1423
The Canadian Mineralogist
Vol. 41, pp. 1423-1431 (2003)

ANSERMETITE, MnV2O6•4H2O, A NEW MINERAL SPECIES WITH V5+
IN FIVE-FOLD COORDINATION FROM VAL FERRERA, EASTERN SWISS ALPSJOËL BRUGGER§
School of Earth and Environmental Sciences, The University of Adelaide, North Terrace, 5005 Adelaide, South Australia,
and Division of Mineralogy, South Australian Museum, North Terrace, Adelaide 5000, South Australia, Australia

PETER BERLEPSCH
Laboratorium für Chemische und Mineralogische Kristallographie, Universität Bern,
Freiestrasse 3, CH-3012 Bern, Switzerland

NICOLAS MEISSER
Musée Géologique Cantonal UNIL–BFSH2, CH–1015 Lausanne-Dorigny, Switzerland, and Laboratoire des Rayons-X,
Institut de Minéralogie et de Géochimie, UNIL–BFSH2, CH-1015 Lausanne-Dorigny, Switzerland

THOMAS ARMBRUSTER
Laboratorium für Chemische und Mineralogische Kristallographie, Universität Bern,
Freiestrasse 3, CH-3012 Bern, Switzerland

ABSTRACT
Ansermetite, MnV2O6•4H2O, is a new mineral species from the metamorphosed synsedimentary exhalative Mn deposit ofFianel, Val Ferrera, Eastern Swiss Alps. The crystals are carmine red, transparent, with an orange streak and adamantine luster.
The Mohs hardness is ~3, Dcalc = 2.49 g/cm3, Dmeas = 2.57(2) g/cm3. Ansermetite has an excellent cleavage along {110}, theprism, and an uneven fracture. It is biaxial with nmin = 1.797 and nmax = 1.856 (NaD, 22.5°C), strongly pleochroic between yellow
orange (X) and ruby red (Z), and non-fluorescent. Chemically, ansermetite is near the end-member composition MnV2O6•4H2O,
containing only small amounts of arsenic (0.93 wt% As2O5) and strontium (0.20 wt% SrO). Ansermetite is monoclinic, C2/c, a
13.171(2), b 10.128(1), c 6.983(1) Å,  111.572(2)°, V 866.3(2) Å3, Z = 4. The crystal structure was solved with direct methods
on the basis of 701 reflections with I > 2(I) and refined to R1 = 7.01%. The structure is isotypic with that of synthetic
CoV2O6•4H2O and MnV2O6•4H2O. It contains V5+ in distorted square pyramidal coordination with five atoms of oxygen, and
Mn2+ in octahedral coordination with four atoms of oxygen and two H2O groups. The VO5 polyhedra share edges to form chains
extending along [001], and linked by MnO4(H2O)2 octahedra. This arrangement results in a three-dimensional framework defining tunnels that host the two H2O groups per formula unit belonging to MnO4(H2O)2 octahedra as well and two additional free
H2O groups. Ansermetite forms crystalline crusts up to ~500 m in thickness and several square centimeters in surface filling thinopen fractures cross-cutting V-rich Mn–Fe silicate–oxide ores. Ansermetite is associated to fianelite, Mn2V(V,As)O7•2H2O, Fe
oxyhydroxides and silica. Ansermetite and fianelite represent the latest stage of V mobility at the Fianel deposit. Ansermetite isstable at ambient conditions, but is unstable in air and aqueous solutions at temperatures above ~50 to 85°C. Ansermetite is likely
to have crystallized from near neutral to mildly acidic groundwater during the Quaternary.
Keywords: ansermetite, new mineral species, crystal structure, metavanadate, Starlera mine, Val Ferrera, Eastern Swiss Alps.

