Eur. J. Mineral.
2003, 15, 181–184

Cavoite, CaV3O7, a new mineral from the Gambatesa mine,
northern Apennines, Italy
RICCARDO BASSO1*, GABRIELLA LUCCHETTI1, ALBERTO MARTINELLI2 and ANDREA PALENZONA2
1 Dipartimento per lo Studio del Territorio e delle sue Risorse, Università di Genova, Corso Europa 26,I-16132 Genova, Italy* Corresponding author, e-mail: mineral@dipteris.unige.it
2 Dipartimento di Chimica e Chimica Industriale, Università di Genova, Via Dodecaneso 31, I-16146 Genova, Italy
Abstract: Cavoite, CaV3O7, occurs at the Gambatesa mine (Liguria, Italy) filling microcavities in massive bands of caryopilite +calcian rhodochrosite quartz. Cavoite has been found as very rare radiated aggregates of strongly elongated prismatic to acicular
crystals up to about 0.28 mm in length, closely associated with an unidentified silicate phase. The crystals vary in colour fromcolourless to olive green-brown; they are brittle, transparent and non-fluorescent, with vitreous lustre and near white streak; nocleavage, parting or twinning were observed. The mean empirical formula from microprobe analyses, based on seven oxygen atoms,is (Ca0.95 Mn0.03K0.02)(V2.79Si0.22)O7. It well approaches the ideal one, CaV3O7, taking into account that the chemical determinations(presence of K, Mn and Si) are possibly affected by contamination due to the close association with the unidentified silicate. The
powder-diffraction data give the refined cell parameters a = 10.42(2) A, b = 5.28(2) A, c = 10.34(2) A and V = 568.2 A3 in the spacegroup Pnam. Micrometric crystals of cavoite were also investigated by means of transmission and analytical electron microscopy.
Cavoite is the natural analogue of the synthetic CaV3O7, whose structural study is reported in literature together with that of theisostructural phases SrV3O7 and CdV3O7.
Key-words: cavoite, new mineral, physical and chemical data, X-ray powder pattern, TEM analysis.

Introduction

Occurrence and physical properties

In the manganiferous ores of the Val Graveglia, northern
Apennines, Italy, a complex network of veins and fractures
allowed the formation of a great variety of rare and newminerals; among these, vanadium minerals, as saneroite,medaite, palenzonaite, gamagarite, volborthite, tangeite,reppiaite, and vanadomalayaite (Basso et al., 1994 and references therein), are frequent. In this paper we report a new
vanadium mineral species found at the Gambatesa mine,near the village of Reppia.
Because of the scarcity of material, specimens of the newmineral suitable to obtain experimental data about e.g. hardness, density, optical properties and crystal structure were
not found.
Both the mineral and the name, derived from the chemical composition, have been approved by the I.M.A. Commission on New Minerals and Mineral Names (ref. 2001–024). Type material is deposited in the collection of the Dipartimento per lo Studio del Territorio e delle sue Risorse(Dip.Te.Ris), Università di Genova, Italy.

In Eastern Liguria, manganese ores occur near the bottom ofchert sequences (“Diaspri di Monte Alpe” Formation) overlaying Jurassic ophiolites and consist of braunite-bearing
layers within hematite-rich cherts. A general overview ofthese Mn-ores is presented in Cabella et al. (1998).
Tectono-metamorphic re-equilibration under prehnitepumpellyite facies conditions (T = 275 25 °C; P = 2.5
0.5 kbar; Cortesogno et al., 1979; Lucchetti et al., 1990) affected ophiolites and their sedimentary covers; sedimentary
Mn-oxides and hydroxides equilibrated to braunite-dominated assemblages. A complex vein and fracture system developed, mainly localized at the fold hinges, inducing reaction processes responsible for the formation of Mn-silicate
and/or Mn-carbonate assemblages at the expense of braunite + quartz assemblages.
Fluids circulating along later fractures, at decreasing
metamorphic conditions, led to the concentration of elements such as V, As, Ba, Sr and the precipitation of a great
variety of uncommon minerals.
Cavoite occurs filling microcavities in massive bands ofcaryopilite + calcian rhodochrosite
quartz. The assemblages developed, replacing tephroite + rhodonite veins,
within the braunite layers. The alteration of tephroite + rho-DOI: 10.1127/0935-1221/2003/0015-0181

0935-1221/03/0015-0181 $ 1.80
2003 E. Schweizerbart’sche Verlagsbuchhandlung, D-70176 Stuttgart

