Eur. J. Mineral.
2012, 24, 1069–1076
Published online July 2012

Chukhrovite-(Ca), Ca4.5Al2(SO4)F1312H2O, a new mineral species from the
Val Cavallizza Pb–Zn–(Ag) mine, Cuasso al Monte, Varese province, Italy
PIETRO VIGNOLA1, FRÉDÉRIC HATERT2,*, DANILO BERSANI3, VALERIA DIELLA1, PAOLO GENTILE4
and ANDREA RISPLENDENTE5
1

CNR, Istituto per la Dinamica dei Processi Ambientali, via Mario Bianco 9, 20131 Milano, Italy
Laboratoire de Minéralogie, Départment de Géologie, Universitè de Liège, B^atiment B18, Sart Tilman,
4000 Liège, Belgium*Corresponding author, e-mail: fhatert@ulg.ac.be3
Dipartimento di Fisica, Università di Parma, Viale G.P. Usberti 7/a, 43124 Parma, Italy
4
Dipartimento di Scienze Geologiche e Geotecnologie, Università di Milano-Bicocca, Piazzale della Scienza 4,
20126 Milano, Italy
5
Dipartimento di Scienze della Terra, Università degli Studi di Milano, via Botticelli 23, Milano 20133, Italy
2

Abstract: Chukhrovite-(Ca), Ca4.5Al2(SO4)F1312H2O, is the Ca-dominant species of the chukhrovite mineral group. It occurs at the Val
Cavallizza Pb–Zn–Ag mine, Cuasso al Monte, Varese province, Italy. Chukhrovite-(Ca) is found as low temperature hydrothermal
crystallizations covering the surfaces of brittle fractures crosscutting a marcasite and REE-bearing fluorite vein. Associated minerals
include marcasite, gypsum, and hydrated Fe oxides. This new calcium aluminofluoride forms sharp octahedra up to 150 mm in diameter.
Crystals are translucent to transparent, colourless to white, with a white streak and a vitreous lustre. Chukhrovite-(Ca) is isotropic with n ¼
1.432(1), and is non-fluorescent either under short-wave (254 nm) or long-wave (366 nm) ultraviolet light. The mineral is brittle witha Mohs hardness of 3.5(5), and without a distinct cleavage or fracture. Its density, calculated from the single-crystal unit-cellparameters and assuming 12 H2O molecules per formula unit, is 2.23 g/cm3. The empirical formula, based on 3 (Al þ S) atoms per
formula unit and calculated from an average of five selected point analyses, is: (Ca4.33Na0.11Fe0.03)4.47Al2.10(S0.90O3.72)
F13.105.98H2O, with the water content calculated by difference to 100 %. Chukhrovite-(Ca) is cubic with space groupFd3; its
single-crystal unit-cell parameters are a ¼ 16.749(1) Å and V ¼ 4698.6(1) Å3, for Z ¼ 8. The eight strongest lines in the X-ray powder
diffraction pattern are [d in Å (I/I0) hkl]: 9.665 (100) 111, 5.921 (31) 022, 5.053 (16) 113, 4.190 (10) 004, 3.226 (15) 333 and 115,
2.556 (10) 533, 2.182 (12) 355 and 137, 1.915 (17) 626. The mineral, which has been approved by the CNMNC under number IMA
2010-081, is named chukhrovite-(Ca), since it corresponds to the Ca-rich equivalent of chukhrovite-(REE) (REE ¼ Ce, Nd, Y), in
which REE are replaced by Ca.
Key-words: chukhrovite-(Ca), new mineral species, calcium aluminofluoride, chukhrovite group, Val Cavallizza mine, Cuasso al
Monte, central Southern Alps, Italy.

