Mineralogical Magazine (2019), 83, 733–739
doi:10.1180/mgm.2019.45

ArticleHitachiite, Pb5Bi2Te2S6, a new mineral from the Hitachi mine,
Ibaraki Prefecture, Japan
Takahiro Kuribayashi1*, Toshiro Nagase2, Tatsuo Nozaki3,4,5,6, Junichiro Ishibashi7, Kazuhiko Shimada7,

Masaaki Shimizu8 and Koichi Momma91

Department of Earth Science, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan; 2The Tohoku University Museum, Tohoku University, Sendai
980-8578, Japan; 3Research and Development Centre for Submarine Resources, Japan Agency for Marine-Earth Science and Technology, Yokosuka, 237-0061, Japan;
4
Frontier Research Centre for Energy and Resources, School of Engineering, The University of Tokyo, Tokyo 113-8656, Japan; 5Department of Planetology, Kobe
University, Kobe 657-8501, Japan; 6Ocean Resources Research Centre for Next Generation, Chiba Institute of Technology, Narashino 275-0016, Japan; 7Departmentof Earth and Planetary Sciences, Faculty of Science, Kyushu University, Fukuoka 819-0395, Japan; 8Department of Earth System Science, Graduate School of Scienceand Engineering for Education, University of Toyama, Toyama 930-8555, Japan; and 9Department of Geology and Paleontology, National Museum of Nature andScience, Tsukuba 305-0005, Japan.

Abstract
Hitachiite, Pb5Bi2Te2S6, is a new mineral discovered in the Hitachi mine, located in the Ibaraki Prefecture of Japan. The mean of 21
electron microprobe analyses gave: Pb 52.01, Bi 23.06, Fe 0.69, Sb 0.17, Te 13.74, S 9.71, Se 0.54, total 100.04 wt.%. The empirical chemical formula based on 15 apfu is (Pb4.75Fe0.23)Σ4.98(Bi2.09Sb0.03)Σ2.12Te2.04(S5.73Se0.13)Σ5.86, ideally Pb5Bi2Te2S6. Synchrotron single-crystal
X-ray diffraction experiments indicated that hitachiite has trigonal symmetry, space group P3m1, with a = 4.2200(13) Å, c = 27.02(4) Åand Z = 1. The four strongest diffraction peaks shown in the powder X-ray pattern [d, Å (I)(hkl)] are: 3.541(35)(012), 3.391(59)(013),
3.039(100)(015) and 2.114(56)(110). The calculated density (Dcalc) for the empirical chemical formula is 7.54 g/cm3.
The crystal structure of hitachiite has been refined using synchrotron single-crystal X-ray diffraction data, to R = 7.38% and is basedon ABC-type stacking of 15 layers (five Pb, two Bi, two Te, and six S layers) along the [001] direction, and with each layer ideallycontaining only one kind of atom. The stacking sequence is described as Te–Bi–S–Pb–S–Pb–S–Pb–S–Pb–S–Pb–S–Bi–Te. The discoveryof hitachiite implies that the minerals of the Bi2Te2S–PbS join might form a homologous series of Bi2Te2S·nPbS.
Keywords: hitachiite, new mineral, tetradymite group minerals, homologous series(Received 28 February 2019; accepted 6 July 2019; Accepted Manuscript published online: 15 July 2019; Associate Editor: František Laufek)

