Mineralogical Magazine, June 2013, Vol. 77(4), pp. 475–483

Weissite from Gambatesa mine, Val Graveglia, Liguria,
Italy: occurrence, composition and determination of thecrystal structure
L. BINDI1,2*, C. CARBONE3, D. BELMONTE3, R. CABELLA3 AND R. BRACCO4
1

Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Via G. La Pira 4, I-50121 Florence, Italy
CNR Istituto di Geoscienze e Georisorse, Sezione di Firenze, Via G. La Pira 4, I-50121 Florence, Italy
3
Dipartimento di Scienze della Terra, dell’Ambiente e della Vita, Università degli Studi di Genova, Corso Europa
26, I-16132 Genoa, Italy
4
Via Montenotte 18, I-17100 Savona, Italy
2[Received 23 April 2013; Accepted 5 May 2013; AE: A. Pring]
ABSTRACT

Weissite, Cu2 xTe (x & 0.21), a very rare copper telluride, occurs in a sample from the Gambatesa mine,
Val Graveglia, Liguria, Italy, where it occurs as purplish black anhedral grains up to 0.1 mm in length andshows a black streak. No cleavage is observed and the Vickers hardness (VHN100) is 142 kg/mm2.
Weissite is dark bluish black, weakly pleochroic, and moderately anisotropic in bluish tints. Reﬂectancepercentages in air for Rmin and Rmax are 37.0, 38.4 (471.1 nm), 33.2, 34.2 (548.3 nm), 31.2, 32.1
(586.6 nm), and 28.6, 31.0 (652.3 nm), respectively.
Weissite is trigonal and belongs to the space group P3m1 with the following unit-cell parameters: a =8.3124(7) Å, c = 21.546(1) Å, V = 1289.3(2) Å3, and Z = 24. Electron microprobe analyses gave thechemical formula (Cu1.62Ag0.04Au0.04Fe0.04Sb0.04)S=1.78(Te0.96S0.02Se0.02). The crystal structure has beensolved and reﬁned to R = 1.95%. It consists of Cu and Te polyhedra forming complex crystal-chemical
environments as is typical of many intermetallic compounds. The exceedingly short bond distances
observed among the metals are discussed in relation to other copper tellurides and pure metals.
K EY WORDS : weissite, vulcanite, rickardite, tellurides, Val Graveglia, Italy.

Introduction
W EISSITE , Cu 2 x Te, is a rare mineral ﬁrst
described by Crawford (1927) during a study ofcopper tellurides from the Good Hope andMammoth Chimney mines at Vulcan, Gunnison
County, Colorado, USA. The mineral was later
studied by Thompson (1949), who carried out an
X-ray powder diffraction study and pointed out
the crystallographic and chemical differenceswith rickardite, Cu3 xTe2. By analogy with thesynthetic compounds of the system Cu Te(Patzak, 1956; Blachnik et al., 1983), weissite* E-mail: luca.bindi@unifi.it
DOI: 10.1180/minmag.2013.077.4.07# 2013 The Mineralogical Society

was considered to be hexagonal, with a = 12.54
and c = 21.71 Å, and this description has persisted
in the mineralogical literature (e.g. Anthony et al.,1990) as well as in several mineralogical
databases. Some years later, Baranova et al.
(1974) clariﬁed the problem performing thestructure determination of bIII by means ofelectron diffraction data, a synthetic compoundwith chemical formula Cu1.81Te and, therefore,
considered the analogue of weissite. On this basis,
Bayliss (1990) revised the unit cell and the crystal
symmetry of weissite reporting the mineral as
trigonal, with a & 8.3 and c & 21.71 Å.
However, Pashinkin and Fedorov (2003) recently
re-investigated all compounds in the system
Cu Te carefully and demonstrated that several

