American Mineralogist, Volume 91, pages 937–943, 2006

Scheuchzerite, Na(Mn,Mg)9[VSi9O28(OH)](OH)3, a new single-chain silicateJOËL BRUGGER,1,* SERGEY KRIVOVICHEV,2,3 NICOLAS MEISSER,4 STEFAN ANSERMET,4
AND THOMAS ARMBRUSTER3
1

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, 5000 Adelaide, South Australia
2
Department of Crystallography, Faculty of Geology, St. Petersburg State University, University Emb. 7/9, 199034 St. Petersburg, Russia
3
Laboratorium für chemische und mineralogische Kristallographie, Universität Bern, Freiestrasse 3, CH-3012 Bern, Switzerland
4
Musée Géologique Cantonal and Laboratoire des Rayons-X, Institut de Minéralogie et de Géochimie, UNIL-BFSH2, CH-1015
Lausanne-Dorigny, Switzerland

ABSTRACT
Scheuchzerite, Na(Mn,Mg)9[VSi9O28(OH)](OH)3, is a new mineral from the metamorphosed synsedimentary exhalative Mn deposit of Fianel, Val Ferrera, Central Alps, Switzerland. It is dedicated to
the Swiss naturalist Johann Jakob Scheuchzer (1672–1733). Scheuchzerite is associated with saneroite
and tiragalloite in veins resulting from the remobilization of ore components during retrograde Tertiary
Alpine metamorphism. Scheuchzerite forms yellow-orange, transparent acicular crystals up to 0.5 mm
in length with yellow-orange streak and vitreous luster, Mohs’ hardness ~2.5, dcalc 3.47 (electron microprobe) to 3.52 g/cm3 (structure reÞnement); dmeas 3.50(2) g/cm3, good cleavage parallel to Þber elongation. Scheuchzerite is biaxial positive, nmin = 1.74 and nmax = 1.75; nmean (Gladstone-Dale) 1.74; weakly
pleochroic, X = brown yellow, Y = pale yellow. The empirical chemical formula is Na0.97(Mn7.79Mg0.95Z–
n0.16Ni0.04Ca0.03Al0.01)Σ=8.98 (V0.95As0.02Si9.08)Σ=10.05O32.05H4. Scheuchzerite is triclinic, P1, a = 9.831(5) Å, b
= 10.107(5) Å, c = 13.855(7) Å, α = 86.222(10)°, β = 73.383(9)°, γ = 71.987(9)°; V = 1254.2(10) Å3; Z= 2. The crystal structure was solved with direct methods on the basis of 1616 unique reßections with I> 4σF and reÞned to R1 = 9.4%. The crystal structure consists of tetrahedral layers separated by layers
containing chains of edge-sharing [Mn(O,OH)6] octahedra as well as [NaO8] polydedra. The tetrahedral
layers consist of [Si9O25(OH)] loop-branched chains of corner-sharing silicate tetrahedra extending along[011]. The loops contain 6 tetrahedra and are separated by 3 tetrahedra in a broken 4-loop arrangement. A
hydrogen atom is probably shared by two O atoms (symmetrical hydrogen bond), replacing the missing
silicon atom. A vanadate (VO4)3– tetrahedron branches off the 6-tetrahedra loop, and hence the overall
formula of the tetrahedral chains is [VSi9O28(OH)]. In the notation of Liebau (1985), scheuchzerite isa single chain silicate (monopolysilicate) {olB,11∞}[VSi9O28(OH)]. The topology of the scheuchzerite
structure is reminiscent of that of the double-chain silicates of the amphibole group, but scheuchzerite
contains a new type of silica chain.
Keywords: Scheuchzerite, new mineral, Fianel mine, Val Ferrera, Central Alps, Switzerland,
crystal structure, single chain silicate

INTRODUCTION
Metamorphosed Mn-rich deposits, such as those at Långban
in Sweden; the Kombat mine in Namibia; and at Franklin, New
Jersey, U.S.A., are among the richest mineralogical “rainforests”
on Earth (Pring 1995), and are still contributing a steady streamof new minerals. Many of these minerals contain arsenic or
vanadium as a major component. In this paper, we describe theoccurrence and mineralogy of a new sodium-manganese silicatevanadate, occurring in the small metamorphosed Mn-Fe depositof Fianel, canton Graubünden, Switzerland.
The new mineral is dedicated to the Swiss naturalist Johann
Jakob Scheuchzer (1672–1733). Scheuchzer was junior physicianof the city of Zürich, curator of the Kunstkammer—a cabinet of
natural history and curiosities—and he held the chair of physics
and mathematics at the University of Zürich. Scheuchzer’s work
* E-mail: joel.brugger@adelaide.edu.au
0003-004X/06/0506–937$05.00/DOI: 10.2138/am.2006.1965937

on Swiss geology and mineralogy was essential for his time; forexample, he studied Alpine quartz, measuring the angles of many
crystals (Scheuchzer 1708) and describing ßuid inclusions and gas
bubbles in the crystals (Scheuchzer 1718). The latter observation
was fundamental in invalidating Plinius’ popular theory that quartz
crystals consist of water irreversibly frozen by the great cold in
the mountains (Plinius the Old, 23–79 BC).
The new mineral and its name have been approved by theInternational Mineralogical Association (proposal number 2004044), and the type material is deposited at the Musée Géologique
Cantonal, Lausanne, Switzerland (Holotype specimen, MGL
79355).