Introduction
Hitachiite, Pb5Bi2Te2S6, is a new mineral discovered in the Hitachimine, Ibaraki Prefecture, Japan. The chemical formula of hitachiite
is plotted on the join of Bi2Te2S (tetradymite)–PbS (galena) in thesystem Bi–Pb–(Te, S). The join also includes aleksite (PbBi2Te2S2)
and saddlebackite (Pb2Bi2Te2S3), which belong to the tetradymitegroup of minerals in the 9th edition of the Strunz mineral classification system (Strunz and Nickel, 2001). The mineral and its
name have been approved by the Commission on New
Minerals, Nomenclature and Classification of the International
Mineralogical Association (IMA2018-027, Kuribayashi et al.,2018). The type specimen of hitachiite is deposited under catalogue
number NSM-M45821 in the National Museum of Nature andScience, Tsukuba, Ibaraki Prefecture, Japan.
The crystal structures of the tetradymite group of minerals canbe considered as combinations of several structural units. Bindi andCipriani (2003) investigated Pb-enriched baksanite (Bi5Pb)Te2S3;*Author for correspondence: T. Kuribayashi, Email: takahiro.kuribayashi.a7@tohoku.ac.jp
Cite this article: Kuribayashi T., Nagase T., Nozaki T., Ishibashi J., Shimada K., Shimizu
M. and Momma K. (2019) Hitachiite, Pb5Bi2Te2S6, a new mineral from the Hitachi mine,
Ibaraki Prefecture, Japan. Mineralogical Magazine 83, 733–739. https://doi.org/10.1180/
mgm.2019.45

baksanite, Bi6Te2S3, is one of the tetradymite group of minerals),
and reported that its crystal structure can be described as an alternation of modules of an ingodite-type structure (Bi2TeS) and of ajoséite-A-type structure (Bi4TeS2). Similarly, hitachiite can beconsidered as a homologous series of PbnBi4Te4Sn+2 in the Pb–Bi
tellurosulfides proposed by Cook et al. (2007a,b). The general formula has been reviewed by Moëlo et al. (2008) as Pb(n–1)Bi2Ch(n+2)(Ch = Te, Se and S) on the basis of the tetradymite archetype. It istherefore important to determine the crystal structure of hitachiite
in order to classify it in the tetradymite group of minerals. The
discovery of hitachiite presents the possibility of forming ahomologous series with aleksite and saddlebackite, expressed as
Bi2Te2S·nPbS. As the crystal structures of aleksite and saddlebackite have not been determined so far, determining the structure ofhitachiite could help in understanding the structural and crystal
chemistry of minerals in the system Bi2Te2S–PbS. In this report,
we present the structure of hitachiite refined using single-crystal
synchrotron X-ray diffraction data.
Occurrence and appearance
Hitachiite was discovered at the Hitachi mine, located in the city of
Hitachi, Ibaraki Prefecture, Japan (36°37’16.03′′ N, 140°36′ 46.50′′ E).
The Hitachi mine comprises Fudotaki and Fujimi deposit groups,© Mineralogical Society of Great Britain and Ireland 2019

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Table 1. Reflectance data (R1 and R2 in %) in air and oil of hitachiite.
Air

Oil

λ (nm)

R1

R2

R1

R2

400
420
440
460
470
480
500
520
540
546
560
580
589
600
620
640
650
660
680
700

38.4
40.0
41.6
41.7
41.8
41.9
41.8
41.7
41.6
41.5
41.4
41.2
41.1
41.1
40.8
40.8
40.7
40.7
40.6
40.3

35.8
36.3
37.4
38.3
38.5
38.7
39.0
38.9
38.9
38.8
38.7
38.6
38.4
38.1
38.1
38.1
38.1
38.0
37.8
37.5

30.3
30.4
30.4
30.3
30.2
30.0
29.7
29.3
29.3
29.0
28.8
28.7
28.4
28.4
28.3
28.3
28.3
28.2
28.1
27.9

25.1
25.9
26.8
27.4
27.7
27.8
28.0
28.1
28.1
28.0
27.9
27.9
28.2
28.2
28.2
28.2
28.3
28.4
28.4
28.4

The values required by the Commission on Ore Mineralogy are given in bold.