L. BINDI ET AL.

commensurate superstructures can occur for theCu2 xTe weissite-like compounds. Until now, no
structural data have been reported for natural
weissite. Furthermore, although correct (seebelow), the trigonal structural model obtained by
Baranova et al. (1974) for synthetic Cu1.81Te hasa high R index (17.8%). To help resolve concerns
relating to the physicochemical parameters ofweissite, crystal structure data, together withphysical and chemical data, are presented here.
Occurrence and physical and opticalproperties
The sample containing the weissite crystal used inthis study (Fig. 1) was found in 1998 in the dumpsof the Gambatesa mine (Val Graveglia, northern
Apennines, Liguria, Italy). The mineral occurs
within late quartz veins cross-cutting red Jurassic
cherts of the ‘‘Diaspri di Monte Alpe’’ Formation,
which generally hosts Mn orebodies (Cabella etal., 1998). The formation of secondary veins in
the braunite-rich ore is genetically related to atectonometamorphic overprint of the ophiolitic
sequences during Late Cretaceous–Early
Cenozoic at prehnite-pumpellyite facies conditions (T = 27525ºC; P = 2.50.5 kbar; Lucchetti
et al., 1990).
Weissite was identiﬁed because of the presenceof olive-green patches of secondary minerals of
mcalpineite (Carbone et al., 2013). In the sample,
weissite forms purplish black grains and veins in
fractures of quartz up to a few mm thick, whereas
its alteration products occur both as vein ﬁllings
and botryoidal aggregates on the faces of welldeveloped quartz crystals. Minor chalcocite and

FIG. 1. Weissite from the Gambatesa mine as iridescent
black grains in quartz. Picture 1.5 mm wide.

malachite are found rarely but not intimately
associated with Cu-Te minerals.
The mineral exhibits a subhedral to anhedralgrain morphology, and does not show any
inclusions of, or intergrowths with, otherminerals. The maximum grain size of weissite is~100 mm. It has a black streak and it is opaque intransmitted light and exhibits a metallic lustre. No
cleavage is observed and the fracture is uneven.
Micro-indentation measurements carried out
with a VHN load of 100 g give a mean value of
142 kg/mm2 (range: 137 151) corresponding to a
Mohs hardness of ~3.
In plane-polarized incident light, weissite isdark bluish black in colour, moderately bireﬂectant and very weakly pleochroic from light grey toa slightly greenish grey. Between crossed polars,

TABLE 1. Electron microprobe analyses (means, ranges and standard deviations) and atomic ratios (on the basisof one Te atom) for weissite.

Cu
Ag
Au
Fe
Sb
Te
S
Se
Total

Wt.%

Rangess

Atoms

Atomic ratios

41.50
1.80
3.30
0.94
2.04
49.15
0.27
0.66
99.66

39.55 41.99
1.55 2.01
3.02 3.57
0.77 1.11
1.85 2.29
48.55 50.21
0.12 0.35
0.44 0.82
98.70 100.11

0.16
0.03
0.05
0.03
0.04
0.20
0.02
0.04

Cu
Ag
Au
Fe
Sb
Te
S
Se
Satoms

1.62
0.04
0.04
0.04
0.04
0.96
0.02
0.02
1.78

476

WEISSITE FROM LIGURIA

it is very weakly anisotropic with greyish to lightblue rotation tints. Internal reﬂections are absent
and there is no optical evidence of growthzonation.
Reﬂectance measurements were performed in
air by using an MPM-200 Zeiss microphotometerequipped with a MSP-20 system processor on a
Zeiss Axioplan ore microscope. The ﬁlament
temperature was ~3350 K. An interference ﬁlter
was adjusted, in turn, to select four wavelengths formeasurement (471.1, 548.3, 586.6 and 652.3 nm).
Readings were taken for specimen and standard(SiC) maintained under the same focus conditions.
The diameter of the circular measuring area was
0.1 mm. Reﬂectance percentages in air for Rminand Rmax are 37.0, 38.4 (471.1 nm), 33.2, 34.2