SOMMAIRE
L’ansermetite, MnV2O6•4H2O, nouvelle espèce minérale, a été découverte dans le gisement de manganèse synsédimentaire
exhalatif et métamorphisé de Fianel, Val Ferrera, Alpes orientales, en Suisse. Les cristaux sont rouge carmin et transparents, avec
un trait orange et un éclat adamantin. La dureté de Mohs est environ 3, Dcalc = 2.49, Dmes = 2.57(2) g/cm3. L’ansermetite possède
un excellent clivage le long de {110}, le prisme, et une fracture inégale. C’est un minéral biaxe avec nmin = 1.797 et nmax = 1.856(NaD, 22.5°C), fortement pléochroïque allant du jaune orange (X) à rouge rubis (Z), et non-fluorescent. Sa composition s’approche§

E-mail address: joel.brugger@adelaide.edu.au

1424

THE CANADIAN MINERALOGISTde celle du pôle, MnV2O6•4H2O, et contient un peu d’arsenic (0.93% As2O5, poids) et de strontium (0.20% SrO). Elle est
monoclinique, C2/c, a 13.171(2), b 10.128(1), c 6.983(1) Å,  111.572(2)°, V 866.3(2) Å3, Z = 4. Nous en avons résolu la
structure cristalline par méthodes directes en utilisant 701 réflexions ayant I > 2(I), et nous l’avons affiné jusqu’à un résidu R1
de 7.01%. La structure est isotypique de celle des composés synthétiques CoV2O6•4H2O et MnV2O6•4H2O. Elle contient V5+
avec un agencement de cinq atomes d’oxygène en pyramide carrée difforme, et le Mn2+ en coordinence octaédrique avec quatre
atomes d’oxygène et deux groupes de H2O. Les polyèdres VO5 partagent des arêtes pour former des chaînes le long de [001], etelles sont interliées au moyen d’octaèdres MnO4(H2O)2. Cet agencement mène à une trame tri-dimensionnelle avec des tunnels,
où logent les deux groupes de H2O par unité formulaire contribués par les octaèdres MnO4(H2O)2 ainsi que deux groupes de H2O
additionnels. L’ansermetite se présente en croûtes cristallines atteignant une épaisseur de ~500 m et plusieurs centimètres carréstapissant de minces fentes ouvertes recoupant le minerai vanadifère à silicate et oxydes de Mn–Fe. Elle est associée à la fianelite,
Mn2V(V,As)O7•2H2O, des oxyhydroxydes de fer et de la silice. L’ansermetite et la fianelite représentent le stade ultime demobilisation de vanadium dans ce gisement. L’ansermetite est stable aux conditions ambiantes, mais est instable dans l’air et dansdes solutions aqueuses à une température supérieure à l’intervalle ~50 à 85°C. Elle a probablement cristallisé à partir de l’eau
phréatique neutre ou légèrement acide au cours du Quaternaire.
(Traduit par la Rédaction)
Mots-clés: ansermetite, nouvelle espèce minérale, structure cristalline, métavanadate, mine Starlera, Val Ferrera, Alpes orientales,
Suisse.

INTRODUCTION
Metamorphosed Mn-rich deposits, such as atLångban in Sweden, the Kombat mine in Namibia, andat Franklin, New Jersey, U.S.A., are among the richestmineralogical “rain forests” on Earth (Pring 1995), andare still contributing a steady stream of new mineral
species. Many of these minerals contain arsenic or vanadium as a major component. In this paper, we describe
the occurrence and mineralogy of a new manganese
vanadate, occurring in the small metamorphosed Mn–
Fe deposit of Fianel, Canton Graubünden, Switzerland.
The mineral has been named ansermetite to acknowledge Stefan Ansermet’s (b. 1964) contribution to thedescriptive mineralogy and to the photography of the
Alpine mineralogical wealth. As an autodidact mineralogist and assistant at the Musée Cantonal Géologique(Lausanne, Switzerland) and at the Musée Cantonald’Histoire Naturelle (Sion, Switzerland), Stefan
Ansermet has published a number of papers in amateur
mineralogical journals, has coauthored several abstracts
in international mineralogical conferences (Meisser &Ansermet 1996, Brugger & Ansermet 2000), and has
recently published the first volume of a series of richly
illustrated books about the mines and minerals of the
Canton Valais (Ansermet 2001). The new mineral andits name have been approved by the International Mineralogical Association (proposal number 2002–017),
and the type material is deposited at the Musée
Géologique Cantonal, Lausanne, Switzerland (holotype
specimen MGL #68936).