lustre and black streak. The macroscopic colour of hitachiite issilver grey. Polished specimens of hitachiite reveal that its bireflectance is weak with no observable pleochroism; its anisotropy is
weak and no internal reflections are shown. Hitachiite has a
Mohs’ hardness of 2½–3. Its calculated density is 7.54 g/cm3
when using the empirical chemical formula and structural data
(Z = 1).
Fig. 1. Optical reflected light microscopy images of hitachiite: (a) magnified image ofa hitachiite grain; and (b) hitachiite found commonly in pyrite. Holotype specimen,
catalogue number NSM-M45821.

with the aforementioned Fudotaki deposit being one of the representative orebodies of the Fudotaki group (Kase and Yamamoto, 1985).
The Fudotaki deposit is classified as a volcanogenic massive sulfide(VMS) deposit and a Cu–Zn sulfide deposit with small amounts of
Pb. The Fudotaki sulfide ores have been metamorphosed into lower
epidote–amphibole facies via regional metamorphism. The primary
formation age of the Fudotaki deposit was estimated to have been
formed during the Cambrian period. The Fudotaki deposit is recognised as the oldest dated ore deposit in Japan by both zircon U–Pb
radiometric determinations and Re–Os isotope isochron methods(Tagiri et al., 2011; Nozaki et al. 2014).
Emeritus Prof. K. Kase of Okayama University collected samples (including hitachiite) from the Fudotaki deposit at Hitachi
mine to investigate geochemically its mineralisation and metallogenesis (Kase, 1978; Kase and Yamamoto, 1985). Hitachiite crystals occur as tiny grains within pyrite crystals (Fig. 1a,b) and arecommonly found with pyrite, chalcopyrite, minor amounts ofsphalerite and pyrrhotite and very minor amounts of galena
and marcasite. The individual grains are ∼10–100 µm in size.

Optical and physical properties
The polished section including abundant hitachiite crystals weremade using the type specimen with catalogue number
NSM-M45821. Hitachiite is an opaque mineral with a metallic

Reflectance data
After optical observations, reflectance measurements were conducted on selected hitachiite crystals within the polished section.
Reflectance measurements for hitachiite were performed against a
WC009 standard material, which had been measured relative to a
WTiC (Zeiss 314) by the late A.J. Criddle. Immersion measurements were performed using Nikon oil (ND = 1.515) at room temperature (20°C). A Nikon Optiphot-2 microscope photometerwith a Nikon photometer-head-measurement-finder, a Nikon
photometer controller P101, a Nikon monochromator G-70 anda Nikon two-light-flux interference examination installed at the
University of Toyama were used for these measurements. The
reflectance data are summarised in Table 1
Chemical data
The composition of hitachiite was obtained using a field emission
electron probe micro-analyser (JEOL, JXA-8530F) at Kyushu
University, under operating conditions of 20 kV and 10 nA with abeam diameter of 0.1 µm. Counting time was set at 40 s for eachelement. Standard materials used to quantitatively analyse thesamples were: galena for Pb; bismuthinite for Bi; Sb2Te3 for Te; pyrite for Fe and S; stibnite for Sb; and In2Se3 for Se. The measured
X-ray intensities were corrected using the ZAF method. Although
the compositions of some samples are slightly different, no chemical zoning was observed in hitachiite grains (Fig. 2). One-point
analysis was conducted per hitachiite crystal within the polishedsection used for optical observation and reflectance measurement,

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Fig. 2. Back-scattered electron image of a hitachiite grain. Holotype specimen, catalogue number NSM-M45821.