(548.3 nm), 31.2, 32.1 (586.6 nm) and 28.6, 31.0
(652.3 nm), respectively.
Chemical composition
A preliminary chemical analysis using energy
dispersive spectroscopy, performed on the same
crystal fragment used for the structural study, did
not indicate elements (Z > 9) other than Cu, Te
and very minor Ag, Au, Fe, Sb, Se and S. The
chemical composition was then determined using
a Jeol JXA-8600 electron microprobe.
Concentrations of the major and minor elements
were determined at an accelerating voltage of
20 kV and a beam current of 40 nA, with variablecount times: 30 s were used for Cu and Te and

TABLE 2. Crystallographic data and reﬁnement parameters for weissite.
Crystal data
Ideal formula
Crystal system
Space group
Unit-cell parameters (Å)
Unit-cell volume (Å3)
Z
Crystal size (mm)Cu2 xTe (x = 0.21)
trigonal
P3m1 (#156)
8.3124(7) 21.546(1)1289.3(2)24
0.04560.05060.060

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

Oxford Xcalibur 3
298(3)
MoKa, 0.71073
69.87
50–11 to 11, –13 to 13, –34 to 34
o, 612, 1.00, 65
22680
2163 (0.034)
1224
99.3
ABSPACK (Oxford Diffraction, 2006)

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

Full-matrix least-squares on F2
2163/0/164
0.0195, 0.0323
0.0227, 0.0425
0.743
0.69, –2.02

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

477

L. BINDI ET AL.

60 s for the minor elements Ag, Au, Fe, Sb, Se
and S. For the wavelength dispersive spectroscopy analyses the following lines were used:
CuKa, TeLa, AgLa, AuMa, FeKa, SbLb, SeLa
and SKa. The estimated analytical precision is:0.30 for Cu and Te; 0.02 for Ag, Au, Sb andSe; 0.01 for Fe and S. The standards employed
were: metallic copper (Cu), synthetic Sb2Te3 (Sb,Te), metallic silver (Ag), metallic gold (Au),marcasite (Fe), synthetic PbSe (Se) and galena(S). The crystal fragment was found to behomogeneous within the limits of analyticaluncertainty. The average chemical composition,
together with ranges of wt.% of elements, isreported in Table 1. On the basis of S(Te+S+Se)= 1, the empirical formula is (Cu1.62Ag0.04Au0.04
Fe 0.04 Sb 0.04 ) S=1.78 (Te 0.96 S 0.02 Se 0.02 ), ideally
Cu2 xTe (x & 0.22).
Crystal-structure solution and reﬁnement
A small crystal fragment (45 mm650 mm6
60 mm) was selected for the single-crystal X-ray
diffraction study. The intensity data collection (seeTABLE 3. Atoms, Wyckoff letter, site occupancy, fractional atom coordinates (Å), and isotropic atomic
displacement parameters (Å2) for weissite.
Atom

Wyckoff

Site occupancy

x/a

y/b

z/c

Uiso

Cu1
Cu2
Cu3
Cu4
Cu5
Cu6
Cu7
Cu8
Cu9
Cu10
Cu11
Cu12
Cu13
Cu14
Cu15
Cu16
Cu17
Cu18
Cu19
Cu20
Cu21
Cu22
Cu23
Cu24
Te1
Te2
Te3
Te4
Te5
Te6
Te7
Te8
Te9
Te10
Te11
Te12

6e
1c
3d
1b
1a
3d
3d
3d
1b
1a
1c
3d
3d
1a
3d
1c
3d
1b
1a
3d
3d
3d
1b
1a
1a
3d
3d
1b
1a
3d
3d
1a
1b
3d
3d
1a