OCCURRENCE
Ansermetite occurs sparingly at the Fianel Fe–Mn
mine near Ausserferrera, Ferrera Valley, Graubünden,
Switzerland (Brugger & Gieré 1999, 2000). Fianel is asmall Fe–Mn deposit of synsedimentary to diagenetic

origin, embedded in the Triassic carbonates of the
Suretta Nappe. It underwent a polyphase Tertiary metamorphism, climaxing at conditions of the blueschist to
greenschist facies. The following three stages of vanadate crystallization have been recognized at Fianel: (1)medaite (Mn,Ca)6(V,As)Si5O18(OH) crystallizes along
the main greenschist-facies Alpine schistosity (Brugger& Gieré 2000), (2) palenzonaite NaCa2Mn2(VO4)3,
saneroite Na2Mn10Vsi11O34(OH)4 and minor quantities
of pyrobelonite PbMnVO4(OH) occur in veinlets filledwith massive quartz, aegirine and rhodonite that crosscut the main schistosity, and (3) fianelite (Brugger &Berlepsch 1996), ansermetite and Fe oxyhydroxides
occur in thin fractures near or across the palenzonaitebearing veinlets. Fianelite and ansermetite represent thelatest stage in the remobilization of V that took place
during a late phase of the Tertiary Alpine metamorphism
or during recent supergene alteration.

APPEARANCE, PHYSICAL AND OPTICAL PROPERTIES
Ansermetite fills thin open fractures. The ansermetite
crusts reach a thickness of up to ~500 m and can cover
several square centimeters. The excellent cleavage ofansermetite can be observed on the rim of the polycrystalline crusts. Rare individual crystals up to 100 m
across display a typical monoclinic habit. An attempt toobtain SEM images of ansermetite crystals was unsuccessful, as the crystals “exploded” under the electron
beam and the vacuum. Even in the environmental scanning electron microscope (ESEM), we obtained only
poor photographs of single crystals of ansermetite(Fig. 1b). The Electroscan E3 ESEM was operated at
28 kV with a water vapor pressure of 5.7 Torr. Polishedsections reveal that the rim of many grains of ansermetite includes tiny (<10 m) crystals of As-poor
fianelite (Fig. 1a, Table 1).

ANSERMETITE, A NEW MINERAL SPECIES, EASTERN SWISS ALPSThe ansermetite crusts are bordeaux-colored,
whereas single crystals are carmine red. Ansermetite istransparent, with an orange streak and an adamantine
luster, and displays no fluorescence under ultraviolet
light. Optically, ansermetite is biaxial, with nmin = 1.797
and nmax = 1.856 (NaD, 22.5°C), and displays a strong
pleochroism between yellow orange (X) and ruby red(Z). The Mohs hardness is about 3. The good cleavageof ansermetite occurs along the monoclinic prism {110};the mineral is brittle with an uneven fracture. An average density of 2.57(2) g/cm3 has been measured on threegrains by immersion in a mixture of diiodomethane and1-chloronaphtalene. This value is slightly higher thanthe density of 2.49 g/cm3 derived from the crystal-structure refinement. The discrepancy may reflect the presence of fianelite inclusions, but may also be due to ion
exchange with the free H2O molecules located withintunnels of the structure (see below).

1425

counting times of 10 s on the peaks and 5 s on each sideof the peak for background. A tightly focused beam wasscanned over a ~25 m2 surface in order to minimize
sample damage. This surface had to be reduced to about3  3 m2 to analyze the small inclusions of fianelite.
The quality of the analytical procedure was verified byanalyzing simultaneously large (up to 5 mm) crystals ofreppiaite from Val Graveglia, Italy. The resulting empirical formula of reppiaite (average of four analyticalresults, normalized to a total of seven cations) is(Mn4.980Sr0.004)(OH)4(V1.843As0.161Si0.003)O8, sum =99.65%, in excellent agreement with the simplified formula Mn5(OH)4(VO4)2 (Basso et al. 1992). The empirical chemical formula obtained for ansermetite is(Mn0.99Sr0.004)(V1.99As0.013)O6•2H2O (Table 1).

CHEMICAL COMPOSITION
Chemical analyses were carried out with a Cameca
SX51 electron microprobe (Table 1), using the following probe standards: V: pure metal, As: synthetic GaAs,
Mn: rhodonite, and Sr: strontianite. No additional element with atomic number ≥ 9 was detected (<0.1 wt%).
The electron microprobe was operated at 15 kV, 20 nA,

F

a

A

b

FIG. 1. Paragenesis and morphology of ansermetite. (a) Reflected light microphotograph of a large crystal ofansermetite (A) with small crystals of fianelite (F; higher
reflectivity). The crystal is embedded in epoxy resin; a large
air bubble can be seen on the lower right. (b) Environmental scanning electron microscope image of the ansermetite.