1. Introduction

yaroslavite, muscovite, and jarosite (Novikova, 1973;
Pekov, 1998). Its occurrence was also notified in Grube
Clara (Germany) by Walenta (1978), and, more recently, at
Gamskalgraben (Austria) by Niedermayr et al. (2008).
The REE-free mineral species meniaylovite, Ca4AlSi(SO4)F1312H2O, was described as white to yellowish crystals produced by volcanic exhalations of the Tolbachik
volcano (Kamchatka territory, Russia) and of the Eldfell
volcano (Heimaey island, Iceland) (Vergasova et al., 2004;
Mitolo et al., 2008). The last identified mineral species
belonging to the chukhrovite group is chukhrovite-(Nd),
Ca3(Nd,Y)Al2(SO4)F1312H2O, which forms colourless towhite crystals from 0.05 up to 0.4 mm diameter, associatedwith chukhrovite-(Y) in the Kara-Oba deposit (Pautov et al.,2005). These four mineral species are cubic with space

The chukhrovite group includes four extremely rare Caand REE-bearing aluminofluoride mineral species.
Chukhrovite-(Y), Ca3(Y,Ce)Al2(SO4)F1312H2O, was discovered in 1950 in the oxidized zone of the Kara-Oba
tungsten deposit (Kazakhstan), and described as colourless
to white cubo-octahedral crystals up to 1 cm diameter,
associated with halloysite, gearksutite, fluorite, creedite,anglesite, and ‘‘limonite’’ (Ermilova et al., 1960; Pekov,
1998). Chukhrovite-(Ce), Ca3(Ce,Y)Al2(SO4)F1312H2O,
was found for the first time at the Yaroslavskoye tin
deposit (Primorsk Territory, Russia), where it forms
milky-white cubo-octahedral crystals up to 1.5 mm indiameter, associated with fluorite, tourmaline, ralstonite,eschweizerbart_xxx

0935-1221/12/0024-2247 $ 3.60
DOI: 10.1127/0935-1221/2012/0024-2247# 2012 E. Schweizerbart’sche Verlagsbuchhandlung, D-70176 Stuttgart

1070

P. Vignola, F. Hatert, D. Bersani, V. Diella, P. Gentile, A. Risplendentegroup Fd3; their unit-cell parameters are 16.800(5),16.800(5), 16.722(2), and 16.759(3) Å, respectively.
In 1993, during a field campaign in the Val Cavallizza
mine, Cuasso al Monte, Varese province, north Italy, we
found octahedral colourless crystals covering the surfacesof brittle fractures crosscutting a marcasite and REE-bearing fluorite vein. Mineralogical analyses of these crystals
showed that they correspond to a REE-free calcium aluminofluoride belonging to the chukhrovite group. The
mineral was consequently named chukhrovite-(Ca), since
it corresponds to the Ca-rich equivalent of chukhrovite(REE) (REE ¼ Ce, Nd, Y), in which REE are replaced by
Ca. Both the mineral and the name were approved by the
IMA Commission on New Minerals, Nomenclature andClassification (IMA # 2010-081, Vignola et al., 2011).
This paper presents the mineralogical description of new
species chukhrovite-(Ca). The electron-microprobe, structural, optical, and spectroscopic analyses were performedon two co-type specimens extracted from the same handsample collected in 1993. These two co-types are stored in
the mineralogical collection of the Museum of Natural
History of Milano (Italy), catalogue number M37901, andin the mineralogical collection of the Laboratory of
Mineralogy of the University of Liège (Belgium), catalogue number 20383.

Fig. 1. Octahedral crystals of chukhrovite-(Ca).

empirical formula and single-crystal unit-cell parameters,
assuming 12 H2O molecules per formula unit, is 2.23 g/cm3.
The compatibility index, 1 – (Kp/Kc) ¼ 0.011, is superior.
For the compatibility calculations, we used the Ki constants
calculated for fluorides by Pauly (1982) (CaF2, AlF3, NaF),
as well as the constants calculated for oxides by Mandarino(1981) (FeO, CaO, SO3, H2O).

