 3.668(4)S18 3.859(4)2.269(4)2.278(4)2.341(4)3.016(4)3.217(4)3.434(4)DAN TOPA AND EMIL MAKOVICKY

Pb1–
Pb2–
Pb3–
Pb4–
Pb5–
Pb6–
Pb7–
S13 2.749(4) S14 2.778(4) S15 2.959(4) S16 2.895(4) S21 2.817(4) S25 2.951(4) S22
S9
3.007(4) S10 2.898(4) S18 2.980(4) S15 2.897(4) S16 2.823(3) S26 2.974(3) S21
S12 3.040(4) S9
3.070(4) S11 3.007(3) S14 3.170(3) S24 2.915(3) S29 3.044(4) S30
S10 3.090(4) S12 3.102(4) S12 3.192(4) S12 3.174(4) S18 3.029(3) S21 3.156(4) S25
S11 3.112(4) S11 3.159(3) S9
3.206(4) S9
3.178(4) S22 3.062(3) S27 3.213(3) S28
S63.202(4) S6
3.274(4) S7
3.213(4) S10 3.243(3) S17 3.188(4) S19 3.228(3) S24
S5
3.306(4) S4
3.417(4) S13 3.270(4) S11 3.245(3) S20 3.328(3) S22 3.269(3) S26
S7
3.562(4) S8
3.561(4) S16 3.417(3) S17 3.378(4)S28 3.303(3) S27
S3
3.998(5) S5
3.583(4) S10 3.667(4) S8
3.415(5)
S23 3.410(3) S20

ARGENTOBAUMHAUERITE

statistics. The structure of baumhauerite was solved
by direct methods (Sheldrick, 1997a). In the final
stage of refinement all positions were treatedanisotropically and the atomic sites were re-labelledin concordance with site denomination in baumhauerite made by Engel and Nowacki (1969).
Single crystal diffraction data indicate thatargentobaumhauerite is triclinic, a = 7.9053(10),b = 8.4680(10), c = 44.4102(53) Å, α = 84.614(2),β = 86.469(2), γ = 89.810(2)°, V(cell) = 2954.16 Å3,space group P1. In agreement with previous
investigations, the c parameter is doubled againstthat of baumhauerite. The substitution-free Moosegg
material is triclinic, a = 7.884(4), b = 8.345(4), c =22.811(11) Å, α = 90.069(8), β = 97.255(8), γ =90.082(8), V(cell) = 1488.8(13) Å3, space group P1.
Complete experimental and refinement data forboth minerals, argentobaumhauerite and baumhauerite, respectively, are given in Table 2. Atomic
position parameters, refined occupancies and Ueq
parameters are in Tables 3a and 3b, whereas tablesof complete anisotropic displacement parameters(Tables 3c and 3d) have been deposited with the
Principal Editor of Mineralogical Magazine and areavailable from ww.minersoc.org/pages/e_journals/
dep_mat_mm.html). The bond distances are given
in Tables 4a and 4b, and the polyhedron characteristics in Tables 5a and 5b.

Description of crystal structures
In agreement with its structure scheme, as asartorite homologue N1,2 = 3;4, the crystal structureof argentobaumhauerite contains 28 cation sites
and 36 sulfur sites. Only three cation sites, Ag–
Pb11, As1–Sb and As15–Pb12, were refined as
mixed sites. The lower symmetry of baumhauerite
leads to the same number of independent positions,from which Pb4–As17, As4–Pb14 and As5–Pb13
are mixed sites. Because of the very large numberof refined parameters, in both structures the same
positional parameters were used for both cations
which share a mixed site (Tables 3a,b). The detailsof the structures will be described according to thestructure segments defined for sartorite homologues by Makovicky (1985). These are slabs ofdifferent thickness, all based on the SnS archetype,
formed primarily by As coordination polyhedrawith a crankshaft arrangement of the short As–S
bonds, terminating in a zig-zag layer of Pb
coordination polyhedra.
Both crystal structures (Figs 1a,b) contain one
type of N = 3 slab built from arsenic coordination
827