1426

THE CANADIAN MINERALOGISTThe H2O content, equivalent to two H2O groups per
formula unit, was determined from the difference from
100% of the electron-microprobe-derived analytical totals. The value obtained is in conflict with that determined from the crystal-structure refinement, whichshows unambiguously that ansermetite contains 4 H2Ogroups per formula unit. This discrepancy is due to thepartial dehydration of ansermetite in the vacuum of theelectron microprobe (see below).

SINGLE-CRYSTAL X-RAY-DIFFRACTION STUDY
A platy reddish brown crystal fragment of ansermetite, about 0.01  0.05  0.20 mm3 in size and withperfect cleavage, was measured on a Bruker AXS threecircle diffractometer (equipped with a CCD 1000K area
detector and a flat graphite monochromator) using
MoK radiation from a fine-focus sealed tube (Table 2).
The SMART system of programs (Bruker AXS 1998)
was used for crystal-structure determination; the program SAINT+ (Bruker AXS 1999) was used for the data
reduction, including intensity integration, backgroundand Lorentz-polarization corrections. The program
XPREP (Bruker AXS 1997) was used for an empiricalabsorption-correction based on pseudo -scans. Fromthe space groups Cc and C2/c, raised as possibilities by
the program XPREP, the centrosymmetric C2/c waschosen in accordance with the results published by Liaoet al. (1996), but our choice is not fully in agreementwith the intensity statistics (| E2 – 1 | = 0.822). The unitcell content and dimensions for ansermetite and syn-thetic MnV2O6•4H2O are given in Table 3, and calculated and measured X-ray powder-diffraction patterns
are compared in Table 4.
The structure was solved by direct methods (program
SHELXS, Sheldrick 1997a), which revealed all cation
and O positions. In subsequent cycles of the refinement(program SHELXL, Sheldrick 1997b), four H positions
were deduced from the difference-Fourier syntheses byselecting from among the strongest maxima at appropriate distances. H–O distances were constrained to be
0.90(5) Å. The final refinement was performed withanisotropic displacement parameters for all but the H
positions (Tables 5, 6) and an empirical extinction-coefficient. The occupancy of the V site was refined andgave about 97% (full occupancy within six estimatedstandard deviations, Table 5). The refinement was
stopped when the mean shift/esd for varied parametersdropped below 1%. A table of structure factors is available from the Depository of Unpublished Data, CISTI,
National Research Council, Ottawa, Ontario K1A 0S2,
Canada.
The crystal structure of ansermetite is shown in
Figure 2. It is isotypic with the structures of synthetic
MnV2O6•4H2O (Liao et al. 1996) and CoV2O6•4H2O(Avtamonova et al. 1990). The structure contains V5+
in distorted square pyramidal coordination with fiveoxygen atoms, and Mn2+ in octahedral coordination withfour oxygen atoms and two H2O groups (Fig. 2a). The[VO5] polyhedra form infinite zigzag single chains
along [001] by sharing two of the four edges of the nearplanar square basis with two neighboring [VO5] poly-

FIG. 2. Crystal structure of ansermetite. (a) Projection of the structure on (001). Gray pyramids are [VO5] groups, and hatchedoctahedra are [MnO4(OH2)2]. The O5-centered H2O groups are shown; the O3-centered H2O groups belong to the[MnO4(OH2)2] octahedron and project on the O5 position on this projection. (b) View of the vanadate chains in ansermetite.
The spheres represent V5+ ions, and the “rods” represent bonds to O2– ions.