2. Occurrence, general appearance, andphysical properties
Chukhrovite-(Ca) was found in 1993 by two of the authors(P.V. and P.G.) in the Val Cavallizza mine, Cuasso al
Monte, Varese province, north Italy (45 540 0100 N;
8 510 4100 E). The Val Cavallizza Pb–Zn–(Ag) mineralization, discovered in 1869, was mined from 1901 to 1903 forPb and Ag (Bozzoli, 1905). The last survey workings,
operated by the RiMin society, date back to the
1951–1953 period; then the mine was completely abandoned. Chukhrovite-(Ca) occurs as low temperature hydrothermal crystallizations covering the surfaces of brittle
fractures, crosscutting a marcasite and REE-bearing fluorite vein hosted by the late Hercynian NYF-miarolitic pink
porphyritic granite of Cuasso al Monte (Pezzotta et al.,2005). The mineral is associated with marcasite, REEbearing fluorite, gypsum, hydrated Fe oxides, as well as
minor galena and sphalerite.
Chukhrovite-(Ca) forms colourless to whitish, transparent to translucent, sharp octahedral crystals up to 100–150
mm diameter (Fig. 1). Twinning along the [001] axis, with arotation of 90 (iron cross law), is widespread, while spinel
law twins are rare. Chukhrovite-(Ca) is isotropic with n ¼
1.432(1) (measured with a microrefractometer spindlestage; Medenbach, 1985), shows a vitreous lustre, a white
streak, and is non-fluorescent either under short-wave (254nm) or long-wave (366 nm) ultraviolet light. The mineral isbrittle with a Mohs hardness of 3.5(5), and without a distinct
cleavage or fracture. Due to small grain size, the density was
not directly measured; the density value calculated from the

3. Chemical composition
Quantitative chemical analyses were performed onpolished thin sections of chukhrovite-(Ca), using a JEOL
JXA-8200 electron microprobe working in wavelengthdispersion mode, at the laboratory of the Department ofEarth Sciences, University of Milan. The system was operated using an accelerating voltage of 10 kV, a beam currentof 5 nA, a spot size of 5 mm, and a counting time of 30 s on
the peaks and 10 s on the background. Natural minerals(grossular for Si, Ca and Al, galena for S, omphacite forNa, and fayalite for Fe), as well as synthetic REE(PO4) (forREE) and RbMnF3 (for F), served as standards. The raw
data were corrected for matrix effects using the rZmethod from the JEOL series of programs.
The mean analytical results are reported in Table 1. H2O
was not determined directly due to the small amount ofmaterial, and the water content was calculated by difference to 100 wt%. This content significantly differs fromthat calculated from the structural data (see below), whichcorresponds to 31.80 wt% H2O; this difference is due towater loss under the electron beam, during the electronmicroprobe measurement. CO2 is absent from the mineral,
eschweizerbart_xxx

Chukhrovite-(Ca), a new mineral species

1071

Table 1. Electron-microprobe analysis of chukhrovite-(Ca).
Constituent

Wt%

Range

Stand. dev.

Cation numbers

SiO2
SO3
Al2O3
REE2O3
FeO
CaO
Na2O
F
H2Oa
O¼F
Total

0.03
10.64
15.72
b.d.l.
0.34
35.74
0.49
36.61
15.85
15.42100.00(0.00–0.07)(9.44–11.82)(13.13–17.07)–(0.01–0.98)(34.11–37.05)(0.16–0.77)(34.17–39.50)

0.02
0.52
0.85
–
0.26
0.78
0.18
1.35

Si apfu
S
Al
REE
Fe
Ca
Na
F
H2O

0.003
0.904
2.096
–
0.032
4.332
0.107
13.1005.979

Note: Average of 5 point analyses. Cation numbers were calculated on the basis of 3 (Al þ S) per formula unit.
The water content was calculated by difference to 100 %.

aas shown by the infrared and Raman spectra, as well as by
the structural data (see below). The empirical formula,calculated on the basis of 3 (Al þ S) atoms per formulaunit, is: (Ca4.33Na0.11Fe0.03)4.47Al2.10(S0.90O3.72)F13.10
5.98H2O. The simplified formula, in which the ideal
water content obtained from the structural data is used,corresponds to Ca4.5Al2(SO4)F1312H2O, which requires:
CaO 28.18, Al2O3 22.77, SO3 8.94, F 27.58, H2O 24.15, O F 11.61, total 100.00 wt%.

Table 2. X-ray powder diffraction data for chukhrovite-(Ca).