182

R. Basso, G. Lucchetti, A. Martinelli. A. Palenzonadonite to caryopilite and carbonates assemblages is referredto the increased activity of CO2-bearing and Ca-rich hydrous fluids in the veins, which also induced V mobilization.
Cavoite has been found as very rare radiated aggregatesof strongly elongated prismatic to acicular crystals up toabout 0.28 mm in length. Only very few acicular crystals
show a composition near to CaV3O7 and they are closely associated with an unidentified silicate phase. The crystals
vary in colour from colourless to olive green-brown; theyare brittle, transparent and non-fluorescent, with vitreous
lustre and near white streak; no cleavage, parting or twinning were observed.
Due to the unusual scarcity of available material and to
the reduced sizes of the needle-like crystals (up to 2 µm in
width as measured by electron microscope) hardness anddensity could not be measured. The density, 3.51 g/cm3, iscalculated from empirical formula. Concerning the optical
data a value of about 2 was roughly measured for a refractive index, but the accuracy of the evaluation is low due tothe interference of the associated phase.

Chemical compositionTen spot chemical analyses were carried out on two distinct
crystals by means of an electron microprobe (PHILIPSSEM 515 electron microscope equipped with EDAXPV9100 spectrometer) in energy-dispersion mode, with anaccelerating voltage of 15 kV and a beam current of about 2nA. Clinopyroxene (Ca), fayalite (Mn, Si), amphibole (K),and metallic vanadium (V) were used as reference standards
for the elements in brackets. Other elements, if present,
were below their detection limits.
The mean chemical composition is reported in Table 1,along with an indication of variability and the most SiO2poor analyses. The mean empirical formula, based on seven
oxygen atoms, is (Ca0.95 Mn0.03K0.02) (V2.79Si0.22) O7. It wellapproaches the ideal one, CaV3O7, taking into account thatthe chemical determinations (presence of K, Mn and Si) are
possibly affected by contamination due to the close association with the unidentified silicate. This contamination isprobably responsible also for the colour variation from olive
green-brown, peculiar to CaV3O7, to nearly colourless.
The unidentified silicate chemical composition varies in
the ranges (wt%): MgO 3.78 – 6.33, K2O 1.67 – 2.94, CaO
0.53 – 1.91, MnO 2.45 – 3.50, VO2 21.93 – 24.17 and SiO2
41.24 – 49.97 (total from 73 to 85), but a possible misunder-standing on these data may be expected related to an unknown degree of contamination of the analyzed silicate
crystals by cavoite.

X-ray powder-diffraction analysis
The X-ray powder-diffraction analysis was performed by aGandolfi camera (diameter 57.3 mm) using a V filtered
CrK radiation and with silicon as internal standard. Relative intensities were assigned visually and the reflections
were indexed in the non-standard space group Pnam (n. 62)
on the basis of the pattern reported for the synthetic CaV3O7(Bouloux & Galy, 1973).
The measured powder data, reported together with thoseof the synthetic CaV3O7 in Table 2, give the refined cell parameters: a = 10.42(2) A, b = 5.28(2) A, c = 10.34(2) A and
V = 568.2 A3.

TEM analysis
Material from the holotype sample was analyzed with a JEOL JEM-2010 transmission electron microscope (TEM) operated at 200 kV. The analytical electron microscope (AEM)
investigations were performed using an energy-dispersive
X-ray spectrometer (EDS) system (OXFORD PENTAFET). Selected area electron diffraction (SAED) patterns
and AEM data were used for the mineral characterization.
The specimens for TEM examination were prepared startingfrom selected grains, crushed by means of a micro-tool(tweezer) and deposited onto a Cu support grid coated witha holey carbon film. The EDS analyses revealed for somecrystals a composition very near to Ca = 25 %at and V = 75%at, in agreement with the cationic ratio of CaV3O7. Tracesof Si are present and probably due to impurities. Other ele-Table 2. Comparison between powder-diffractiondata of cavoite (present study) and synthetic CaV3O7 (Bouloux & Galy, 1973) (d in A).
hkl

Oxide

Mean (wt%)

Range (wt%)

Most SiO2-poor (wt%)

CaO
MnO
K2 O
VO 2
SiO 2

17.76
0.70
0.35
76.80
4.31

15.90– 18.35
0.30– 0.82
0.20– 0.78
75.62– 82.02
0.92– 6.86

15.90
0.32
0.20
82.02
0.92

17.02
0.67
0.39
79.77
2.06

18.35
0.74
0.28
77.98
2.75Total

99.92

99.36

99.91

100.10synthetic
dhkl

200

5.16

M

5.25015

202
211

3.60

VVW

3.69

205024

3.45

W

3.50

3.00

S

3.023

124
414

2.902006

2.886
2.651
2.614
2.593
2.085

112212

Table 1. Chemical composition of cavoite.