polyhedra with participation of Pb (Figs. 2a,b). It
alternates regularly with N = 4 slabs. In the case ofargentobaumhauerite there are two kinds of N = 4
slabs in alternation; these display different degrees ofsubstitution of ‘fundamental’ cations, As and Pb, by
Ag (Fig. 2b). They will be called the ‘unsubstituted’and the ‘substituted’ kind of slab, respectively. In
baumhauerite there is only one compositional typeof N = 4 slabs. Both slab types are subdivided into
tightly-bonded double-layers, typical for the sartorite
homologues, which are formed by means of short
As–S bonds. The double-layers are separated bybroader spaces which accommodate the loneelectron pairs of (especially) As.
In argentobaumhauerite, the N = 3 slab iscomposed of six distinct columns of cations:Pb3–Pb4, Pb6–Pb7, Pb5–As8, As6–As7, As9–
As10 and As11–As12, with 8.5 Å periodicity. The
As7, 8, 9, 11, 12 atoms form trapezoidal coordination pyramids with three typical short bonddistances (Table 4a). They are alternatively
bottom- and side-bonded in their pyramidal bases(Fig. 3). The bottom-bonded As10 has one of these
distances extended to 2.44 Å; the extension isprobably forced by the configuration of surrounding Pb coordination polyhedra and LEP of arsenic.
The arsenic site As6 displays two short distances,
2.26 Å and 2.33 Å, whereas two more distances inthe base of the coordination pyramid are longer andequal (2.62 and 2.65 Å long); they oppose one
another. The As6 site is obviously a position
flipping between the bottom-bonded and sidebonded orientation, averaging the short and long
distances involved in the flip.
In the N = 3 slab, one side of the diagonallyorientated tightly-bonded double-layer is composed of well-developed crankshaft chains S24–
As11–S23–As12–S19–As9–S20–As10–S16; thethird short bond of each of these As atoms
bridges the double layer. Each crankshaft chain
ends in the Pb4 polyhedron, whereas the alternating
Pb3 polyhedron faces a gap between adjacentcrankshaft chains (Fig. 3). The opposite side of the
double layer has a very short chain S13–As7–S14–
As6–S17–As8–S18, complicated by the presenceof the flipping As6 position which alternates
between the short As6–S17 bond and the short
As6–S18 bond (Fig. 3); as already mentioned, bothof these distances show the bond length averaged to∼2.6 Å. Among the associated Pb atoms, Pb5 faces
a gap between adjacent crankshaft chains; becauseof this position, its polyhedron cross-section has awidely ‘open’ shape. In its 8.5 Å column, Pb5
alternates with As8. The Pb6 atom faces the As8

TABLE 4b. Selected cation–ligand distances (in Å) in baumhauerite.
Pb3–
Pb4–
Pb5–
Pb6–
Pb7–
Pb8–
Pb9–
Pb10–
2.727(12) S28 2.918(11) S25 2.601(12) S33 2.836(11) S11 2.832(12) S9
2.909(11) S12 2.976(10) S19 2.946(10) S12 2.805(10)2.926(10) S24 2.929(13) S5
2.681(10) S8
2.904(9) S9
2.964(11) S32 2.940(11) S14 2.987(10) S23 3.042(9) S34 2.819(10)3.090(9) S4
2.940(13) S31 2.711(11) S28 2.918(11) S36 3.180(13) S10 2.947(12) S19 3.026(10) S21 3.059(10) S15 2.932(10)3.109(10) S25 2.957(11) S26 2.947(11) S36 2.992(12) S33 3.188(11) S33 3.166(11) S8 3.026(9) S14 3.090(10) S11 2.995(12)3.172(10) S27 3.003(11) S24 3.272(12) S26 3.007(11) S21 3.220(10) S21 3.204(10) S21 3.191(10) S12 3.145(10) S14 3.120(10)3.367(11) S5
3.153(10) S2
3.388(10) S25 3.158(11) S8
3.230(10) S6
3.251(10) S13 3.191(12) S30 3.147(10) S16 3.214(9)3.513(11) S31 3.378(11) S6
3.713(12) S7
3.410(10) S19 3.239(10) S19 3.263(10) S11 3.239(10) S32 3.224(11) S13 3.323(10)3.573(11)
S32 3.244(11) S36 3.342(13) S9 3.336(11) S10 3.321(10)3.657(13)S7
3.374(11) S23 3.405(10) S32 3.422(11) S9
3.369(11)

828

Pb11–
Pb12–
As1–
As2–
As3–
As4–
As5–
As6–
As7–
As8–
S34 2.912(9) S27
2.913(11) S1
2.220(11) S27 2.186(11) S31 2.248(12) S26 2.492(11) S24 2.351(13) S33 2.217(11) S28 2.259(12) S32 2.225(11)S35 2.965(11) S22
2.987(11) S2
2.273(11) S3
2.223(11) S4
2.261(12) S5
2.535(11) S25 2.445(12) S7 2.325(11) S36 2.267(12) S6
2.270(12)S22 3.096(11) S20
3.010(9) S29 2.333(10) S29 2.331(10) S2
2.284(11) S4
2.755(13) S26 2.646(12) S6 2.383(12) S7
2.365(11) S23 2.308(10)S17 3.178(10) S15
3.027(12) S31 3.117(12) S31 3.200(12) S25 3.245(12) S24 2.869(13) S36 2.962(13) S28 2.930(11) S24 3.340(13) S7
3.182(11)S29 3.222(11) S35
3.197(11) S27 3.342(10) S2
3.236(11) S26 3.336(12) S29 3.114(11) S33 3.178(12) S24 3.108(14) S6
3.576(11) S8
3.379(10)S1
3.226(11) S3
3.286(11) S4
3.662(12)S28 3.565(12) S28 3.362(11) S23 3.405(10) S26 3.803(11) S25 3.739(11) S33 3.640(11)S16 3.229(10) S18
3.303(10) S22 3.963(13)S2
3.786(12) S6
3.767(11)
S31 3.976(12) S26 3.818(12)S20 3.232(9) S34
3.445(9)S33.316(11) S1
3.521(11)
As9–
As10–
As11–
As12–
As13–
AS14–
As15–
As16–
S8
2.204(10) S11
2.215(10) S21 2.218(12) S35 2.259(13) S14 2.251(12) S13 2.253(10) S18 2.200(10) S20 2.273(11)S92.263(11) S19
2.255(13) S30 2.257(10) S15 2.284(10) S34 2.305(10) S12 2.259(12) S22 2.238(13) S16 2.322(9)S23 2.315(10) S10
2.317(9) S10 2.340(9) S16 2.293(9) S13 2.598(11) S30 2.374(10) S17 2.326(10) S17 2.526(9)S73.135(11) S13
3.143(11) S13 3.056(10) S14 3.137(10) S35 2.970(11) S34 3.024(10) S15 3.155(10) S15 2.754(10)S6
3.196(11) S30
3.226(10) S11 3.384(11) S12 3.154(10) S17 3.249(11) S35 3.135(11) S16 3.236(9) S18 3.124(10)S143.964(12) S12 3.629(12) S10 3.556(13) S30 3.490(10) S18 3.530(12) S34 3.902(11) S35 3.491(12)S93.825(11)S16 3.977(10)S13 3.908(12) S30 3.784(11)S15 3.869(13)S3 3.830(11)DAN TOPA AND EMIL MAKOVICKY