4. X-ray diffraction data and crystal structure
determination
The X-ray powder diffraction (XRPD) pattern of chukhrovite-(Ca) has been obtained using a high-resolution
Panalytical X’pert Pro X-ray powder diffractometerequipped with an X’Celerator-type detector at the
Department of Geological Sciences and Geotechnologiesof the University of Milan-Bicocca. Operating conditions
were: Ni-filtered CuKa radiation, 40 kV, 40 mA, 2y-range
from 5 to 105 , step size 0.017 2y, counting time 300 s
per step. Silicon NIST 640c was used as internal standard,
and the refinement of unit-cell parameters, as well as
indexing of reflections, were performed using the leastsquares indexing program CELREF 3, beta version(LMGP Suite of Programs for the interpretation of X-ray
Experiments, by Jean Laugier and Bernard Bochu, ENSP/
Laboratoire des Matériaux et du Génie Physique. http://
www.inpg.fr/LMGP). The refined unit-cell parameter for
space group Fd3 is a ¼ 16.736(7) Å, and V ¼ 4687.6(3) Å3,
for Z ¼ 8. The complete list of indexed reflections isreported in Table 2. The eight strongest measured lines
are [d in Å (I/I0) hkl]: 9.665 (100) 111, 5.921 (31) 022,
5.053 (16) 113, 4.190 (10) 004, 3.226 (15) 333 and 115,
2.556 (10) 533, 2.182 (12) 355 and 137, 1.915 (17) 626.
The X-ray structural study was carried out on an Oxford
Diffraction Gemini PX Ultra 4-circle diffractometerequipped with a Ruby CCD-area detector, on a chukhrovite-(Ca) crystal measuring 120 mm in length. Forty frameswith a spatial resolution of 1 were collected by the j/o

I/I0

dmeas

dcalca

100
31
16
7
10
3
6
15
2
4
4
7
10
,1
6
2
7
12
1
1
2
17
,1
1
6
1
7
5
1
,1
1
2
1
1
1
1
,1
,1
,1
,1
2

9.665
5.921
5.053
4.841
4.190
3.842
3.418
3.226
2.963
2.831
2.794
2.650
2.556
2.530
2.413
2.346
2.240
2.182
2.031
1.974
1.927
1.915
1.874
1.840
1.829
1.787
1.754
1.640
1.613
1.562
1.511
1.416
1.358
1.281
1.254
1.250
1.224
1.207
1.182
1.129
1.092

9.663
5.917
5.046
4.831
4.184
3.840
3.416
3.221
2.959
2.829
2.789
2.646
2.552
2.523
2.416
2.344
2.237
2.179
2.030
1.972
1.933
1.920
1.871
1.837
1.826
1.784
1.755
1.641
1.611
1.561
1.509
1.415
1.358
1.280
1.251
1.251
1.224
1.208
1.183
1.131
1.092

hkl
111
022
113
222
004
313
224
3 3 3, 1 1 5
044
315
244
206
533
226
444
1 5 5, 1 1 7246
3 5 5, 1 3 7446
2 2 8, 6 0 6
5 1 7, 5 5 5626048
5 3 7, 1 1 9
428
466
913
10 0 2, 2 6 8
6 6 6, 2 2 10539
7 5 7, 11 1 1
6 2 102 2 12, 10 4 6
5 5 11, 3 9 9, 11 1 7, 1 1 13
7 7 9, 11 3 7
3 1 139 5 9, 3 3 13888
14 0 2, 6 8 10, 10 0 10
1 7 13, 11 7 7, 13 5 515 1 3

Note: aUnit-cell parameter refined from the X-ray powder data: a ¼
16.736(7) Å. The bold characters indicate the 8 most intense peaks.
eschweizerbart_xxx