cavoite
dI

013
2.88

synthetic
d

1.93

VW

1.930

1.85

M

1.854

1.82

VW

1.824

1.73

VW

1.740

602
405

1.65
1.62

VW
VW

1.651
1.625

612
033
216

1.56

W

1.575

W

203020400004403

cavoite
dI

2.63

VW

2.59
2.07

VVWVWCavoite

183[110] zone axes, respectively. It should be pointed out thatthe [110] pattern shows some kinematically forbidden reflections. For example, the 001 reflection should be absent
because in the space group Pnam the reflection condition forthe (00l) planes is l = 2n. Anyway dynamical scattering
events may occur and, for example, the allowed 110 diffracted beam may be rediffracted by the (111) planes giving
the reflection 001.
From the AEM and SAED analysis it may be inferred thatthe examined crystals are characterized by the same compositional and structural features reported for synthetic
CaV3O7.
Unfortunately TEM analysis does not improve the very
poor data relative to the unidentified silicate phase. This
mineral appears as parallel aggregates of acicular polycrystalline individuals, less than 0.4 µm in diameter. It shows
diffraction effects of very poor quality and the EDS analyses, probably affected by contamination due to the associated cavoite, give compositions running in the ranges of oxide
percents above reported.

Relationships to other minerals
Fig. 1. TEM image of a cavoite crystal (large and black) together
with some crystals of the associated unidentifiedsilicate phase (lightand dark grey).

ments, if present, are below their detection limits. SAED
patterns for these crystals, indexed in the space group Pnam,
lead to values of cell edges within the ranges a = 10.40 –10.43 A, b = 5.25 – 5.28 A and c = 10.33 – 10.37 A, in agreement with the ones refined from powder data. A TEM imageof a micrometric crystal of cavoite (large and dark), whose
EDS analysis gives a composition very near to the ideal one,is shown in Fig. 1 together with some crystals of the associated unidentified silicate phase.
The crystals of cavoite provide electron diffraction patterns consistent with the structure of synthetic CaV3O7:
Fig. 2 shows two SAED patterns viewed down [213] andFig. 2. SAED patterns collectedon cavoite crystals viewed
down [213] (left) and [110](right).

Cavoite is the natural analogue of the synthetic CaV3O7,
whose structural study is reported in Bouloux & Galy
(1973) together with those of the isostructural phases
SrV3O7 and CdV3O7. The CaV3O7 structure may be described as built up by corrugated layers of edge-sharing[V4+O5] square pyramids linked by Ca atoms. Other minerals involving V4+ with square pyramidal coordination polyhedron are known and their structures are characterized bylower degrees of condensation of the [VO5] pyramids thancavoite. The condensation takes place in all the cases bysharing edges and with the apical oxygens of adjacentpyramids pointing to opposite sides. In haradaite,
Sr2V2O2(Si4O12) (Takéuchi & Joswig, 1967), and in its Ba
analogue suzukiite (Matsubara et al., 1982) as well as in thetwo dimorphs cavansite and pentagonite, Ca(VO)(Si4O10)·
4H2O (Evans, 1973), the [VO5] pyramids are isolated. Double pyramids [V2O8] share corners with [V5+O4] tetrahedra
in the bronze melanovanadite, CaV4O10·5H2O (Konnert &184

R. Basso, G. Lucchetti, A. Martinelli. A. Palenzona

Evans, 1987). Finally, the condensation increases to chainsin the Sb2VO5 polytypes stibivanite-2M (Kaiman et al.,1980) and -2O (Merlino et al., 1989).
Acknowledgements: This study was supported by the Ministero dell’Università e della Ricerca Scientifica e Tecnologica: projects “Crystal chemistry of mineral species: useof advanced techniques for a modern systematics” and“Crystal chemistry of ore minerals and their alterations”.

References
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Bouloux, J.C. & Galy, J. (1973): Les Hypovanadates MV3O7(M=Ca, Sr, Cd). Strutture Cristalline de CaV3O7. Acta Cryst.,
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Cortesogno, L., Lucchetti, G., Penco, A.M. (1979): Le mineralizzazioni a manganese nei diaspri delle ofioliti liguri: mineralogia egenesi. Rend. S.I.M.P., 35, 151–197.

Evans, H. T. Jr. (1973): The crystal structuresof cavansite and pentagonite. Amer. Miner., 58, 412–424.
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Received 30 May 2002
Modified version received 4 September 2002
Accepted 21 October 2002