Pb1–
Pb2–
S17 2.865(10) S18
S3
2.917(10) S3
S1
2.945(11) S20
S20 3.156(9) S22
S22 3.276(10) S1
S4
3.289(13) S27
S53.320(11) S5
S29 3.393(10) S31
S2
3.436(10) S4ARGENTOBAUMHAUERITETABLE 5a. Polyhedron characteristics for the refined structure of argentobaumhauerite.
Atom

1

2

3

4

5

6

7

8

Pb1
Pb2
Pb3
Pb4
Pb5
Pb6
Pb7
Pb8
Pb9
Pb10
Ag/Pb11
As1/Sb
As2
As3
As4
As5
As6
As7
As8
As9
As10
As11
As12
As13
As14
As15/Pb12
As16
As17

9
9
9
9
7
9
9
9
9
7
7
7
7
6
7
7
8
6
6
6
6
5
8
7
6
6
5
6

3.210
3.202
3.205
3.178
3.042
3.167
3.171
3.165
3.173
3.040
2.965
2.875
2.950
2.864
2.939
2.879
2.974
2.897
2.775
2.751
2.891
2.780
3.042
2.914
2.870
2.760
2.826
2.894

0.038
0.019
0.010
0.028
0.096
0.019
0.021
0.018
0.015
0.088
0.109
0.096
0.120
0.125
0.080
0.105
0.057
0.123
0.080
0.086
0.176
0.290
0.070
0.100
0.113
0.061
0.338
0.168

0.385
0.359
0.292
0.172
0.246
0.198
0.041
0.198
0.115
0.216
0.404
0.597
0.711
0.713
0.751
0.708
0.684
0.748
0.643
0.628
0.696
0.671
0.738
0.729
0.734
0.287
0.683
0.674

0.783
0.950
0.921
0.876
0.913
0.936
0.840
0.946
0.859
0.885
0.857
0.770
0.872
0.922
0.856
0.925
0.675
0.882
0.962
0.966
0.926
0.983
0.680
0.906
0.865
0.972
0.983
0.940

138.507137.572
137.938
134.497117.933
133.042133.551132.825133.800
117.711109.230
99.530107.545
98.391106.350
99.953110.138101.862
89.53887.176101.209
89.984117.868
103.652
99.06888.06794.586101.52365.20666.02766.85663.96840.33363.88663.98563.82864.46840.63736.82234.04635.79727.39037.04133.86245.02628.43626.21225.35426.55013.20647.51735.31227.96926.31812.93826.887

2.0
2.0
1.7
1.9
2.2
1.8
1.8
1.8
1.8
2.1
1.1
2.1
2.8
3.0
3.1
2.9
2.7
3.1
3.0
3.0
2.8
3.1
3.1
3.0
3.1
1.8
3.0
2.7

See foot of Table 5b for key.

polyhedron via a long S–S edge whereas Pb7 faces
Pb5 via a relatively short S–S edge (Fig. 3).
Across the thickness of the tightly-bonded
double layer, the crankshaft chains are faced by
Pb polyhedra, which participate in the compositionof the double layer and are situated on its opposite
surface. There are no short As–S bonds interconnecting the crankshaft chains on the two faces of thesame double layer, which also differ substantiallyand are orientated perpendicular to one another.
The slab of N = 3 double layers is not on elements ofsymmetry; it is asymmetric and the inversion centresof the P1 space group are situated in, and between,
double layers of the two kinds of N = 4 slabs.
The N = 3 slab in baumhauerite bears a close
resemblance to that in argentobaumhauerite(compare Fig. 4 and Fig. 3). The four-member
crankshaft chain S34–As13–S13–As14–S30–
As11–S10–As10–S11, with additional shortbonds As–S orientated to the opposite face of a829