1072

P. Vignola, F. Hatert, D. Bersani, V. Diella, P. Gentile, A. Risplendentescan technique, with a counting time of 1.5 s per frame, in
the range 6.88 , 2y , 52.60 . A total of 1064 reflections
were extracted from these frames, corresponding to 365
unique reflections. The unit-cell parameter refined fromthese reflections is a ¼ 16.749(1) Å (V ¼ 4698.6(1) Å3),and is in good agreement with that refined from the X-ray
powder data. Data were corrected for Lorentz, polarisation
and absorption effects, the latter with an empirical method
using the SCALE3 ABSPACK scaling algorithm includedin the CrysAlisRED package (Oxford Diffraction, 2007).
The crystal structure of chukhrovite-(Ca) (Fig. 2) was
refined in space group Fd3. The starting atomic coordinates
were those of synthetic Ca-rich chukhrovite (Mathew et al.,1981), and scattering curves for neutral atoms, together withanomalous dispersion corrections, were taken from theInternational Tables for X-ray Crystallography, Vol. C(Wilson, 1992). In the final refinement cycle, all atoms
were refined anisotropically, except the hydrogen atoms
which were refined isotropically. The final R1 value is0.0466. Further details concerning the intensity data collection and refinement are listed in Table 3; atomic coordinates, site occupancy factors, and anisotropic displacement
parameters are reported in Table 4; bond distances are presented in Table 5.
The structure can be described as a compact assembly of
AlF6 octahedra, SO4 tetrahedra, and large Ca sites (Fig. 2).
The Ca sites are surrounded by F atoms and water molecules, forming distorted octahedra [Ca(2), bond distances
2.190–2.629 Å] or distorted pentagonal bipyramids [Ca(1),bond distances 2.317–2.455 Å] (Table 5). These Ca sites
are connected together by corner- or edge-sharing, and areconnected to the AlF6 regular octahedra (Al–F ¼ 1.803 Å)by corner-sharing. The SO4 tetrahedra (S–O ¼ 1.481 Å)occur within cavities in the structure, and are linked via
hydrogen bonds to the water molecules (Fig. 3). Both

Table 3. Experimental details for the single-crystal X-ray diffraction
study of chukhrovite-(Ca).
Crystal shape
Crystal size (mm)Crystal coloura (Å)
Vol. (Å3)
Space group
Z
Diffractometer
Operating conditions
Radiation (Å)
Scan mode
2ymin., 2ymax.
Range of indicesMeasured intensities
Unique reflections
Observed [I . 2s(I)]reflections
Absorption corrections
m (mm1)
l.s. refinement program
Refined parameters
R1 (Fo . 2s(Fo))
R1 (all)wR2 (all)S (goodness of fit)
Max D/s in the last l s.
cycle
Max peak and hole in the
final DF map (e/Å3)

Octahedron
0.120
Colourless
16.749(1)4698.6(1)Fd3
8Oxford Diffraction Gemini PX Ultrawith Ruby CCD-area detector
50 kV, 40 mA
MoKa (l ¼ 0.7107 Å)
j/o scan
6.88 , 52.60
11  h  17, 19  k  14,16  l  6
1064
365
332
Empirical (SCALE3 ABSPACK
scaling algorithm)
1.362
SHELX-97 (Sheldrick, 2008)
43
0.03990.04660.12391.014
0.000
þ 0.529 and 1.014

hydrogen atoms of the asymmetric unit are involved inhydrogen bonds: each water molecule is consequently
hydrogen bonded to an oxygen atom of the SO4 ion, andto a fluorine atom of the AlF6 octahedron (Fig. 3).
Refinement of the site occupancy factor for the Ca(2)site indicates that this site is only partially occupied by Ca,
thus explaining the relatively high displacement parameters observed (Table 4). This low site population of ca.
9 % corresponds to 0.55 atoms per formula unit (a.p.f.u.),and is in good agreement with the chemical composition of
the mineral. Indeed, the structural data indicate the presence of 4 Ca a.p.f.u. on the Ca(1) site, and of 0.55 Ca
a.p.f.u. on the Ca(2) site, thus totalizing an amount of 4.55
Ca atoms, very close to the 4.47 (Ca þ Na þ Fe) a.p.f.u.
measured with the electron microprobe. Bond-valencesums, calculated from the values of Brown & Altermatt(1985), are 2.99 (Al), 5.89 (S), 1.86 (Ca(1)), and 1.88
(Ca(2)); their good fit with the ideal values confirm thereliability of the assigned site populations.

