Mineralogical Magazine, October 2011, Vol. 75(5), pp. 2677–2686

Bassoite, SrV3O7˝4H2O, a new mineral from
Molinello mine, Val Graveglia, eastern Liguria, Italy
L. BINDI1,2, C. CARBONE3,*, R. CABELLA3 AND G. LUCCHETTI3
1

Museo di Storia Naturale, Sezione Mineralogia e Litologia, Università degli Studi di Firenze, Via G. La Pira 4, I50121 Firenze, Italy
2
CNR Istituto di Geoscienze e Georisorse, Sezione di Firenze, Via G. La Pira 4, I-50121 Firenze, Italy
3
Dipartimento per lo Studio del Territorio e delle sue Risorse, Università di Genova, Corso Europa 26, I-16132
Genova, Italy[Received 16 June 2011; Accepted 14 July 2011]

ABSTR ACT

Bassoite, ideally SrV3O7·4H2O, is a new mineral from the Molinello manganese mine, Val Graveglia,
eastern Liguria, northern Apennines, Italy. It occurs as black euhedral to subhedral grains up to 400 mm
across, closely associated with rhodonite, quartz and braunite. Bassoite is opaque with a sub-metallic
lustre and a black streak. It is brittle and neither fracture nor cleavage was observed; the Vickers microhardness (VHN100) is 150 kg/mm2 (range 142 165; corresponding to a Mohs hardness of 4 4@). The
calculated density is 2.940 g/cm3 (on the basis of the empirical formula and X-ray single-crystal data).
Bassoite is weakly bireflectant and very weakly pleochroic from grey to a dark green. Internalreflections are absent. The mineral is anisotropic, without characteristic rotation tints. Reflectancepercentages (Rmin and Rmax) for the four standard COM wavelengths are 18.5%, 19.0% (471.1 nm);17.2%, 17.8% (548.3 nm); 16.8%, 17.5% (586.6 nm) and 16.2%, 16.8% (652.3 nm), respectively.
Bassoite is monoclinic, space group P21/m, with unit-cell parameters: a = 5.313(3) Å, b = 10.495(3) Å,c = 8.568(4) Å, b = 91.14(5)º, V = 477.7(4) Å3, a:b:c = 0.506:1:0.816, and Z = 2. The crystal structure
was refined to R1 = 0.0209 for 1148 reflections with Fo > 4s(Fo) and it consists of layers of VO5pyramids (with vanadium in the tetravalent state) pointing up and down alternately with Sr between thelayers (in nine-fold coordination). The nine most intense X-ray powder-diffraction lines [d in Å (I/I0)(hkl)] are: 8.5663 (100) (001); 6.6363 (14) (011); 3.4399 (14) (1̄21); 3.4049 (17) (121); 2.8339 (15)(1̄22); 2.7949 (11) (122); 2.6550 (15) (200); 2.6237 (11) (040) and 1.8666 (15) (240). Electron
microprobe analyses produce a chemical formula (Sr0.97Ca0.02Na0.01)V3.00O7·4H2O, on the basis of
S(Sr+Ca+Na) = 1, taking the results of the structure refinement into account. The presence of watermolecules was confirmed by micro-Raman spectroscopy. The name honours Riccardo Basso (b. 1947),
full professor of Mineralogy and Crystallography at the University of Genova. The new mineral andmineral name have been approved by the Commission on New Minerals, Nomenclature andClassification, IMA (2011-028).

K EY WORDS : bassoite, new mineral, electron microprobe data, reﬂectance data, X-ray diffraction data,
Molinello mine, Val Graveglia, Liguria, Italy.