double layer, corresponds fully to the four-member
chain in argentobaumhauerite. The short chain on
the opposing surface of the double-layer, S18–
As15–S17–As16–S16–As12–S15 with side bonds,
is analogous to the short chain in argentobaumhauerite but it is a typical crankshaft arrangement
because its As16 position lacks the flipping
character. Instead, As16 has a scheme 2.53 Å vs.
2.75 Å, and As16 has an elongate bond 2.53 Å inthe same position as in argentobaumhauerite.
The ‘unsubstituted’ N = 4 slab in argentobaumhauerite contains an inversion centre and consistsof the 8.5 Å columns of coordination polyhedra
As13–As14, As16–As17, Pb10–As15 and Pb8–
Pb9 (Fig. 5, right-hand side). The As13, As14,
As16 atoms have typical As coordinations(Table 4a). However, As17 has a 2.26 Å bond to
S34 in the vertex of the coordination pyramid,
2.27 Å to S35 in the base of the pyramid, and two
almost equal longer bonds in the pyramidal base,DAN TOPA AND EMIL MAKOVICKYTABLE 5b. Polyhedron characteristics for the refined structure of baumhauerite.
Atom

1

2

3

4

5

6

7

8

Pb1
Pb2
Pb3
Pb4
Pb5
Pb6
Pb7
Pb8
Pb9
Pb10
Pb11
Pb12
As1
As2
As3
As4
As5
As6
As7
As8
As9
As10
As11
As12
As13
As14
As15
As16

9
9
7
7
7
9
9
9
9
7
9
9
7
5
6
7
7
6
7
7
5
6
8
6
7
6
7
8

3.173
3.230
3.044
3.054
3.042
3.161
3.154
3.149
3.142
3.043
3.148
3.179
2.951
2.755
2.975
2.974
2.937
2.912
3.039
2.944
2.731
3.044
3.037
2.767
2.951
2.761
2.971
2.986

0.022
0.015
0.076
0.113
0.077
0.013
0.018
0.015
0.015
0.092
0.020
0.005
0.103
0.294
0.177
0.078
0.076
0.168
0.115
0.104
0.291
0.307
0.080
0.086
0.098
0.101
0.132
0.072

0.260
0.386
0.162
0.492
0.248
0.155
0.235
0.124
0.174
0.266
0.142
0.256
0.715
0.673
0.761
0.558
0.597
0.738
0.766
0.757
0.645
0.794
0.732
0.649
0.709
0.631
0.749
0.672

0.908
0.953
0.868
0.823
0.908
0.885
0.930
0.869
0.937
0.926
0.912
0.894
0.658
0.992
0.894
0.900
0.804
0.794
0.864
0.897
0.997
0.655
0.671
0.970
0.916
0.953
0.681
0.659

133.766
141.165118.096119.338
117.933132.293131.377130.782
129.934118.066130.702134.577
107.689
87.582110.290110.171
106.076103.451117.534
106.91285.337118.149
117.340
88.735
107.669
88.194109.879111.51064.03068.01441.30540.07941.18263.87363.15663.04662.63940.58762.65165.52336.55612.79328.88638.45537.08927.40939.34936.23612.51226.07246.81725.80336.74925.23236.09044.859

1.93
1.92
2.01
2.85
2.10
1.89
1.94
1.90
1.89
2.15
1.88
1.85
3.09
3.30
3.12
1.63
2.04
2.96
2.85
3.12
3.19
3.18
3.15
3.07
2.57
3.01
3.26
2.73

[1] Coordination number; [2] radius rs in Å of a circumscribed sphere, least-squares fitted to thecoordination polyhedron; [3] ‘volume-based’ distortion υ = [V(ideal polyhedron)–V(realpolyhedron)]/V(ideal polyhedron); the ideal polyhedron has the same number of ligands; [4]‘volume-based’ eccentricity ECCV = 1–[(rs–Δ)/rs]3 ; Δ is the distance between the centre of thesphere and the central atom in the polyhedron; [5] ‘volume–based’ sphericity SPHV = 1–3σrrs; σr isa standard deviation of the radius rs; [6] volume in Å3 of the circumscribed sphere; [7] volume in Å3of coordination polyhedron; [8] bond-valence sum.

2.64 Å and 2.73 Å, which indicate flipping inside
the coordination polyhedron. Flipping is apparently
connected with the statistical occupancy of theimmediately adjacent mixed site, modelled as 0.81
As15 and 0.19 Pb12, which has the shortest bonds
markedly longer than the As–S bonds, and equal to2.54 Å and 2 × 2.60 Å. The cigar-shaped anisotropic
displacement ellipsoid of this site is orientatedsymmetrically in the pyramidal base and describes
the mix of the more asymmetric As position with amore symmetrical Pb position. The As17 and As15
coordination polyhedra share a short 3.45 Å S–S
edge. The flipping As17 site is the end-site of acrankshaft chain S30–As14–S29–As13–S31–
830

As16–S32–As17–S35 (or –S36 as another shortbonded alternative) which eventually can continue
with the As15 position. The Pb10 polyhedron
alternating with the As15 site copies, to a modest
degree, the trapezoidal configuration of surrounding polyhedra but the polyhedra in the adjacent
Pb8–Pb9 column have fairly regular crosssections. The Pb8–Pb9 column completely backs
the just defined crankshaft chain, which is twocolumns broad, but situated on the opposite face ofthe double layer, as dictated by the inversion centre
in the double layer.
The ‘substituted’ N = 4 slab is centrosymmetricas well (Fig. 5, left-hand side). It is composed by