5. Spectroscopic properties
Fig. 2. The crystal structure of chukhrovite-(Ca), projected along thea axis. The AlF6 octahedra are white, the Ca polyhedra are light grey,
and the SO4 tetrahedra are dark grey.
eschweizerbart_xxx

The infrared spectrum of chukhrovite-(Ca) (Fig. 4) wascollected with a Nicolet NEXUS spectrometer, in the0.0019 (2)0.004 (6)0.0031 (5)000.0031 (8)0.002 (1)0.018 (1)0.0019 (2)00.0031 (5)000.0021 (8)0.002 (1)0.002 (1)Al–F(2) ( 6)
Ca(1)–F(2) ( 3)
Ca(1)–F(1)
Ca(1)–OW ( 3)
H(1)–OW
OW–O

0.0205 (5)0.06 (1)0.0174 (6)0.0269 (8)0.017 (1)0.033 (1)0.031 (1)0.031 (2)0.0205 (5)0.041 (9)0.0174 (6)0.0269 (8)0.017 (1)0.024 (1)0.031 (1)0.055 (2)0.0205 (5)0.06 (1)0.0174 (6)0.0269 (8)0.017 (1)0.030 (1)0.031 (1)0.034 (2)0.0205 (5)0.052 (6)0.0174 (6)0.0269 (8)0.017 (1)0.0290 (7)0.031 (1)0.0401 (8)0.08 (2)0.09 (2)

S–O ( 4)
Ca(2)–OW ( 2)
Ca(2)–F(2) ( 2)
Ca(2)–OW0 ( 2)
H(2)–OWOW–F(2)

1.481 (4)2.190 (6)2.39 (1)2.629 (6)0.88 (1)2.819 (4)

6. Discussion
Chukhrovite-(Ca) belongs to the chukhrovite group (Danaclassification 12.01.05, Halides – Compound halides withmiscellaneous anions – Chukhrovite group. Strunz classification 03.CG.10, Halides – Complex halides –Aluminiofluorides with CO3, SO4, PO4), and corresponds
to the Ca-rich equivalent of chukhrovite-(REE) (REE ¼
Ce, Nd, Y) [Ca3(REE)Al2(SO4)F1312H2O] in which REE
are replaced by Ca, according to the substitution mechanism 0.5 & þ 1 REE3þ ¼ 0.5 Ca2þ þ 1 Ca2þ. Chukhrovite(Ca) also corresponds to the Al-rich equivalent of meniaylovite [Ca4AlSi(SO4)F1312H2O], in which calcium isinserted according to the substitution mechanism 0.5 &þ Si4þ ¼ 0.5 Ca2þ þ Al3þ.
All members of the chukhrovite mineral group crystallize in space group Fd3, with unit-cell parameters decreasing from the REE-bearing members to chukhrovite-(Ca).
The shortest unit-cell parameter belongs to menyailovite(Table 6). X-ray powder diffraction patterns of chukhrovite-group minerals are similar, with the most intense peaklocated around d ¼ 9.70 Å, except for chukhrovite-(Y) for
which the most intense peak is located at d ¼ 2.193 Å.
Interestingly, only chukhrovite-(Ca) shows two fairly
intense peaks at d ¼ 5.053 and 1.915 Å (Table 6).

0.29285 (4)
0.375
0.5
0.125
0.375
0.3400 (1)0.0740 (1)0.2436 (2)0.213 (3)0.213 (4)0.29285 (4)0.6030 (9)
0.5
0.125
0.375
0.4494 (1)0.0740 (1)0.3071 (2)0.276 (4)0.350 (4)1/3
0.046(3)
1/6
1/12
1/12
1
1/3
1
1
1