Introduction* E-mail: carbone@dipteris.unige.it
DOI: 10.1180/minmag.2011.075.5.2677# 2011 The Mineralogical Society

IN the Val Graveglia mines, Mn ores occur as
braunite-bearing layered massive lenses andboudins near the stratigraphic base of the chertsof the ‘Diaspri di M. Alpe’ Formation, which
overlies an ophiolitic basement (Cabella et al.,1998). Mineralization is characterized by a

L. BINDI ET AL.

braunite-quartz assemblage which equilibrated
under prehnite pumpellyite-facies conditions(Cortesogno et al., 1979; Lucchetti et al., 1990)
during a tectono-metamorphic event that affectedboth the ophiolite and chert. Hydrothermal ﬂuid
circulation along later extensional fractures, atlower-grade metamorphic conditions, concentrated
dispersed elements, such as As, Ba, Cu, Sr, and V,
and precipitated a variety of uncommon minerals.
Vanadium minerals such as saneroite, medaite,
palenzonaite, gamagarite, volborthite, tangeite,
reppiaite, and vanadomalayaite (Marchesini andPagano, 2001) are common in this assemblage.
Here we report the description and characterizationof a new V4+-bearing mineral from Val Graveglia,
eastern Liguria, northern Apennines, Italy. The
mineral, ideally SrV3O7·4H2O, is named after
Riccardo Basso (b. 1947), full professor ofmineralogy and crystallography at the Universityof Genova, Italy. Riccardo Basso has worked on
the characterization of several new V-rich minerals
from the Ligurian region and has determined the
crystal structure of most of them (Basso et al.,
1994, 2003, 2005). The new mineral and mineralname have been approved by the Commission on
New Minerals, Nomenclature and Classiﬁcation,
IMA (2011-028). Holotype material is deposited in
the mineralogical collection of the Dipartimento
per lo Studio del Territorio e delle sue Risorse,
Università di Genova, Italy, under catalogue
number M0480.

In plane-polarized incident light, bassoite is
weakly bireﬂectant and very weakly pleochroic
with colour varying from grey to dark green. Withcrossed polars, bassoite is anisotropic, without
characteristic rotation tints. Internal reﬂections areabsent and there is no evidence of growth zoning.
Reﬂectance measurements were performed in
air using a Zeiss MPM-200 microphotometerequipped with an MSP-20 system processor on a
Zeiss Axioplan ore microscope. The ﬁlament
temperature was approximately 3350 K. An
interference ﬁlter was used to select the four
wavelengths for measurement (471.1, 548.3,
586.6 and 652.3 nm). Measurements wereobtained from an area 0.1 mm in diameter forthe specimen and a SiC standard under the same
conditions. Reﬂectance percentages (Rmin andRmax) are 18.5%, 19.0% (471.1 nm); 17.2%,
17.8% (548.3 nm); 16.8%, 17.5% (586.6 nm) and16.2%, 16.8% (652.3 nm), respectively.
X-ray crystallography and crystal-structure
determination

Occurrence and physical properties
The sample containing the new mineral bassoite,
SrV3O7·4H2O, was collected at the Molinello
mine, Val Graveglia, eastern Liguria, northern
Apennines, Italy. The sample mainly consists ofbassoite with associated rhodonite, quartz andbraunite (Fig. 1). Bassoite occurs as euhedral tosubhedral grains which are homogeneous and notintergrown with other minerals. The maximum
grain size is about 400 mm.
Bassoite is black in colour and has a black
streak. It is opaque with a sub-metallic lustre andit is brittle without fracture or cleavage. The
density could not be determined experimentally
because of the small grain size. The calculated
density is 2.940 g/cm3 (on the basis of theempirical formula and X-ray single-crystal data).
The micro-indentation measurements, carried out
with a VHN load of 100 g, gave a mean value of
150 kg/mm2 (range: 142 165), corresponding toa Mohs hardness of 4 to 4@.
2678

Several crystals of bassoite were selected from thetype specimen (Fig. 1) and examined using a
Bruker MACH3 single-crystal diffractometer withgraphite-monochromated Mo-Ka radiation. The
unit-cell dimensions were determined by leastsquares reﬁnement of the setting angles of
25 high-y reﬂections (12º < yMo-Ka < 18º). This
procedure gave nearly identical unit-cell dimensions for all of the crystals that were investigated.
As the crystals produced nearly identical results,
we decided to collect data using the crystal that
produced the best quality diffraction data only.
The data was collected using an Oxford
Diffraction Xcalibur 3 diffractometer, ﬁtted with

FIG. 1. Black bassoite crystals on rhodonite.