Cu0.17
Cu1.00Cu1.00Cu1.00Cu1.00Cu1.00Cu0.50Cu1.00Cu1.00Cu1.00Cu1.00Cu0.50Cu1.00Cu1.00Cu1.00Cu1.00Cu1.00Cu1.00Cu1.00Cu1.00Cu1.00Cu1.00Cu1.00Cu1.00
Te1.00
Te1.00
Te1.00
Te1.00
Te1.00
Te1.00
Te1.00
Te1.00
Te1.00
Te1.00
Te1.00
Te1.000.4990(6)˜¯
0.8353(1)ˆ¯
00.4961(1)0.1620(2)0.8250(1)ˆ¯0˜¯
0.8310(2)0.16002(8)00.4954(1)˜¯
0.8350(1)ˆ¯
00.5049(1)0.1631(1)0.82801(8)ˆ¯
000.50500(5)0.83502(5)ˆ¯
00.50499(5)0.49705(6)0ˆ¯0.82500(5)0.49495(5)00.4990(6)ˆ¯
0.8353(1)˜¯
00.4961(1)0.1620(2)0.8250(1)˜¯
00.0010(4)0.04543(9)0.06099(7)0.06224(9)0.22505(8)0.22469(6)0.2540(1)0.27024(7)0.27094(6)0.32724(8)0.36849(8)0.4991(1)0.61992(6)0.67195(8)0.67486(7)0.69743(8)0.73079(7)0.73189(6)0.7779(1)0.77890(9)0.93206(8)0.93880(5)0.93969(9)0.99832(9)0.11395(4)0.11514(3)0.39005(3)0.39199(3)0.44201(4)0.44207(2)0.55693(4)0.55787(4)0.60892(4)0.60891(2)0.88400(3)0.88501(4)0.0370(9)0.0340(3)0.0406(2)0.0331(3)0.0329(3)0.0502(3)0.0511(5)0.0498(3)0.0323(3)0.0330(3)0.0322(3)0.0391(3)0.0399(2)0.0331(3)0.0506(3)0.0324(3)0.0506(3)0.0327(3)0.0329(3)0.0508(3)0.0501(3)0.0303(1)0.0334(3)0.0339(3)0.0331(2)0.0403(1)0.0405(1)0.0329(2)0.0330(2)0.0408(1)0.0507(2)0.0331(2)0.0336(2)0.0409(1)0.0405(1)0.0332(2)478

0.8310(2)0.16002(8)00.4954(1)ˆ¯
0.8350(1)˜¯
00.5049(1)0.1631(1)0.82801(8)˜¯
000.50500(5)0.83502(5)˜¯
00.50499(5)0.49705(6)0˜¯
0.82500(5)0.49495(5)0WEISSITE FROM LIGURIA

Table 2 for details) was carried out using an
Oxford Diffraction Xcalibur 3 single-crystal
diffractometer (enhanced X-ray source, X-ray
radiation MoKa, l = 0.71073 Å) ﬁtted with a
Sapphire 2 CCD detector. A total of 612 frames ofdata were collected at room temperature as eightsets of omega runs with an exposure time of 65 s
per frame and a frame width of 1.00º. Thisafforded an overall data collection of 22680
reﬂections (2163 unique). Data frames were
processed using the CrysAlis software package(Oxford Diffraction, 2006) running on the
Xcalibur 3 control PC. The program ABSPACK(Oxford Diffraction, 2006) was used for theabsorption correction. The merging R for thedata set decreased from 13.69% before theabsorption correction to 3.40% after this correction. Because of the close similarity of the unit cellfound with our instrument (i.e. a = 8.3124(7) Å,c = 21.546(1) Å, V = 1289.3(2) Å3) with thatreported by Baranova et al. (1974) (a = 8.37 Å, c =21.6 Å, V = 1310 Å3) for synthetic Cu1.81Te, we
decided to solve the structure in the space group
P3m1 as proposed by them. The positions of mostof the Cu and Te atoms were determined from athree-dimensional Patterson synthesis (Sheldrick,

TABLE 4. Anisotropic displacement parameters of the atoms for the weissite crystal.
Atom