1.803 (2)2.317 (2)2.383 (1)2.455 (3)0.84 (1)2.819 (3)400–4000 cm1 region. Absorption bands corresponding tovibrations of the SO4 group are located at 864 (n1 SO4),
1077, and 1165 cm1 (n3 SO4), whereas H2O bending
vibrations occur at 1618 cm1, and H2O stretching modes
at 3233, 3349, 3504, and 3631 cm1. Starting from these
H2O stretching wavenumbers, the correlation established by
Libowitsky (1999) served to estimate the OW . . . O distances between oxygen atoms involved in hydrogen bonds.
These distances are in the range 2.72–2.90 Å, in very good
agreement with the OW . . . O distance of 2.819(3) Åobserved by single-crystal X-ray diffraction (Table 5).
The Raman spectrum (Fig. 5) was collected in the
100–3600 cm1 region using a Jobin-Yvon Horiba
Labram spectrometer (linearly-polarized He–Ne laser, l ¼
632.8 nm), equipped with an Olympus microscope. The
spectrum is characterized by absorption bands related to
the vibration of the sulphate group, at 449 (n2 SO4), 553 (n4SO4), 977 (n1 SO4), and 1112 cm1 (n3 SO4). Vibrations of
the water molecules occur at 1632 (H2O bending), 3270,
3440, 3470, and 3560 cm1 (H2O stretching). Low frequency bands, between 181 and 430 cm1, are attributed tocations and lattice modes.

0.29285 (4)0.125
0.5
0.125
0.375
0.2197 (1)0.0740 (1)0.1556 (2)0.132 (4)0.151 (4)
32 e
48 f
16 d
8a
8b
96 g
32 e
96 g
96 g
96 g
Ca(1)
Ca(2)
Al
S
F(1)
F(2)
O
O(W)
H(1)
H(2)

1073

Table 5. Interatomic distances (Å) for chukhrovite-(Ca).

0.0019 (2)00.0031 (5)000.0104 (8)0.002 (1)0.002 (2)

U12
U13
U23
U33
U22
U11
Ueq
S.O.F.
zyx
Wyckoff
Atom

Table 4. Final fractional atom coordinates, anisotropic displacement parameters (Å2), and site occupancy factors (S.O.F.) for chukhrovite-(Ca).

Chukhrovite-(Ca), a new mineral species

eschweizerbart_xxx

1074

P. Vignola, F. Hatert, D. Bersani, V. Diella, P. Gentile, A. Risplendente

Fig. 3. The hydrogen bonding scheme in the crystal structure of chukhrovite-(Ca). Large black atoms ¼ Al, small black atoms ¼ H, large grey
atoms ¼ Ca, small grey atoms ¼ S, large white atoms ¼ F, and small white atoms ¼ O and OW. The hydrogen bonds are dotted.

Compared to the structural data published for the synthetic Ca4AlSi(SO4)F1312H2O compound (Mathew
et al., 1981), the sample of chukhrovite-(Ca) investigatedherein shows a supplementary Ca(2) position, located at
0.125 0.375 0.6030(9) (Table 1). This supplementary
Ca position can be explained by the large Ca-content of
the natural sample, which reaches 4.43 Ca a.p.f.u. (seeabove). The topology of this site (Fig. 2 and 3) corresponds to a distorted octahedron, in which Ca is coordinated by 4 water molecules and two F(2) atoms (Table 5).
This coordination polyhedron is significantly different
from that observed around the 7-coordinated Ca(1)atom, which rather corresponds to a distorted pentagonal
bipyramid (Fig. 2 and 3).

Fig. 4. Infrared spectrum of chukhrovite-(Ca).

Acknowledgements: We acknowledge André-Mathieu
Fransolet and two anonymous reviewers for the fruitful
discussions and helpful suggestions. Many thanks are due
to Johan Wouters (Namur, Belgium), for his help during
the 4-circle X-ray diffraction measurements, as well as toOlaf Medenbach (Bochum, Germany), for the determination of the refractive index of chukhrovite-(Ca). The
Department of Earth Sciences and Geotechnologies of
University of Milan-Bicocca is thanked for providing the
X-ray powder diffraction facility. This work was financially supported by the Istituto per la Dinamica dei
Processi Ambientali (IDPA) of the Italian National
Research Council (CNR) (Research Project TA.P04.036‘‘Strategie di valutazione e valorizzazione di riserve
idriche e di georisorse territoriali’’). Frédéric Hatert thanks
the FRS-F.N.R.S. (Belgium) for a position of ‘‘Chercheur
qualifié’’.