BASSOITE, A NEW MINERAL FROM LIGURIAa Sapphire 2 CCD detector (see Table 1 fordetails). Intensity integration and standard
Lorentz-polarization corrections were performed
using the CrysAlis RED (Oxford Diffraction,2006) software package. The empirical absorption
correction was determined by the ABSPACK
program, which is also part of the CrysAlis RED
suite (Oxford Diffraction, 2006). The agreement
among equivalent reﬂections for the data set
expressed as Rint decreased from 0.1335 before
the absorption correction was applied to 0.0690
after correction. Statistical tests on the distribution
of |E| values (|E2 1| = 0.863), which indicated thepresence of an inversion centre, together with theobserved systematic absences, led unequivocallyto the choice of the space group P21/m.
The positions of most of the atoms (all of themetals and two O-positions) were determined fromthe three-dimensional Patterson synthesis(Sheldrick, 2008). A least-squares reﬁnement
using these heavy-atom positions and isotropic
temperature factors yielded an R factor of 0.1018.
Three-dimensional difference Fourier synthesis
yielded the positions of the remaining oxygen
atoms. The full-matrix least-squares program
SHELXL-97 (Sheldrick, 2008) was used for thereﬁnement of the structure. All atom sites were
found to be fully occupied. Neutral scattering
curves for Sr, V and O, taken from The
International Tables for X-ray Crystallography,
volume IV (Ibers and Hamilton, 1974) were used.
In the last stage of the analysis, with the anisotropic
atomic displacement parameters assigned to all
atoms and with no constraints, the residual value
settled at R1 = 0.0209 for 491 observed reﬂections[Fo > 4s(Fo)] and 77 parameters and at R1 = 0.0238

TABLE 1. Crystallographic data and reﬁnement parameters for bassoite.
Crystal data
Ideal formula
Crystal system
Space group
Unit-cell parameters a, b, c (Å)
b (º)
Unit-cell volume (Å3)
Z
Crystal size (mm)SrV3O7·4H2O
monoclinic
P21/m
5.313(3), 10.495(3), 8.568(4)91.14(5)477.7(4)20.02460.03160.039

Data collection
Diffractometer
Temperature (K)Radiation, wavelength (Å)
y range for data collection (º)
h, k, l ranges
Axis, frames, width (º), time per frame (s)Total reflections collected
Unique reflections (Rint)
Unique reflections Fo > 4s(Fo)Data completeness to ymax (%)
Absorption correction method

Oxford Diffraction Excalibur 3 (CCD)
298(3)Mo-Ka, 0.71073
3.15 - 29.46
W7, W13, W11o, 789, 0.60, 110
4592
1148 (0.069)
491
98.9
multiscan (ABSPACK)

Structure refinement
Refinement method
Weighting scheme
Data/restraints/parameters
R1 [F > 4s(F)]R1 allLargest difference, peak and hole (e /Å3)

Full-matrix least-squares on F2
1/s2(F)
1148/0/77
0.02090.02380.52, 0.82

Rint = (n/n 1)1/2[F2o Fo (mean)2]/SF2o
R1 = S||Fo| |Fc||/S|Fo|
Where n is the number of reﬂections and p is the number of reﬁned parameters.