U11

U22

U33

U12

U13

U23

Cu1
Cu2
Cu3
Cu4
Cu5
Cu6
Cu7
Cu8
Cu9
Cu10
Cu11
Cu12
Cu13
Cu14
Cu15
Cu16
Cu17
Cu18
Cu19
Cu20
Cu21
Cu22
Cu23
Cu24
Te1
Te2
Te3
Te4
Te5
Te6
Te7
Te8
Te9
Te10
Te11
Te12

0.031(2)0.0339(4)0.0405(4)0.0323(5)0.0337(5)0.0509(5)0.0510(8)0.0516(4)0.0342(5)0.0328(5)0.0324(4)0.0380(6)0.0402(3)0.0318(5)0.0482(4)0.0314(4)0.0522(5)0.0332(5)0.0328(5)0.0508(5)0.0501(4)0.0295(3)0.0325(5)0.0344(5)0.0331(3)0.0404(2)0.0413(2)0.0339(2)0.0336(3)0.0411(2)0.0518(3)0.0337(2)0.0344(3)0.0414(2)0.0407(2)0.0337(2)0.031(2)0.0339(4)0.0405(4)0.0323(5)0.0337(5)0.0509(5)0.0510(8)0.0516(4)0.0342(5)0.0328(5)0.0324(4)0.0380(6)0.0402(3)0.0318(5)0.0482(4)0.0314(4)0.0522(5)0.0332(5)0.0328(5)0.0508(5)0.0501(4)0.0295(3)0.0325(5)0.0344(5)0.0331(3)0.0404(2)0.0413(2)0.0339(2)0.0336(3)0.0411(2)0.0518(3)0.0337(2)0.0344(3)0.0414(2)0.0407(2)0.0337(2)0.046(2)0.0342(6)0.0415(4)0.0347(5)0.0313(6)0.0494(7)0.049(1)0.0461(5)0.0285(5)0.0335(6)0.0317(6)0.0419(6)0.0380(3)0.0359(7)0.0546(7)0.0344(6)0.0479(8)0.0316(6)0.0331(5)0.050(6)0.0498(6)0.0315(3)0.0353(5)0.0331(5)0.0331(3)0.0400(2)0.0393(2)0.0308(3)0.0319(3)0.0399(2)0.0479(3)0.0319(3)0.0319(3)0.0397(2)0.0400(3)0.0324(4)0.013(2)0.0170(2)0.0208(5)0.0162(2)0.0168(2)0.0257(6)0.024(1)0.0256(5)0.0171(2)0.0164(3)0.0162(2)0.0195(8)0.0192(4)0.0159(2)0.0234(6)0.0157(2)0.0266(6)0.0166(2)0.0164(2)0.0252(6)0.0248(5)0.0145(3)0.0162(3)0.0172(2)0.0165(1)0.0203(2)0.0209(2)0.0170(1)0.0168(1)0.0204(2)0.0256(3)0.0169(1)0.0172(1)0.0205(2)0.0202(2)0.0168(1)0.002(1)00.0002(2)00–0.0006(3)–0.0006(5)0.0001(3)0000.0002(4)–0.0003(2)0–0.0003(2)0–0.0002(2)00–0.0003(2)–0.0002(2)–0.0003(2)0000.0003(1)0.00016(9)000.00035(9)–0.0004(1)00–0.0004(1)–0.0004(1)0–0.002(1)0–0.0002(2)000.0006(3)0.0006(5)–0.0001(3)000–0.0002(4)0.0003(2)00.0003(2)00.0002(2)000.0003(2)0.0002(2)0.0003(2)000–0.0003(1)–0.00016(9)00–0.00035(9)0.0004(1)000.0004(1)0.0004(1)0479

L. BINDI ET AL.

FIG. 2. The crystal structure of weissite projected down [100]. The horizontal direction is the c axis. Cu and Te are
given as light blue and white spheres, respectively. The unit cell is outlined.