and the results of 21 analyses are summarised in Supplementary
Table S1 (see below); these results yield hitachiite’s empirical formula of (Pb4.75Fe0.23)Σ4.98(Bi2.09Sb0.03)Σ2.12Te2.04(S5.73Se0.13)Σ5.86
based on 15 atoms per formula unit. The ideal chemical formulafor hitachiite is Pb5Bi2Te2S6. The chemical formula of hitachiitelies on the join of Bi2Te2S–PbS (Fig. 3a).
Crystallography
The powder X-ray diffraction (PXRD) pattern of hitachiite wasobtained using a Gandolfi camera with a diameter of 114.6 mm
and Ni-filtered CuKα radiation (λ = 1.54187 Å) installed at the
National Museum of Nature and Science. The data were recordedon an imaging plate and processed through a Fuji BAS-2500 bioimage analyser using computer software written by Nakamuta(1999). The sample used for the PXRD experiment was thesame as that used for single-crystal XRD experiment. The
PXRD profile of hitachiite and its peak information are shown735

in Supplementary Fig. S1 and Table 2, respectively. The fourstrongest diffraction peaks shown in the powder X-ray pattern[d, in Å, (Irel.), (hkl)] are: 3.541 (35) (012), 3.391 (59) (013),
3.039 (100) (015) and 2.114 (56) (110). The diffraction positions
were calibrated using silicon as an internal standard. The reflections
were indexed by reference to simulated patterns based on therefined crystal structure. The lattice parameters obtained fromPXRD are a = 4.2292(12) Å, c = 27.069(8) Å and V = 419.3(3) Å3.
Single-crystal XRD experiments were conducted using an
automated four-circle X-ray diffractometer with synchrotron radiation at the beam line BL-10A, Photon Factory, High Energy
Accelerator Research Organisation, KEK, Japan. The wavelength(λ = 0.70134 Å) of synchrotron radiation was calibrated using
the obtained unit-cell volume of the ruby standard material(NIST-SRM-1990). In the X-ray oscillation photographs, mostof the samples showed diffused and/or streak reflections due toits structural stacking sequence, therefore, a fragment of hitachiite
was selected carefully to determine the crystal structure (Fig. 4).
The dimension of the sample is ∼0.05 mm × 0.02 mm × 0.02 mm,with a chemical formula of (Pb4.60Fe0.25)Σ4.85(Bi2.24Sb0.02)Σ2.26Te2.15(S5.62Se0.13)Σ5.75 (No. 5-2 in Table S1). The lattice parameters were
determined as follows: a = 4.2200(13) Å, c = 27.02(4) Å and V =416.7(7) Å3, based on the 80 centred reflections in the 2θ range
19.1–36.4°. These values are in good agreement with those obtained
by PXRD. The X-ray diffraction intensity data were collected up to
2θmax = 60° using a scintillation type detector. Double the uniquereciprocal region was measured to check the Laue group. The intensity distribution indicates characteristics of the Laue group 3m1. The
absorption coefficient (μ) of the hitachiite sample is 71.7 mm–1.
Refdelf type absorption correction (XABS2; Parkin et al., 1995)
was applied to our dataset using the WinGX software (Farrugia,
1999). The value of Rint was decreased from 10.8% to 8.6% after
the correction. As no systematic absences were observed in themeasured intensities, the space group of hitachiite was expected
to be P3m1, P3m1 or P321. The crystal structure of hitachiite
was solved against these space groups via the charge-flipping
method (Oszlanyi and Suto, 2004) using the SUPERFLIP software(Palatinus and Chapuis, 2007). As a result, the P3m1 structuralFig. 3. Chemical properties of hitachiite and related minerals: (a) the minerals on the tetradymite–galena join in the system Pb–Bi–(Te + S); and (b) the compositional variation of hitachiite (shown by the blue area).

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Table 2. Powder X-ray data with normalised (d in Å) and calculated intensity ofhitachiite.
Iobs

3
4
35
59
4
100
6
2
3
3
14
56

11

13*
2

9
18
18

7

Icalc
0.2
0.1
0.5
0.8
1.3
1.8
3.0
0.3
2.9
22.5
38.3, 16.2
6.2
100.0
0.2
10.4
0.4
1.3
2.0
0.4
3.6
0.3
17.6
42.7
0.0
0.0
0.3
0.0
16.1
0.2
0.5
0.3
1.1
1.1
2.3
0.0
0.4
3.3, 7.0
0.6
6.0, 15.1
1.0
17.4
0.3
1.3
1.9, 5.3
0.5
0.3
0.4
0.5
0.6
0.1
0.9

dobs (Å)