2679

L. BINDI ET AL.

TABLE 2. Atoms, multiplicity and Wyckoff position, fractional atom coordinates (Å), and equivalent isotropic
displacement parameters (Å2) for bassoite.
Atom

Wyckoff

x

y

z

Uiso

Sr
V1
V2
O1
O2
O3
O4
O5W
O6W
O7W

2e
2e
4f
4f
4f
4f
2e
4f
2e
2e

0.25846(9)0.74697(16)0.24763(11)0.0100(4)0.5171(4)0.7670(4)0.7379(5)0.2615(4)0.2058(8)0.7461(7)[[0.01931(6)0.1155(2)0.1169(2)0.0478(2)[0.0169(2)[[0.23638(7)0.04422(11)0.07309(7)0.0288(3)0.0315(3)0.2567(2)0.7720(4)0.3526(3)0.5372(6)0.3506(5)0.0372(2)0.0309(3)0.0268(2)0.0290(8)0.0296(8)0.0255(8)0.0268(12)0.0388(9)0.085(2)0.0737(19)for all 1148 independent reﬂections. Inspection of
the difference Fourier map revealed that maximum
positive and negative peaks were 0.52 and 0.82
e /Å3, respectively. Experimental details and R
indices are given in Table 1. Fractional atom
coordinates and anisotropic-displacement parameters are provided in Tables 2 and 3, respectively.
Bond distances are reported in Table 4. The
calculated X-ray powder pattern for bassoite
computed with XPOW (Downs et al., 1993) using
the atomic coordinates and the occupancy factors
reported in Table 2 is reported in Table 5. Structure
factors are deposited with the Principal Editor of
Mineralogical Magazine at http://www.minersoc.
org/pages/e_journals/dep_mat.html.
Chemical composition
A preliminary chemical analysis using energydispersive spectrometry (EDS), on the crystal
fragment used for the structural study, did notindicate the presence of elements (Z > 9) otherthan Sr, V, O and very minor Ca and Na (Fig. 2).
The chemical composition was determined bywavelength-dispersive spectrometry (WDS) using
a JEOL JXA-8200 electron microprobe on thesame crystal fragment used for the structural
study. Major and minor elements were determinedat 15 kV accelerating voltage and 30 nA beam
current, with 20 s as counting time and a 1 mmbeam diameter. For the WDS analyses, Sr-Ka,
Ca-Ka, Na-Ka and V-Ka lines were used. The
crystal fragment was found to be homogeneous
within analytical uncertainty (7 analyses on
different spots). The H2O content was calculated
by stoichiometry from the results of the crystalstructure analysis; its presence was conﬁrmed by
Raman spectroscopy (see below). Analytical data
are presented in Table 6.
On the basis of (Sr + Ca + Na) = 1, the formulaof bassoite is (Sr0.97Ca0.02Na0.01)V3.00O7·4H2O.
The simpliﬁed formula is SrV3O7·4H2O, which

TABLE 3. Anisotropic displacement parameters of the atoms in bassoite.
Atom

U11

U22

U33

U12

U13

U23

Sr
V1
V2
O1
O2
O3
O4
O5W
O6W
O7W

0.0370(3)0.0311(5)0.0267(3)0.0289(13)0.0298(13)0.0266(13)0.0282(18)0.0395(15)0.073(3)0.076(3)0.0375(3)0.0314(6)0.0277(4)0.0294(15)0.0299(15)0.0271(13)0.028(2)0.0442(16)0.068(3)0.078(3)0.0370(4)0.0303(6)0.0261(4)0.0286(16)0.0289(16)0.0229(15)0.024(2)0.0326(17)0.113(5)0.067(4)000.0003(3)0.0024(12)0.0006(12)0.0011(11)00.0012(14)000.0005(3)0.0010(4)0.0010(3)0.0018(11)0.0009(11)0.0018(10)0.0012(15)0.0004(12)0.002(3)0.002(3)000.0001(3)0.0014(11)0.0001(11)0.0013(11)00.0013(13)
0
0

2680

BASSOITE, A NEW MINERAL FROM LIGURIATABLE 4. Interatomic distances (Å) for bassoite.
Sr
Sr
Sr
Sr
Sr
Sr
Sr
Sr
Sr

O1
O1i
O2
O2i
O5
O5i
O6
O7ii
O7

2.663(2)2.663(2)2.649(2)2.649(2)2.641(2)2.641(2)2.598(5)2.911(4)2.751(4)

V1
V1
V1
V1
V1
V1
V1

O1v
O1vi
O2
O2i
O4vii
V2iii
V2iv

2.004(2)2.004(2)1.974(2)1.974(2)1.575(3)2.9997(7)2.9997(7)

V2
V2
V2
V2
V2
V2
V2

O1
O1viii
O2
O2iii
O3iii
V2viii
V2iii

1.924(2)1.939(2)1.962(2)1.928(2)1.601(2)2.9643(8)2.9648(8)requires SrO 24.41, VO2 58.61, H2O 16.98, total
100.00 wt.%.