2008). A least-squares reﬁnement using theseheavy-atom positions and isotropic temperaturefactors yielded an R factor of 16.21%. Threedimensional difference Fourier synthesis yielded
the position of the remaining atoms. The fullmatrix least-squares program SHELXL-97(Sheldrick, 2008) was used for the reﬁnement of
the structure. The occupancy of all the atoms wereleft free to vary and three Cu atoms (i.e. Cu1, Cu7
and Cu12) were found partially occupied, as in themodel reported by Baranova et al. (1974). Then,
their occupancy was ﬁxed to the reﬁned values tolower the number of reﬁned parameters. The
introduction of anisotropic temperature factors for
all the atoms led to R = 1.95% for 1224 observed
reﬂections [Fo > 4s(Fo)] and R = 2.27% for all
2163 independent reﬂections. Neutral scattering
curves for Cu and Te were taken from theInternational Tables for X-ray Crystallography(Ibers and Hamilton, 1974). Inspection of thedifference Fourier map revealed that maximum
positive and negative peaks were 0.69 and 2.02
e /Å3, respectively. All the atoms were labelledwith the same nomenclature given by Baranova etal. (1974).
Experimental details and R indices are given in
Table 2. Fractional atomic coordinates andanisotropic-displacement parameters are shownin Tables 3 and 4, respectively. Structure factors(Table 5) and bond distances (Table 6) have been
deposited with the Principal Editor of
Mineralogical Magazine at http://www.minersoc.
org/pages/e_journals/dep_mat.html

phase of the system Cu Te. It can be considered
as an intermetallic compound and, therefore, theclassic polyhedral description is hardly applicable.
There are 24 independent Cu and 12 Te atoms inthe structure showing signiﬁcantly different
crystal-chemical environments (Table 7).
One of the most interesting structural peculiarities of the crystal structure of weissite, withrespect to that of vulcanite (Pertlik, 2001) andrickardite (Schutte and de Boer, 1993), is thepresence of exceedingly short bond distances
between metals. The shortest Cu Te distance inweissite of 2.308(2) Å (i.e. Cu19 Te12) is indeed
much shorter than 2.604(1) Å and 2.63(1) Åobserved in vulcanite (CuTe) and rickardite(Cu5 xTe2), respectively. A similar behaviour isobserved for the Cu Cu and Te Te contacts: theshortest Cu Cu distance (i.e. Cu14 Cu19) of
2.282(3) Å is shorter than that observed in metallic
copper (2.546 Å; Suh et al., 1988) and the shortest
Te Te distance (i.e. Te5 Te8) of 2.496(1) Å isshorter than that observed in native tellurium(Te Te = 2.835 Å; Cherin and Unger, 1967).

Description of the structure and discussion
The crystal structure of weissite (Figs. 2 and 3) is
topologically identical to that reported by
Baranova et al. (1974) for the synthetic bIII

FIG. 3. The crystal structure of weissite projected down[001]. The unit cell is outlined. Symbols and colours as
in Figure 2.

480

WEISSITE FROM LIGURIATABLE 7. Mean bond distances (Å) and coordination polyhedra for weissite.
Atom<Cu1–Te,Cu><Cu2–Te,Cu><Cu3–Te,Cu><Cu4–Te,Cu><Cu5–Te,Cu><Cu6–Te,Cu><Cu7–Cu><Cu8–Te,Cu><Cu9–Te,Cu><Cu10–Te,Cu><Cu11–Te,Cu><Cu12–Te><Cu13–Te,Cu><Cu14–Te,Cu><Cu15–Te,Cu><Cu16–Te,Cu><Cu17–Te,Cu><Cu18–Te,Cu><Cu19–Te,Cu><Cu20–Te,Cu><Cu21–Te,Cu><Cu22–Te,Cu><Cu23–Te,Cu><Cu24–Te,Cu><Te1–Cu><Te2–Cu><Te3–Cu,Te><Te4–Cu,Te><Te5–Cu,Te><Te6–Cu,Te><Te7–Cu,Te><Te8–Cu,Te><Te9–Cu,Te><Te10–Cu,Te><Te11–Cu><Te12–Cu>