Fig. 5. Raman spectrum of chukhrovite-(Ca).
eschweizerbart_xxx

Ca3YAl2(SO4)F1312H2O
Fd3
16.800(5)8–––4.256 (70)3.261 (90)2.843 (80)2.664 (70)2.572 (90)–2.193 (100)–1.834 (100)1.684 (80)2.34(7)1.43(1)
3
Colourless, white, lilac{100}{111}Ca4.5Al2(SO4)F1312H2O
Fd3
16.749(1)89.665 (100)5.921 (31)5.053 (16)4.190 (10)3.226 (15)2.831 (4)2.650 (7)2.556 (10)2.240 (7)2.182 (12)1.915 (17)1.829 (6)–2.25 (calc.)
1.432(1)3.5(5)
Colourless{111}

Ideal formulaSpace groupa (Å)Z
Strong X-ray lineseschweizerbart_xxx

Ca3CeAl2(SO4)F1312H2O
Fd3
16.800 (5)89.75 (100)5.93 (80)–
4.20 (50)
3.22 (70)––
2.56 (60)
2.24 (50)
2.17 (60)–1.824 (50)––
1.443(2)–White–

Chukhrovite-(Ce)[3, 4]
Ca3NdAl2(SO4)F1312H2O
Fd3
16.759(3)89.7 (100)
5.92 (70)––3.22 (80)––2.555 (70)2.240 (50)
2.180 (60)–
1.827 (50)–2.42(3)1.443(2)
3.5–4
Colourless, white{100}{111}

Chukhrovite-(Nd)[5]Note: [1] Ermilova et al. (1960), [2] Fleischer (1960), [3] Walenta (1978), [4] Fleischer et al. (1980), [5] Pautov et al. (2005), [6] Vergasova et al. (2004).

DensitynHardness
ColourMorphology

Chukhrovite-(Y)[1, 2]

Chukhrovite-(Ca)This work

MineralReference

Table 6. Comparison of the physical properties for minerals of the chukhrovite group.

Ca4AlSi(SO4)F1312H2O
Fd3
16.722(2)89.63 (100)5.91 (70)–4.173 (40)3.219 (70)––2.551 (70)2.235 (50)
2.178 (80)–1.824 (50)
–
2.25
1.430
–
–
–

Menyailovite[6]

Chukhrovite-(Ca), a new mineral species
1075

1076

P. Vignola, F. Hatert, D. Bersani, V. Diella, P. Gentile, A. Risplendente

Novikova, M.I. (1973): Occurrence of chukhrovite in Siberia.
Zapisky Vseross. Mineral. Obshch. (Proc. Russ. Miner. Soc.),
102, 200–202 (in Russian).
Oxford Diffraction. (2007): CrysAlis CCD and CrysAlis RED, version 1.71. Oxford Diffraction, Oxford.
Pauly, H. (1982): Gladstone-Dale calculations applied to fluorides.
Can. Mineral., 20, 593–600.
Pautov, L.A., Bekenova, G.K., Karpenko, W.Y., Agakhanov, A.A.
(2005): Chukhrovite-(Nd), Ca3(Nd,Y)Al2(SO4)F1310H2O, a
new mineral. New data on minerals, Vol. 40. Russian
Academy of Sciences and Fersman Mineralogical Museum,
Ocean Pictures éd, Moscow, 168 p.
Pekov, I.V. (1998): Minerals first discovered on the territory of theformer Soviet Union. 1st Edition. Ocean Pictures éd., Moscow,
369 p.
Pezzotta, F., Guastoni, A., Diella, V. (2005): Scandium silicatesfrom the Baveno and Cuasso al Monte NYF-granites, Southern
Alps (Italy): mineralogy and genetic inferences. Am. Mineral,90, 1442–1452.
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112–122.
Vergasova, L.P., Semyonova, T.F., Epifanova, V.B., Filatov, S.K.,
Chubarov, V.M. (2004): Meniaylovite, Ca4AlSi(SO4)F13 12H2O,
a new mineral of volcanic exhalations. J. Volcanol. Seismol., 2, 3–5.
Vignola, P., Hatert, F., Medenbach, O., Bersani, D., Diella, V.,
Gentile, P., Risplendente, A. (2011): Chukhrovite-(Ca), IMA
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Vol. C. Kluwer Academic Press ed., London, 883 p.

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Received 29 February 2012
Modified version received 25 April 2012
Accepted 21 June 2012eschweizerbart_xxx