3.872
3.635
3.541
3.391
3.222
3.039
2.839
2.658
2.483
2.323
2.177
2.114

2.040

1.920
1.856

1.812
1.793
1.735

1.692

dcalc (Å)

hkl

27.03113.515
9.010
6.758
5.406
4.505
3.862
3.655
3.623
3.529
3.387, 3.379
3.215
3.028
3.003
2.839
2.703
2.655
2.481
2.457
2.321
2.253
2.173
2.111
2.104
2.085
2.079
2.055
2.039
2.015
1.966
1.931
1.918
1.911
1.852
1.828
1.824
1.811, 1.807
1.802
1.791, 1.79
1.764
1.731
1.727
1.707
1.694, 1.689
1.664
1.652
1.616
1.608
1.601
1.590
1.561

001
002
003
004
005
006
007
010
011
012
0 1 3, 0 0 8
014
015
009
016
0 0 10017
018
0 0 11019
0 0 120 1 10110
111
112
0 0 13113
0 1 11114
115
0 0 140 1 12
116
117
020
021
0 2 2, 0 1 13
0 0 150 2 3, 1 1 8
024
025
119
0 1 140 2 6, 0 0 16
1 1 10027
0 1 15028
1 1 110 0 17029*This diffraction peak was overlapped with peaks of pyrite. Theoretical powder data arecalculated on the basis of the structural model refined by single-crystal X-ray diffraction
analysis using a four-circle diffractometer.

model was shown to be eventually most suitable. The atom positions were obtained by inspecting the electron density distributions, and three Pb, one Bi, one Te and three S sites being
assigned. The site for the Bi atom was assigned to form a Te–
Bi–S stacking sequence, with reference to the possible sequenceof several synthesised phases as proposed by Liu and Chang(1994) and Cook et al. (2007a,b). The neutral X-ray scattering factors taken from the International Tables for Crystallography
Volume C (Prince, 2004) were applied in the structure refinement.
As distinguishing between Pb and Bi is difficult owing to theirsimilar scattering factors, the metal sites were considered to be

Fig. 4. X-ray oscillation photo of hitachiite taken using synchrotron X-ray radiation
with imaging plate. The oscillation angle is ∼10°.

occupied by one kind of atom (Pb or Bi). Based on the chemical
formula of the examined sample, we considered that a small
amount of Fe, Sb and Se were accommodated at Pb, Bi and S
sites, respectively. Excess contents of Bi and Te were also divided
into Pb and S sites, respectively. Anisotropic displacement factors
were applied to Pb and Bi sites, whereas isotropic displacement
factors were applied to Te and S sites. An additional site in theinterlayer of Te–Te was found after performing a
difference-Fourier calculation of the examined sample; this additional site was designated as the TeB site. TeA and TeB sites
were too close to be occupied simultaneously. Constraints forthe site occupancy and the isotropic displacement factor wereapplied to these sites as follows: (1) the summation of the occupancy of TeA and TeB is equal to 1; (2) UTeA is equal to UTeB.
As this TeB site and another set of residual peaks could be causedby poor crystal quality, such as stacking faults due to chemicalvariation, we considered that the ideal structure of hitachiite
may not possess this site. The residual R value was converged
to 9.76% (no absorption correction). After the XABS2 absorption
correction, it was improved to 7.38%. All calculations of our structural refinements were performed using SHELXL97 (Sheldrick
and Schneider, 1997) with WinGX crystallographic software(Farrugia, 1999). The calculated powder X-ray intensities
obtained from this structural model are in good agreement withthe measured data (Table 2). Miscellaneous information on datacollections are summarised in Table 3 and the final atomic coordinates and anisotropic displacement factors are listed in Table 4.
Information on selected interatomic distances in the hitachiite
structure are summarised in Table 5. Drawings of each structure
were produced using VESTA 3 (Momma and Izumi, 2011). The
crystallographic information files have been deposited with the
Principal Editor of Mineralogical Magazine and are available
with the Supplementary material.
Crystal structure and its relation to other known phases
The ideal composition of hitachiite is Pb5Bi2Te2S6 and it could be
regarded as (Pb5Bi2)Σ7(Te2S6)Σ8, which corresponds to the tetradymite group (2.DC.05) in the 9th edition of the Strunz mineral