Mean (Å)

Coordination

2.695
2.722
2.711
2.721
2.493
2.504
2.533
2.591
2.533
2.702
2.622
2.613
2.616
2.705
2.707
2.732
2.634
2.653
2.603
2.523
2.610
2.644
2.604
2.711
2.722
2.740
2.754
2.734
2.695
2.649
2.777
2.802
2.683
2.674
2.655
2.689

11-vertex polyhedron with 2Te and 9Cu
icosahedron with 3Te and 9Cu
bicapped square prism with 3Te and 7Cu
bicapped square prism with 3Te and 7Cu
8-vertex polyhedron with 1Te and 7Cu
trigonal prism with 1Te and 5Cu
pentagonal bipyramid with 7Cu
7-vertex polyhedron with 1Te and 6Cu
7-vertex polyhedron with 1Te and 6Cu
pseudo Frank-Kasper polyhedron with 4Te and 7Cutricapped trigonal prism with 6Te and 3Cu
8-vertex polyhedron wit 8Te
tricapped trigonal prism with 6Te and 3Cu
pseudo Frank-Kasper polyhedron with 4Te and 7Cu
pseudo Frank-Kasper polyhedron with 4Te and 7Cu
icosahedron with 3Te and 9Cu
8-vertex polyhedron with 1Te and 7Cu
7-vertex polyhedron with 1Te and 6Cutrigonal bipyramid with 1Te and 4Cu
trigonal prism with 1Te and 5Cutricapped trigonal prism with 3Te and 6Cutricapped trigonal prism with 3Te and 6Cu
bicapped square prism with 3Te and 7Cu
11-vertex polyhedron with 2Te and 9Cu
bipyramid with 5Cu
trigonal prism with 6Cu
7-vertex polyhedron with 3Te and 4Cu
tetrahedron with 3Te and 1Cu
8-vertex polyhedron with 4Te and 4Cu
7-vertex polyhedron with 4Te and 3Cu
tricapped trigonal prism with 4Te and 5Cu
11-vertex-polyhedron with 4Te and 7Cu
bicapped square prism with 3Te and 7Cu
bicapped square prism with 3Te and 7Cu
pentagonal bipyramid with 7Cu
8-vertex polyhedron with 8Cu

The reason for the formation of the superstructure characterizing the weissite structure (i.e.
a superstructure of the basic hexagonal substructure with a = 4.25 and c = 7.29 Å, Villars andCalvert (1985)), as well as those of most of thephases in the system Cu Te, is generally linked
to the mobility of the copper ions in different
valence states, Cu+ or Cu2+, in a rigid Te
framework. As documented by Pashinkin andFedorov (2003), the arrangement of the Cu ionsdepends on the composition of the phase andthermal history, which may lead to the formationof a superstructure. Such features make thestructural behaviour of weissite very similar to481

that of calaverite, AuTe2, where the displacive
modulation of the atoms is associated with avalence ﬂuctuation of Au+ and Au3+ (Schutte andde Boer, 1988; Bindi et al., 2009).
The origin of weissite is probably related tohydrothermal mobilization and concentration
processes along fractures. Hydrothermal ﬂuids
have the ability to carry signiﬁcant amounts of Te,
as supported by the close Au-Te association inepithermal deposits (Pals and Spry, 2003) andexperimental determinations as well (McPhail,
1995; Brugger et al., 2012). In the Val Graveglia
Mn-ores, the concentration of Te in the secondaryveins seems to occur under reducing conditions,

L. BINDI ET AL.

which are the same conditions responsible for theformation of the uncommon As-V parageneses
previously described from ore deposits in Val
Graveglia (Basso et al., 1992, 1994, 2003, 2005,
2008; Bindi et al., 2011).
Acknowledgements
The paper beneﬁted from the ofﬁcial reviews ofAllan Pring and Paul Spry.
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