ARGENTOBAUMHAUERITE

FIG. 1. Atom labels for the crystal structure of (a) baumhauerite and (b) argentobaumhauerite.

columns As4–As5, As2–As3, ‘As1’–‘Ag’ andPb1–Pb2. In this slab, only the first, marginalcolumn is backed by Pb1 and Pb2 whereas the silvercontaining polyhedral columns back one another,
except for a side-shift of half-polyhedron width.
The composition of the crankshaft chain is
S7–As4–S8–As5–S4–As3–S3–As2–S1; the chain
continues to ‘As1’–S2 and ‘Ag’. In the perpendicular projection of the double layer, thecrankshaft chains on the opposite sides of the
double layer are antiparallel and continue one intoanother without a side-shift. Thus, the interspaces
between crankshaft chains in the interior of one
double layer, so-called secondary lone electronpair micelles (primary micelles are the large
interspaces between adjacent double layers), arecontinuous across the thickness of the double layer(Fig. 5), and participate in the accommodation oflone electron pairs. The corresponding situation in
the unsubstituted layer was much less definite
because of the heavy backing of crankshaft chains831

by Pb polyhedra. There are no short As–S bonds
interconnecting chains on the two faces of the‘substituted’ double layer (the bridging As1–S2
bond is 2.73 Å long) and only an elongate,
mixed-cation bond of this kind, As15–S36, isfound in the ‘unsubstituted’ double-layer.
The arsenic sites As2 to As5 in the substituted
layer have typical coordinations with three shortcation–sulfur distances (Table 4a) whereas the sites‘As1’ and ‘Ag’ are mixed sites for which theindividual occupancies had to be modelled, considering the refined electron count and satisfying a
stoichiometry of the mineral. The ‘As1’ site has
been refined as 0.74 As mixed with 0.26 Sb, withthe same set of positional coordinates and the sameanisotropic displacement parameters. The shortest
observed cation–anion distance is 2.37 Å to S2, and,
together with the next short distance 2.50 Å to S1(both situated in the base of the coordination
pyramid), it is in agreement with the cation
assignment. The two distances perpendicular to theDAN TOPA AND EMIL MAKOVICKY

FIG. 2. Comparison of fundamental elements of the crystal structures of (a) baumhauerite and (b) argentobaumhauerite.
The N = 3 and N = 4 slabs are divided into double-layer ribbons with tricapped trigonal coordination prisms of Pb attheir obtuse ends, and As- and LEP-based interior portions (coloured). The N = 3 slabs are dark grey in both structures,
whereas As-Pb saturated N = 4 layers are cyan in the argentobaumhauerite structure, and Ag-As rich N = 4 layers in thisstructure are light green. Baumhauerite has only one kind of N = 4 slab (Pb rich). Boxes indicate sites of crankshaft
chains defined in the text for each ribbon.

trapezoidal cross-section, 2.73 Å and 2.85 Å, to S2and S8, respectively, at the first sight do not agreewith such an assignment. However, the enormous
U33 value of the site (Table 3c,d deposited) probably
suggests that this site is split into alternative sub-sites(chiefly within the base of the pyramid and also to alesser degree along the S2–S8 line); these alternative
sub-sites might even be bound to the alternative
double layers. The nature of the major substituent,As, follows from the refinement but that of the minor‘Sb’ substituent is not directly confirmable.
The ‘Ag’ site was modelled and refined as
0.74 Ag and 0.26 Pb, with the set of distances,832

2.60 Å and longer (Table 4a), which simulate a
distorted, irregular tetrahedral bond set. The linear
coordination sometimes observed for Ag is absent(here 2.60 Å is opposed by 2.97 Å, to S7 and S1,
respectively, and 2.69 Å is opposed by 2.89 Å,
respectively to S6 and S2). The mixed Ag-Pb site
displays a good Ag bond valence (BV) value of 1.1,
supporting the assignment of silver. Its bonds/
distances show similarities to those of silver
sites, Me7, 17 and 26 in the crystal structure ofjasrouxite which contains a number of different
types of Ag coordinations (Makovicky and Topa,
2014). Correlation of partial occupancies in theARGENTOBAUMHAUERITE

FIG. 3. A slightly oblique view of the N = 3 double layers
in the crystal structure of argentobaumhauerite. Large
white spheres: S; intermediate grey spheres: Pb; small grey
spheres: As; black spheres: Ag; and dark sticks: short
As–S bonds.

FIG. 4. A slightly oblique view of the N = 3 double layer inthe crystal structure of baumhauerite. For conventions see
Fig. 3.

FIG. 5. A slightly oblique view of the N = 4 double layers in the crystal structure of argentobaumhauerite. From left toright: Configuration and As–S crankshaft chains in the substituted N = 4 slab, a nearly perpendicular view of the N = 3
slab, and the elements of the unsubstituted N = 4 slab. Large white spheres: S; intermediate grey spheres: Pb; small grey
spheres: As; black spheres: Ag; and dark sticks: short As–S bonds.