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Table 3. Detailed information on data collection and structural refinement.

Table 5. Selected bond distances (Å) in hitachiite with several reference data.

Crystal data
Ideal formula
Crystal dimensions (mm)Crystal system, space group
Unit-cell dimensions (Å)
Unit-cell volume (Å3)
Z
Dcalc (g·cm–1)
Temperature (K)Absorption coefficient (mm–1)
Data collection
Radiation type, wavelength (Å)
2θmax (°)
Absorption correction
Reflections measured, independentand observed reflections (I > 2σ(I))
Structure solution
Refinement
Refinement method

Hitachiite (this study)

Indices range of h, k, l
Weighting scheme
No. of variables
Reflection/Parameters ratio
Rint (%)
Residuals: R1 (%), R (all) (%)
Residuals: wR2 (%)
GoF
Δρmax, Δρmin (e– Å–3)

Pb5Bi2Te2S6
0.05 × 0.02 × 0.02
Trigonal, P
3m1
a = 4.2200(13), c = 27.02(4)416.7(7)
1
7.54
298
71.7

Pb1 octahedron
Pb1–S2 [x6]Pb2 octahedron
Pb2–S3 [x3]Pb2–S1 [x3]<Pb2–S>
Pb3 octahedron
Pb3–S1 [x3]Pb3–S2 [x3]<Pb3–S>

Synchrotron, λ = 0.70134 Å
60
XABS2 (Parkin et al., 1995)
1993, 246, 724
SuperFlip (Palatinus and Chapuis, 2007)
SHELXL97 (Sheldrick and Schneider,1997)−5 ≤ h ≤ 5, 0 ≤ k ≤ 6, –37 ≤ l ≤ 37
w = 1/[σ2(Fo2)]
22
11.18
10.8
7.38, 8.30
16.29
0.977
9.454, –4.413

Bi octahedron
Bi–S3 [x3]Bi–TeA [x3]<Bi–S/Te>Interlayer
TeA–TeA

Related minerals

2.958(14)Galena*Pb octahedron
Pb–S [x6]2.96582.938(17)3.001(14)2.970(16)2.953(13)2.994(15)2.974(14)3.028(18)3.025(4)3.027(11)3.773(9)Tetradymite**
Bi octahedron
Bi–S [x3]Bi–Te [x3]<Bi–S/Te>Interlayer
Te–Te

3.058
3.129
3.094
3.697

*Data from Noda et al. (1987); **Data from Harker et al. (1934)classification system (Strunz and Nickel, 2001). Makovicky (2006)
summarised the crystal structures of sulfide and related chalcogenide compounds. In his summary, the tetradymite series especially, isexpressed chemically as the extended selenides and tellurides of bismuth based on the structural classification of Bayliss (1991). The
fundamental structural unit of the tetradymite structure has anoctahedral double layer Bi2X3 (X = Te, Se and S). Considering thehigh amount of Pb in the chemical formula of hitachiite, it
seems to be similar to the lillianite (Pb3Bi2S6) series in 2.JA.20
and/or the galenobismutite (PbBi2S4) series in 2.JA.25 of sulfosalts(Strunz and Nickel, 2001). However, the crystal structure of hitachiite is definitely different from those of lillianite and galenobismutite, and so it cannot be classified to these groups.
The crystal structure of hitachiite is based on ABC-type closepacking of each single element atomic sheet stacked along thec axis and can be regarded as a layered structure (tetradymite
archetype) with a periodicity of ∼27 Å. The crystal structure ofhitachiite has five Pb, two Bi, two Te and six S sheets. There
are three Pb, one Bi, one Te and three S crystallographic sites.
The stacking sequence can be expressed as Te–Bi–S–Pb–S–Pb–