O1
O1
O1
O1
O1
O1
O1

O1viii
O1i
O2ii
O2
O3ii
O3iii
O4ix

2.477(3)2.823(3)2.513(3)2.800(3)2.871(3)2.877(3)2.917(3)

O2
O2
O2
O2
O2

O2iii
O2i
O3
O3iii
O4vii

2.518(3)2.794(3)2.893(3)2.958(3)2.894(4)

O3 O5
O3 O5vO3 O6x2.905(3)2.820(3)2.763(4)O4 O5xO4 O5xi

2.998(3)2.998(3)O5 O6

2.931(4)O6 O7ii

2.892(6)Raman investigation
Raman spectra were collected using a Renishaw
RM2000 micro-Raman apparatus, coupled with adiode laser source emitting at 785 nm. The sample
was irradiated using the 506 microscope objective
on a Leica DMLM microscope. The beam power
was ~3 mW and the laser spot size was adjusted to
between 1 and 3 mm. The Raman data werecollected by an air-cooled CCD detector. The
acquisition time for each measurement was 20 s.
All spectra were calibrated with respect to a siliconwafer at 520 cm 1. Unpolarized spectra in theregion 1250 2000 cm 1 and 3000 4000 cm 1
are shown in Fig. 3. The peak at 1645 cm 1 inFig. 3a is ascribed to H2O bending whereas thepeaks at 3407 and 3534 cm 1 in Fig. 3b are
produced by OH stretching.
Description of the structure and discussion

Symmetry codes are: (i) x,1/2 y,z; (ii) 1+x,y,z;(iii) 1 x, y, z; (iv) 1 x,1/2+y, z; (v) 1+x,y,z;(vi) 1+x,1/2 y,z; (vii) x,y, 1+z; (viii) x, y, z;(ix) 1+x,y, 1+z; (x) 1 x, y,1 z; (xi) 1 x,1/2+y,1 z.

The crystal structure of bassoite (Fig. 4) consistsof layers parallel to {001} consisting of edgesharing V4+O5 square pyramids, with the Sr
between the layers in nine-fold coordination.
The VO5 pyramids are the basic structural units
in bassoite. There are two distinct vanadium
positions, V1 and V2. The V2O5 pyramids, withapices pointing up and down alternately, form

FIG. 2. Elemental X-ray maps of bassoite (B) with rhodonite (R). The red colour refers to vanadium whereas the blueand green colours refer to Mn and Si, respectively.

2681

L. BINDI ET AL.

TABLE 5. Calculated X-ray powder diffraction data for bassoite.
Icalc

dcalc

h

k

l

Icalc

dcalc

h k

l

100.00
14.08
2.59
1.42
1.76
2.87
2.05
3.34
13.89
17.37
4.07
5.08
6.15
5.44
1.27
3.45
15.10
11.48
2.01
2.00
3.10
14.81
11.33
2.99
2.57
1.65
1.47
1.95
1.70
1.08
1.26
1.14
3.56
1.82

8.5663
6.63634.73954.55524.47474.47474.1786
4.11623.43993.40493.31823.2387
3.20623.15012.92172.85542.83392.79492.77452.75602.75532.65602.62372.53622.49452.46532.42692.42602.40142.27362.26342.23732.21212.1416