833

DAN TOPA AND EMIL MAKOVICKY‘Ag’ and ‘As1’ sites (Table 3a) is remarkable. The
actual Ag–As–Sb–Pb mixing scheme at these twosites can be more complex than the trend modelled
here.
The trigonal prismatic sites Pb1 and Pb2(coordination number (CN) = 9) show prominenteccentricity (Table 5a), which is much lower for the
rest of such Pb sites in the structure. Together withPb3, they show the largest radius of circumscribed
sphere and polyhedron volume. The As sites show
uniformly large eccentricity. Large sphericity
values, low distortion coefficient and uniform
eccentricity values indicate that a description of
As coordination polyhedra as CN = 6 and 7
polyhedra instead of CN = 3 polyhedra is a very
appropriate, natural approach: the LEPs present
about the same degree of steric activity for all As
sites.
The Pb3 site has the lowest bond valence value(1.7) – it might be a possible Tl site. The arsenicsites are tolerably close to BV of 3.0 (Table 5a),
except for the mixed sites As1 and As15, whichhave polyhedra larger than expected for pure As
and show lower BV values as a consequence of it.
Those arsenic sites which have coordinations
somewhat deviating from the ideal set of three,about equally short, distances, have bond valencevalues 2.8, and even 2.7 for more severe cases (As6and As17). The low BV values for sulfurs are allconcentrated around the ‘Ag’ and ‘As1’ sites withintense cation substitution and, as S36, next to thesubstituted site ‘As15’.
The N = 4 slab of baumhauerite displays configurations different from that of argentobaumhauerite.
It contains a four-member crankshaft chain S8–As9–As8–S6–As6–SS7–As7–S28 with the additional
short bonds orientated into the double layer. Its
continuation is stopped by the Pb3 position (Fig. 6).
On the opposing side of the double-layer, andperpendicular to the just described chain, a shortchain is developed, comprising S27–As2–S29–
As1–S2–As3–S31. All of these As atoms display
typical coordinations with three short As–S bonds ofabout equal length (Table 4b).
Sandwiched between the chain systems of the
N = 3 slab, and comprising the entire thicknessof the double layer, is a cluster of mixed sites,
designated as As4 (with 0.35 Pb), As5 (with
0.15 Pb) and Pb4(with 0.36 As) (Table 3b). The
cation–S distances are correspondingly modified(Table 4b) and anisotropic displacement ellipsoids
express the mixed character of the site. Except forthe (As,Pb)4 site, however, no signs of flipping
cation positions were seen.

FIG. 6. A slightly oblique view of the N = 4 double layer inthe crystal structure of baumhauerite. For conventions see
Fig. 3.

Comparison of argentobaumhauerite andbaumhauerite834

The unit cell of argentobaumhauerite is related tothat of baumhauerite as follows:a ¼ a, b ¼ b, c ¼ 2c  a þ b=2
A simpler choice of argentobaumhauerite crystal
axes, closer to the baumhauerite geometry, but lesssatisfactory from the formal point of view, is also
possible, as indicated already by Pring et al. (1990).
The consecutive asymmetric N = 3 double layers
are all orientated identically in baumhauerite (Fig. 4)
whereas they are orientated alternatively along + a and–a in argentobaumhauerite (Fig. 3), as dictated by the
inversion centres situated in the N = 4 slabs (Fig. 5).
The orientation of chains in N = 3 slabs in respect tothose in the ‘low-Pb’ face of the N = 4 double layers inbaumhauerite is the same as for the unsubstituted
slabs in argentobaumhauerite. The N = 4 low-Pb facein baumhauerite approximates in its occupancy,
although not in all configurations, the faces of the
double layers in the N = 4 unsubstituted slab of