S–Pb–S–Pb–S–Pb–S–Bi–Te (Fig. 5). The crystal structure of hitachiite contains PbS6 and BiTe3S3 octahedra. Its crystal structure
can be viewed as composed from a galena and tetradymite unit
(Bi2Te2S) (Figs 5 and 6). The mean Pb–S and Bi–(Te, S) distancesin each octahedron are 2.958(14) Å for Pb1–S, 2.970(16) Å for
Pb2–S, 2.974(14) Å for Pb3–S and 3.027(11) Å for Bi–(Te, S).
These values are in good agreement with those observed in tetradymite (3.058 Å for Bi–S and 3.129 Å for Bi–Te; Harker et al.,1934) and that in galena (2.9658(8) Å for Pb–S; Noda et al.,1987). Also, the TeA–TeA interlayer distance is 3.773(9) Å andis consistent to those of tetradymite (3.697 Å for Te–Te, Harker
et al., 1934; 3.895–4.037 Å for Te–Te and Te–S, Pauling, 1975)
and the reported distance (3.65–3.70 Å for Te–Te) by
Makovicky (2006).
In comparison with the tsumoite (BiTe; P3m1; Shimazaki andOzawa, 1978) and the Pb-rich baksanite (Bi5PbTe2S3; P3m1; Bindi
and Cipriani, 2003) structures, hitachiite and tetradymite(Bi2Te2S; R3; Harker et al., 1934) structures lack the Bi–Bi double
layer (Fig. 5). As shown by Nakajima (1963), in selenides and tellurides of bismuth, there are four species with the tetradymite
archetype structure as Bi2TexSe3–x (x = 0, 1, 2 and 3). In contrast,
Kuznetsov and Kanishcheva (1970) showed that the compositional limit of tetradymite in the system Bi2Te3–Bi2S3 was
Bi2STe2–Bi2S1.3Te1.7. Considering the Te–S substitution, Pauling(1975) suggested that a partial Te–S interlayer could be allowedin the tetradymite structure. In order to form the tetradymite
archetype structure, it is key to have tetradymite unit (S–Bi–Te–

Table 4. Final atomic coordinates and displacement factors for hitachiite.

Pb1
Pb2
Pb3
Bi
S1
S2
S3
TeA
TeB

x

y

z

Occ.

Ueq / Uiso

U 11

U 22

U 33

U 23

U 13

U 12

0
⅓
⅔
0
0
⅓
⅔
⅓
⅓

0
⅔
⅓
0
0
⅔
⅓
⅔
⅔

½
0.24690(13)0.37352(14)0.11964(15)0.3118(8)0.4380(9)0.1862(11)0.0533(2)0.0044(10)

1
1
1
1
1
1
1
0.81(2)0.19(2)0.0127(13)0.0155(10)0.0155(10)0.0196(12)0.012(6)*0.008(4)*0.024(7)*0.0032(16)*0.0032(16)*0.015(2)0.0134(17)0.0145(18)0.0170(16)0.015(2)0.0134(17)0.0145(18)0.0170(16)0.009(4)0.020(3)0.018(3)0.025(3)0.00000.00000.00000.00000.00000.00000.00000.00000.0074(11)0.0067(9)0.0072(9)0.0085(8)* Uiso.

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738

Takahiro Kuribayashi et al.

Fig. 5. Crystal structures of hitachiite and related minerals: (a) tsumoite, BiTe; (b) hitachiite, Pb5Bi2Te2S6; and (c) tetradymite, Bi2Te2S.