0
0
1
1
1
0
1
1
1
1
0
0
1
1
1
0
1
1
1
1
0
2
0
1
1
1
1
1
1
1
1
0
0
0

0
1
1
0
0
2
1
1
2
2
2
3
1
1
3
0
2
2
3
3
1
0
4
0
0
1
1
3
3
4
4
4
3
0

1
1
0
1
1
1
1
1
1
1
2
1
2
2
0
3
2
2
1
1
3
0
0
3
3
3
3
2
2
1
1
2
3
4

1.52
1.42
2.20
1.32
2.63
2.14
2.35
2.10
14.96
1.10
3.25
2.10
1.87
1.77
1.76
1.05
1.84
1.06
1.46
2.06
3.92
1.26
3.94
1.92
1.06
1.23
1.27
1.03

2.06132.05342.04622.03101.98281.95211.93081.89411.8666
1.84651.82911.82351.81851.80781.69121.65231.64061.6031
1.57501.5722
1.5654
1.5522
1.54891.32801.31191.2102
1.1876
1.1849

2
1
2
1
0
1
2
2
2
1
2
1
2
1
0
3
3
2
2
3
1
1
1
4
0
3
3
4

1
3
1
3
4
0
3
3
0
4
1
3
1
3
3
1
1
4
4
2
5
2
5
0
0
5
5
0

3
3
3
3
2
5
1
1
4
2
4
4
4
4
5
2
2
2
2
2
2
6
2
0
8
2
2
4

The calculated X-ray powder pattern was computedon the basis of a = 5.313(3) Å, b = 10.495(3) Å,c = 8.568(4) Å, b = 91.14(5)º, and with the atomic
coordinates reported in Table 2.

TABLE 6. Electron microprobe data for bassoite.
Constituent

Wt.%

SrO
CaO
Na2O
VO2
H2O*
Total

23.66
0.27
0.07
58.56
16.99
99.55

Range
23.40
0.20
0.05
58.01

23.81
0.31
0.14
58.71

* from crystal structure stoichiometry.

2682

Stand. Dev.

Probe standard

0.15
0.04
0.02
0.19

Strontianite
CalciteAlbiteVanadium metal

BASSOITE, A NEW MINERAL FROM LIGURIA

FIG. 3. Unpolarized micro-Raman spectra of bassoite in: (a) the 1250 2000 cm 1 region and (b) the 3000 4000 cm 1
region.

inﬁnite edge-sharing ribbons parallel to [100],
whereas the V1O5 pyramids link these chains byedge-sharing parallel to [010] (Fig. 5). The meanbond distances for the VO5 pyramids (1.906 and1.871 Å for V1 and V2, respectively) is inexcellent agreement with those observed insynthetic AV3O7 (A = Ca, Sr) V4+-oxovanadates(Prinz et al., 2007). The slight difference in thesize of the two VO5 pyramids is related to the factthat whereas V1 shares only two edges, V2 shares
three edges of the base. As a consequence, the V2
pyramid has a smaller base area and a longer
apical distance.
The Sr2+ cations are located between the layers
and are coordinated by nine O atoms. There areseven shorter distances (from 2.598 Å to 2.663 Å)

FIG. 4. A projection of the bassoite structure along [100] (slightly canted). The Sr atoms are shown as light blue
spheres, O atoms of VO5 pyramids as small red spheres and O atoms of water molecules as light orange spheres. The
V1O5 and V2O5 pyramids are green and blue, respectively. The unit cell is outlined.

2683

L. BINDI ET AL.

FIG. 5. A projection of a portion of the bassoite structure along [001] to show the topology of the V3O7 layer. The Sr
atoms are shown as light blue spheres, O atoms of VO5 pyramids as small red spheres. The V1O5 and V2O5
pyramids are green and blue, respectively. The unit cell is outlined.