ARGENTOBAUMHAUERITE

argentobaumhauerite. The argentobaumhauerite
cell ends up by 4.18 Å ‘higher’ along the 8.46 Å(=b) direction after the full 44.4 Å c period; thisdoes not happen in the baumhauerite after the22.8 Å c period. As already mentioned, theconfiguration of cation species is nearly the samein the N = 3 layers of baumhauerite (Fig. 4) as it is inargentobaumhauerite (Fig. 3). In both structures, thetwo kinds of chains on the opposing faces of
the N = 3 double-layer are perpendicular to one
another.
Investigating the width of blocks in the two
structures, we measured the suitable cation–cationand S–S distances across the individual blocks,
preserving the ‘height’ of atoms we use in relation
to the 8.5 Å direction. The width of the N = 3 slab,
expressed as the S11–S23 distance in argentobaumhauerite, is 10.89 Å, whereas when it isexpressed as the As11–Pb4 distance, it is 7.61 Å.
The corresponding distances in baumhauerite are
S10–S20, which makes 11.14 Å (As10–Pb11 equal
to 7.75 Å). The N = 4 slabs have widths S28–S29
equal to 14.59 Å (As14–Pb8 equal to 11.49 Å) in
the unsubstituted slab of argentobaumhauerite, andS8–S9 equal to 14.36 Å (As4–Pb2 equal to11.36 Å) in the substituted slab. In baumhauerite,these distances are S3–S23 equal to 15.27 Å (As6–Pb2 equal to 12.30 Å). As for the unit-cell volume,that of argentobaumhauerite is 2954.2 Å3 whereas
two times the unit-cell volume of baumhauerite is2977.6 Å3.
Thus, the baumhauerite structure is expanded
when compared to argentobaumhauerite, even in
the portions not directly involved in the Ag + As –for – 2Pb substitution. One consequence of relative
compression is the appearance of flipping As
positions in the structure of argentobaumhauerite,
which are absent in the more expanded versions of
the slab motif in baumhauerite.
The tightly-bonded double layer in dufrénoysite,
N = 4, (Marumo and Nowacki 1967) is asymmetric,
with crankshaft chains on the opposite faces
perpendicular to one another. One side has a fourmember chain, the other face has a three-member
chain. A grouping of two (Pb,As) sites in the central
part of the slab is similar but not identical to that in
the N = 4 slab of baumhauerite.
The tightly bonded double layer in rathite N = 4(Marumo and Nowacki 1965) has four-member
chains, followed by an Ag position; Ag alternates in
its column with Pb6; the last column are the trigonal
prismatic sites Pb1–Pb2. Interestingly, the ultimate
As position at the inner end of the chain has anelongated As–S bond of 2.68 Å, opposed by adistance of 2.71 Å, similar to the situation observedin argentobaumhauerite.
Concerning the chain orientations, Makovicky(1985) and Berlepsch et al. (2001) have noted
previously that the orientation of crankshaft chainson the opposing sides of tightly-bonded double
layers differs between the unsubstituted members (N˃ 3) and the corresponding Ag-substituted ones; atthat time the latter category only contained rathite.
The chains were usually shorter and perpendicular to
one another in the former category and longer andparallel with one another, in the latter category. In
baumhauerite, the chains on opposing sides of adouble layer, both for the N = 3 and N = 4 slabs, runperpendicular to one another, although they are not
identical because of the lacking intraslab symmetry(Figs 4, 6). In argentobaumhauerite, the perpendicular orientation of chains is preserved in the N = 3
slabs but in both types of N = 4 slabs the crankshaft
chains on the two surfaces of the double layer are(anti)parallel, related by an inversion centre in the
double layer. In addition, in the adjacent, nonequivalent (i.e. the substituted vs. the unsubstituted)
N = 4 slabs, they slope in the opposing directions(Fig. 5), producing the effect observed by Pring andGraeser (1994) in HRTEM images and described bythem as a ‘reversal of the baumhauerite cell’ (see theIntroduction section). Thus, the baumhauerite–
argentobaumhauerite pair parallels the dufrénoysite–rathite pair in the configuration of the arsenic-based
chains and of entire slabs.
Position of baumhauerite varieties inrespective mineralizations

835

Among the examined set of samples enumerated
above, we found 36 samples contained argentobaumhauerite and argentobaumhauerite associations
with other sartorite homologues. Eight of them werepure baumhauerite–argentobaumhauerite aggregates.
They displayed prominent, fine to medium-coarse
lamellar and spindle-like exsolutions of argentobaumhauerite from baumhauerite (Fig. 7b). Twosystems of exsolution lamellae at oblique angles to
one another are common. In BSE photographs, theargentobaumhauerite lamellae are distinctly darker
than baumhauerite. Based on optical behaviour, thedetails of lamella orientation might differ from thematrix although the exsolution lamellae show astructurally determined shape. The single caserepresenting exsolution of baumhauerite fromargentobaumhauerite, in the form of thin spindles,
thick irregular spindles, accumulations along grainboundaries, as well as half-spindles andDAN TOPA AND EMIL MAKOVICKY

FIG. 7. BSE and reflected light (crossed polars) figures of baumhauerite and argentobaumhauerite aggregates from
Lengenbach, Binntal, Switzerland. Abbreviations: bmh – bauhauerite; agbmh – argentobaumhauerite; rth – rathite;
srt – sartorite. Exsolutions and replacements illustrated in figures a–d are described in the text.

embayments reaching from the boundaries into thegrains, is illustrated in Fig. 7a.
We ascribe genesis of the argentobaumhauerite
aggregates in the form of lamellae and spindles
inside the baumhauerite matrix to exsolution
processes, and with them connected migration of
Ag to the grain boundaries of baumhauerite, with
836

subsequent replacement of marginal grain portions
by argentobaumhauerite. Argentobaumhauerite
has been replaced to a different degree by
rathite and sartorite (Fig. 7c). Both replacement
processes show dependence on the crystallographic
orientation of the original argentobaumhauerite.
Sartorite replaces rathite as well, without regard

ARGENTOBAUMHAUERITE

FIG. 8. Composition triangle (Pb + Hg) – (As + Sb) – (Ag + Cu + Tl) (atomic proportions of cations) with (a) known
minerals of the sartorite homologous series and (b) baumhauerite, argentobaumhauerite and associated sartorite
homologues from Lengenbach, analysed in the present work. References: [1] Berlepsch et al. (2003); [2] Makovicky
et al. (2012); [3] Makovicky and Topa (2012); [4] Topa (unpublished data); [5] Laroussi et al. (1989); [6] Orlandi et al.
(2012); [7] Moëlo et al. (2008); [8] Berlepsch et al. (2002); [9] Topa et al. (2013); and [10] Biagioni et al. (2014).
Numbers 1 and 2 in (a) and (b) indicate 1Ag and 2Ag per formula unit. (i.e. AgPb22As33S72 and Ag2Pb20As34S72,
respectively). Note: sartorite and dufrénoysite are Ag-, Cu-free, Tl-based phases.