ANSERMETITE, A NEW MINERAL SPECIES, EASTERN SWISS ALPS

hedra (Figs. 2a, b). The two remaining oxygen atoms of
the [VO5] polyhedra are shared with two different[MnO4(OH2)2] octahedra. As a result, the metavanadate
single chains are connected by [MnO4(OH2)2] octahedra, which share four equatorial vertices with four [VO5]polyhedra belonging to two different chains (Fig. 2a).
The remaining opposite vertices of the [MnO4(OH2)2]octahedra are occupied by H2O molecules (O3). This
framework defines tunnels extending along [001], inwhich an additional H2O group is located (O5; Figs. 2a,3). A number of oxygen–oxygen distances lie in therange of strong to medium-strength hydrogen bonds(Table 7). Interestingly, the arrangement of the protons

1427

in the synthetic analogue is disordered (Liao et al. 1996).
Atom O3 linked to Mn is associated with four partly
occupied proton positions, whereas three proton sites
were resolved for O5. Although the structure refinementof natural ansermetite is of considerably lower quality(owing to crystal size and crystal quality) than the oneof the synthetic analogue (Liao et al. 1996), we wereable to extract an ordered arrangement of protons. The
protons labeled H3A and H5A form strong hydrogenbonds (Fig. 3) parallel to (001), enhancing the structuralchannels. Atom H3A forms a hydrogen bond (2.13 Å)
to O5, and H5A forms a hydrogen bond (2.17 Å) to O5
located across the cavity. H3B enhances the framework

FIG. 3. System of hydrogen bonds viewed approximately parallel to c. O3 is part of the
red Mn octahedron. O–H bonds are plain, and O…H hydrogen bonds are hatched. Onlyhydrogen bonds <2.2 Å are shown.

1428

THE CANADIAN MINERALOGISTof hydrogen bonds by connecting to the opposite O3(2.41 Å). H5B connects to O2 (2.12 Å). The low bondvalence at O2 (Table 8) is in line with acceptance of astrong hydrogen bond from H5B.

RELATION TO OTHER SPECIES
Ansermetite is the third known vanadate of manganese, after fianelite, Mn2V(V,As)O7•2H2O (Brugger &Berlepsch 1996) and reppiaite, Mn5(VO4)2(OH)4 (Basso
et al. 1992). Fianelite and ansermetite occur in close
association at the Fianel mine, whereas reppiaite is arare mineral occurring in the metamorphosed exhalative
deposits of manganese at Gambatesa, Val Graveglia,
Italy. Reppiaite forms under retrograde greenschist- tozeolite-facies conditions.
Ansermetite is the first natural vanadate of manganese in which V5+ occurs in five-fold square pyramidal
coordination. Evans & Hughes (1990) pointed out that
vanadium bronzes can be considered as various laterallinkages of only two types of polyvanadate chains: a
divanadate chain (V 2 O 6 ) n , of the type found inansermetite, and a tetravanadate chain (V4O12)n consisting of four chains of octahedra. Minerals containing

ANSERMETITE, A NEW MINERAL SPECIES, EASTERN SWISS ALPS

isolated divanadate chains similar to those found inansermetite include munirite, NaVO3•1.9H2O (Björnberg& Hedman 1977), metamunirite, NaVO3 (Kato &Takayama 1984), rossite, Ca(VO3)2•4H2O (Ahmed &Barnes 1963) and metarossite, Ca(VO3)2(H2O)2 (Kelsey& Barnes 1960).
Schindler et al. (2000a) used a bond-valence approach to rationalize the structural properties of vanadium minerals and the conditions of their formationfrom aqueous solution (i.e., pH of the mother solution).
They predicted that in a mineral formed in aqueous solution, a divalent cation in [6]-coordination occurring
together with the [V2O6] structural unit should bond toat least three transformer H2O groups. This prediction
was based on a comparison with rossite, metarossite,murinite and metamurinite. In ansermetite, [VI]Mn2+
bonds to two transformer H2O groups only, showing thatthe predictions for vanadate minerals do not exactly
match but are still in a reasonable range.

DEHYDRATION OF ANSERMETITE
Owing to recent interest in transition-metal oxide
electrodes for lithium batteries, studies of the system V–
Mn–O–H are available in the solid-state physics literature (e.g., Kim et al. 2001, Le Gal La Salle et al. 2000).
Ansermetite is easily synthesized at room temperatureby precipitation from a stoichiometric MnSO4•H2O andNaVO3 solution at pH in the range 4.5–6.5 (Liao et al.
1996). The precipitation of ansermetite reflects the presence of metavanadate complexes such as V 3O 93–,
V4O124– or HV10O285– in neutral to mildly acidic aqueous solutions at room temperature (e.g., Greenwood &Earnshaw 1984, p. 1148). Evans & Garrels (1958) firstpointed out the importance of pH in determining thespeciation and polymerization of V5+ in solution; this inturn determines the nature of precipitating minerals.
MnV2O6•4H2O appears to be stable only at low temperature at atmospheric pressure. Liao et al. (1996) observed a relatively complex mechanism of dehydration
as a function of H2O activity and chemistry of the medium (Fig. 4). In contact with the solution from which it
precipitated, MnV2O6•4H2O (ansermetite) transforms
rapidly at about ~100°C to a mixture of MnV2O6•2H2O