and two longer ones (2.751 Å and 2.911 Å;Table 4). This Sr coordination is quite different
from that observed in the orthorhombic crystal
structure of anhydrous SrV3O7 (Prinz et al.,2007), where the Sr O distances can begrouped into three distance ranges: two rather
long Sr O1 distances of 2.975 Å, two short
Sr O2 distances of 2.483 Å and four equivalentintermediate Sr O3 distances of 2.565 Å.
An interesting structural feature is observed if
we consider the tilt angle (d) between the basal
planes of the V1O5 and V2O5 pyramids (Fig. 6).
This parameter was ﬁrst introduced by Bouloux
and Galy (1973) in their study of V4+-bearing
oxovanadates. The tilt angle gives an usefulestimation of the degree of buckling of theV3O7 layers. In comparing the room-temperature
crystal structures of CaV3O7 and SrV3O7, Prinz etal. (2007) noticed a difference in the tilt angles[12.89(9)º and 9.3(2)º, respectively], and attributed it to the different sizes of the two alkalineearth cations. Indeed, as already postulated by
Bouloux and Galy (1973), the larger size of theSr2+ cation leads to a less pronounced buckling of
the V3O7 layers as compared with that in the Cacompound. The measured tilt angle d of 10.0(3)ºin bassoite is relatively small, which is in good
agreement with the ﬁndings of the earlier workers.
Although hydrogen atoms were not located in
the difference Fourier maps, bond-valence calculations (Table 7) clearly indicate that the oxygen
atoms O5, O6 and O7 belong to water molecules.
The presence of H2O was also conﬁrmed by
Raman spectroscopy (see above). To study apossible hydrogen-bonding system for the

bassoite structure, the O...O distances suitablefor hydrogen bonds were examined. There are
only four independent O...O contacts which are
not polyhedral edges. They are the following:d [O5 v ...O3] = 2 .820(3) Å ; d [O 5. ..O 3]= 2.905(3) Å; d[O5x,xii...O4] = 2.998(3) Å andd[O6x...O3] = 2.763(4) Å. As O5, O6 and O7
belong to water molecules, it seems likely that O3
acts as an acceptor of hydrogen bonds from both

FIG. 6. A portion of the bassoite structure along [100] toshow the tilt angle (d) between the basal planes of theV1O5 and V2O5 pyramids of the V3O7 layer (see text).
The Sr atoms are shown as light blue spheres, O atomsof VO5 pyramids as small red spheres and O atoms ofwater molecules as light orange spheres. The V1O5 andV2O5 pyramids are green and blue, respectively.

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BASSOITE, A NEW MINERAL FROM LIGURIATABLE 7. Bond-valence (v.u.) arrangement for bassoite.
SO

Sr

V1

V2

O1

0.22962;61?

0.5562;61?

0.658;61? 0.685;61?

O2

62 61?

62 61?

0.238

;

0.59

;

0.618;

O3

0.678;

1.640;

61?

1.759;61?

O4
O5

0.243

O6
O7

61?

61?

2.121
2.132
1.640
1.759

62 61?

;

0.243

61?

0.273

0.273;

0.117;61? 0.181;61?
1.991

0.298
4.059

4.279

Note: calculated from the bond-valence curves of Brese and O’Keeffe (1991).

O5 and O6 whereas O4 acts as an acceptor ofhydrogen bonds from two O5 atoms. Thus, thefollowing hydrogen-bonding model can beassumed: O5 ? O3, O6 ? O3, and O5 ? O4.
The situation is much more complicated for O7
where the O...O distance is longer and not to apolyhedral edge (i.e. d[O7...O3] = 3.213(3) Å).
Considering the proposed hydrogen-bonding
system and by adding the contributions of the Hatoms to donor and acceptor oxygens, satisfactory
oxygen bond-valence sums can be obtained.
However, a more detailed analysis of thehydrogen-bonding system in bassoite must await
the availability of either more suitable crystals or
the application of different, non-conventional
techniques.
Acknowledgements
We thank Alessandro Pozzi, a local mineralcollector, who provided the studied sample andDonato Belmonte for helpful discussions. The
manuscript beneﬁted from the revisions of
Fernando Cámara, Anthony Kampf, Jakub Plášil
and the Associate Editor Stuart Mills.
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