to its orientation (Fig. 7d ). As a result of the seriesof exsolutions and replacements, pure mineral
grains of sartorite homologues are rare at
Lengenbach.
The position of the analysed sartorite homologues from Lengenbach in the Pb – (Ag + Cu + Tl) –(As + Sb) system is illustrated in Fig. 8a and b.
Baumhauerite and argentobaumhauerite occupy
the central line of the diagram as two well-separated
composition clusters. The As–Sb diagram (Fig. 9a)
indicates that the As–Sb ratios in baumhauerite and837

argentobaumhauerite are a part of a single baumhauerite – rathite – sartorite sequence in which,very broadly, the Sb content is a function of the As
content: at.% Sb ≈0.133 at.% As. Dufrenoysite lies
outside this trend. The Tl–Ag diagram (Fig. 9b)
sharply separates the Ag-substitution and the Tlsubstitution lines of these sulfosalts. Dufrenoysite
matches the low Ag contents observed in baumhauerite from Lengenbach whereas the linear
increase of Tl contents from baumhauerite
through argentobaumhauerite to rathite does not

DAN TOPA AND EMIL MAKOVICKY

FIG. 9. (a) As–Sb and (b) Tl–Ag correlations for the sartorite homologues from Lengenbach, present in the baumhauerite
samples and analysed in this study. Element concentrations are expressed in atomic percent.

reach even a quarter of the trend observed fromsartorite to dufrenoysite. This might indicate thatthe rathite stage is a continuation of the baumhauerite stage whereas the subsequent sartorite deposition, confirmed by the textural observations
described above, and the replacement processes
were produced by solutions with a different
composition. The position of dufrénoysite is still
open. We find it interesting, that philrothite, ideallya nearly pure Tl–As–S phase (Bindi et al., 2014)
appears to be a product of a late mineralization
phase.
Baumhauerite and argentobaumhauerite are justa part of the deposition sequence of Pb–As
sulfosalts at Lengenbach and the above described
observations help to fix their position in thissequence. If confirmed by further observations,the separation of Ag enriched and Tl enriched
mineralization periods in the deposit is remarkable.
The substitution-free baumahuerite material
comes from Moosegg near Grubach, ∼4 km from
Golling, Salzburg Land, Austria (Graeser et al.,1986). The sulfide mineralization occurs in association with a gypsum-anhydrite mass which contains
inclusions of Werfen slates and altered volcanic
rocks, and with marls, limestones and dolomites ofGutenstein formation. A locally developed, thinsulfide horizon contains a baumhauerite-sphalerite
mineralization with minor liveingite(?) and/or
dufrénoysite(?), enargite, galena, sulfur, pyrite andseligmannite. In the same locality, a galenasphalerite mineralization also occurs, with pyrite
and jordanite. Mineralization is believed to havebeen formed by the elements concentrated fromsurrounding sediments.

Conclusions

838

Argentobaumhauerite is a homeotype of baumhauerite. The difference is expressed as a different(‘Ag substituted’) composition, a supercell of thebaumhauerite cell, and a different arrangement ofshort As–S bond configurations (crankshaft
chains) in the structures. The remarkable unitcell scale separation of Ag and surplus As into analternative set of N = 4 slabs, creating well
localized (Ag + As,Sb) substitution sites, is
responsible for the doubling of the c parameter.
It raises a question whether there exists a purephase with only silver-substituted N = 4 slabs.
Structurally, it might face a size misfit between the
N = 3 and N = 4 slabs, which is adjusted easily
when every second N = 4 slab is Pb rich. The
perfection of intra-cell separation of the unsubstituted and extensively substituted portions isquite surprising although the HRTEM observations of Pring et al. (1990) reveal that it could also
be arrested at different stages of the process.
Argentobaumhauerite is not a polytype ofbaumhauerite – it is an independent mineral
species with its own local (crankshaft chain)configurations and local symmetries (inversion
centres instead of complete asymmetry), bothvery different from baumhauerite, and with cation
substitution sites which are not present in baumhauerite. Thus, it is not just presence or absence of
inversion relating adjacent structural slabs, but theslabs themselves in the two mineral species are
configured differently. It was rather unfortunate
that, due to the history of its research, its former
name (i.e. baumhauerite-2a) resembled a polytype.

ARGENTOBAUMHAUERITEThe HRTEM observations inevitably do not reachthe degree of resolution detail which would
illustrate the here described crankshaft chain
schemes and substitutions. Thus, the models ofPring and Graeser (1994) were just the first
approximation to the true structural situation.
Acknowledgements
The authors express their gratitude to all the above listed
donors and institutions which contributed material tothis study. The paper was handled by Sergey
Krivovichev and the comments of Allan Pring and an
anonymous reviewer helped to improve the paper.

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