Te–Bi–S), which has an anion–anion interlayer except for S–S(Fig. 5). Other related Pb-bearing minerals with tetradymite
archetype structure include rucklidgeite, PbBi2Te4 (Zhukova andZaslavskii, 1972) and kochkarite, PbBi4Te7 (Talybov andVainshtein, 1962; Shelimova et al., 2004). However, contrary tothat, crystal structures of galenobismutite and mozgovaite,
PbBi4S7 are different. These structural differences imply that it
is important to consider the role of Se and Te in the structure
due to the differences of chemical properties from S.
The chemical formulae of hitachiite, saddlebackite and aleksite
lie on the join of Bi2Te2S–PbS (Fig. 3a). In the review of sulfosalt
systematics by Moëlo et al. (2008), the aleksite homologous series,
Pb(n–1)Bi2Ch(n+2), are described as layered sulfosalts related to thetetradymite archetype. Hitachiite can be related to this homologous series (n = 6). In the case of the originally proposed homologous series of PbnBi4Te4Sn+2 (Cook et al., 2007a), hitachiite
corresponds to the case of n = 10. However, the discovery of hitachiite means there are now three species having a similar
PbnBi2Te2Sn+1 formula with various Pb contents alongside aleksite and saddlebackite. This finding implies that the systematic
chemical formulae of these minerals should be expressedalternatively as Bi2Te2S·nPbS (i.e. as a homologous series in thetetradymite–galena join). To fully understand the structural systematics of the minerals within the system Bi2Te2S–PbS it isnecessary to know their crystal structure.

Based on the idea proposed by Imanov and Semiletov (1971)
for the number of layers in complex compounds, Liu andChang (1994) estimated that the stacking sequence of aleksite
was Te–Bi–S–Pb–S–Bi–Te (Z = 6) using its c periodicity(∼79 Å); the stacking sequence of saddlebackite may correspondto Te–Bi–S–Pb–S–Pb–S–Bi–Te (Z = 2). With respect to theinner anionic layers of tetradymite archetype structures,
Nakajima (1963) suggested that the inner positions of thestacking sequence exhibit more ionic bonding. Similarly, Liu
and Chang (1994) pointed out important characteristics of thelead and bismuth chalcogenide with the layer-type structure liketetradymite: (1) PbX6 octahedral layers form the central part of
the unit stacks; (2) PbX6 octahedra should be regular, and thetwo X layers above and below the Pb layer should show thesame composition; and (3) on the basis of the tetradymite structure, if two or more chalcogen elements are present, the smaller
one should occupy the inner layer of the unit stacks. The structureof hitachiite seems to satisfy these suggestions.
This homologous series can be structurally characterised bystating that the tetradymite unit (Bi2Te2S, S–Bi–Te–Te–Bi–S)
sandwiched the galena (S–Pb–S) units by sharing an S layer(Fig. 5). As the details of crystal structures of aleksite (n = 1)
and saddlebackite (n = 2) are still unknown, their structures
must await further studies to discern their structural relations.
Hitachiite plays an important role in clarifying the structural

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Mineralogical Magazine

Fig. 6. Ideal structure of hitachiite illustrated using galena-like and tetradymite-likestructural units.

systematics of these minerals as for its peculiar distribution of Pb/
Bi and Fe in the structure and for the site preference of minor
elements such as Fe, Sb and Se.
Acknowledgements. We are grateful to Drs. Leverett, Bindi, and an
anonymous reviewer for valuable and constructive comments on revising
our manuscript. We sincerely thank Mr. Y. Itoh and Mr. Ohyama of theTechnical Division, School of Science, Tohoku University for polishing thesample and making thin sections of hitachiite. This study was partially
supported by the Grant of KEK (PAC. No. 2017G137).
Supplementary material. To view supplementary material for this article,
please visit https://doi.org/10.1180/mgm.2019.45.

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