MnV2O6•H2O

Aqueous solution
pH 4.5~6.5
Pure water
Air

T
=

T = ~240˚CC
0˚

MnV2O6•2H2O+ MnV2O6•H2O

0~3

T = 105˚C~125˚C
160 hours

1429

α-MnV2O6

T = ~320˚C

β-MnV2O6

cooling
T = 105˚C~125˚C
6 hours
T = 85˚CT = 25˚C(γ)-MnV2O6
MnV2O6•2-4H2O
MnV2O6•4H2O
T = 110˚C~160˚C
T = 25˚C~95˚C T = 50˚C~90˚C
T = 85˚C, 48 hours

FIG. 4. Thermal stability of MnV2O6•4H2O at atmospheric pressure, in aqueous solution
and in air. Data from Liao et al. (1996).

1430

THE CANADIAN MINERALOGISTand MnV2O6•H2O. In the latter two compounds, vanadium has tetrahedral coordination (Liao et al. 1996). On
the other hand, MnV2O6•4H2O transforms to the anhydrous –MnV2O6, with a brannerite-type crystal structure within 2–3 days at 85°C in water. This reaction
appears to be irreversible. When heated in air,
MnV2O6•4H2O transforms at ~50°C into MnV2O6•2–
4H2O.
We also observed that the two weakly bound H2Ogroups per formula unit (O5) are easily released in
vacuum. This was first observed on polished sections:ansermetite showed a good initial polish, but came outof the EMP with a poor polish and prominently visible
cleavage. Similarly, an attempt to obtain SEM pictures
was unsuccessful, as the crystals exploded under theelectron beam in the vacuum. Even under wet ESEM
(5.7 Torr H2O pressure), ansermetite is unstable andhard to photograph. A Guinier powder X-ray photograph obtained under vacuum (~10–5 bar) confirmed thatwithin 40 minutes, a significant proportion of ansermetite is transformed into MnV2O6•2–4H2O. It therefore appears that ansermetite is highly reactive, owing
to the collapse of the structure as the weakly bound H2Ogroups escape.
The available information about the stability of
MnV2O6•4H2O suggests that ansermetite formed undernear-surface conditions (T < 50°C) from a neutral tomildly acidic groundwater. Ansermetite would probably
not survive under a hot dry climate, where surface temperatures in excess of 40°C can be attained. The occurrence of ansermetite can be compared to that of rossite,
Ca(VO3)2•4H2O, which also precipitates from neutral
aqueous solutions at room temperature (Ahmed &Barnes 1963). However, whereas ansermetite is stable
under room-temperature conditions, rossite slowly dehydrates to metarossite (Ahmed & Barnes 1963), andmurinite, to metamurinite (Kato & Takayama 1984).
Using the coordination-number descriptors [1 + 4] and[2 + 3] introduced by Schindler et al. (2000b), Schindler
et al. (2000a) showed that at the transition rossite–metarossite, the type of coordination of V5+ changes
from [1 + 4] to [2 + 3], whereas in munirite andansermetite, V5+ is already in [2 + 3] coordination.

ACKNOWLEDGEMENTS
We are grateful to John Terlet, Peter Self, Lyn
Waterhouse and Linda Matto from Adelaide Microscopy for help with the EMP and ESEM. We thankPhilippe Thélin (Université de Lausanne) for powder
XRD facilities. We also thank Stefan Ansermet andRoberto Bracco for providing the specimen ofansermetite, and for their patience with the pace of thisstudy. We are grateful to Michael Schindler, J.A.
Mandarino, Riccardo Basso and Robert F. Martin for
useful and stimulating reviews and many editorial improvements.

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Received April 5, 2003, revised manuscript accepted
October 22, 2003.