OCCURRENCE
Scheuchzerite occurs sparingly at the Fianel Fe-Mn minenear Ausserferrera, Ferrera valley, Graubünden, Switzerland(Brugger and Gieré 1999, 2000). Fianel is a small Fe-Mn depositof syn-sedimentary to diagenetic origin, embedded in the Trias-

938

BRUGGER ET AL.: SCHEUCHZERITE, A NEW SINGLE-CHAIN SILICATEsic carbonates of the Suretta nappe. It underwent a polyphase
Tertiary metamorphism, climaxing under blueschist- to greenschist-facies conditions (Nussbaum et al. 1998). The following
three stages of vanadate crystallization have been recognized at
Fianel (Brugger and Gieré 2000): (1) crystallization of medaite(Mn,Ca)6(V,As)Si5O18(OH) along the main greenschist-facies Alpine schistosity; (2) formation of palenzonaite NaCa2Mn2(VO4)3,
saneroite Na2Mn10VSi11O34(OH)4, minor quantities of pyrobelonite
PbMnVO4(OH), tiragalloite Mn4AsSi3O12(OH), and scheuchzerite
in veinlets Þlled with massive quartz, aegirine, and rhodonite thatcross-cut the main schistosity; and (3) crystallization of Þanelite
Mn2V(V,As)O7·2H2O (type locality; Brugger and Berlepsch
1996), ansermetite MnV2O6·4H2O (type locality; Brugger et al.
2003), and Fe oxyhydroxides in thin fractures near or across thepalenzonaite-bearing veinlets.
Appearance, physical, and optical properties
Scheuchzerite occurs as acicular crystals up to 0.5 mm inlength and as smaller prismatic crystals Þlling veinlets up to 1
mm in width (Fig. 1). Scheuchzerite is yellow-orange in color
with a streak of similar color. The new species is intimately
associated with orange–red massive to prismatic saneroite,
and intergrowths of both minerals are common (e.g., Fig. 1).
Scheuchzerite is transparent with a vitreous luster. It does notßuoresce under the UV lamp. Optically, scheuchzerite is biaxial
positive, with nmin = 1.74 and nmax = 1.75. The refractive indiceswere measured at 24 °C by the immersion method (NaD light). The
refractive index of the liquid (Cargille Labs) was checked usinga Leitz-Jelley micro-refractometer. The average refractive index
is 1.74, calculated using the Gladstone-Dale relationship with theconstants of Mandarino (1976), the average chemical analysis of
Table 1 normalized to a sum of 100%, and a density of 2.50 g/cm3.
Scheuchzerite is weakly pleochroic, with X = brown yellow andY = pale yellow. The Mohs’ hardness was estimated by depositing
scheuchzerite fragments on fresh cleavages of gypsum, calcite,and ßuorite and rubbing them with a Teßon needle. Scheuchzerite
scratches only gypsum and therefore has a Mohs’s hardness be-

Snr

Qtz

Sz

200 µm
FIGURE 1. Scanning electron microscope image (Back Scattered
Electron mode) of acicular scheuchzerite crystals (Sz) partiallyintergrown with platy saneroite (Snr) in a vug lined with minute quartz(Qtz) crystals. Part of holotype specimen MGL 79355.

tween 2 and 3. Scheuchzerite is brittle and has a good cleavage–
parallel to [111], i.e., parallel to Þber elongation. The measured
density of 3.50(2) g/cm3 represents the average on three different
grains and was obtained by immersion in a thallium malonate/
formate (Clerici liquor)—water gradient tube. The solution at thelevel of the crystals was sampled using a chromatography syringe,
and its density was deduced from its refractive index. The density
calculated from the electron microprobe analyses (Table 1) andthe cell volume from the single crystal reÞnement (see below) is
3.47(1) g/cm3; calculated density based on the crystal structurereÞnement is 3.52 g/cm3.
Chemical composition
Chemical analyses were carried out with a Cameca SX51
electron microprobe (Table 1), using the following standards:
V, pure metal; As, synthetic GaAs; Si and Al, almandine; Mg,
forsterite; Mn, rhodonite; Ca, wollastonite; Na, albite; Ni,cobaltite; Zn, sphalerite. The microprobe was operated at 15
kV, 20 nA, peak counting times of 10 and 5 s on each side of
the peak for background. The beam was tightly focused. The
empirical chemical formula obtained for scheuchzerite, based
upon normalization on 20 cations per formula unit (pfu) and aÞxed content of 4 H atoms pfu is: Na0.97(Mn7.79Mg0.95Zn0.16Ni0.04
Ca0.03Al0.01)Σ=8.98(V0.95As0.02 Si9.08)Σ=10.05O32.05H4 (Table 1), in good
agreement with the chemical formula from the crystal structurereÞnement Na0.80(Mg,Na)0.20 (Mn8.57Mg0.43)[VSi9O28(OH)](OH)3(see below), and with the simpliÞed chemical formula Na(Mn,Mg)9[VSi9O28(OH)](OH)3.
The presence of water in the form of hydroxyl group was
TABLE 1. Electron microprobe analysis of scheuchzerite
V2O5
As2O5
SiO2
Al2O3
MgO
MnO
CaO
Na2O
NiO
ZnO
H2O
Sum

Average
6.46
0.14
41.02
0.04
2.86
41.54
0.13
2.25
0.22
0.96
2.71
98.33

Min
5.91
0.00
39.20
0.02
2.56
39.58
0.07
1.93
0.11
0.60
2.65
96.69

Max
6.84
0.31
44.10
0.07
3.15
42.35
0.17
2.38
0.37
1.27
2.71
98.55

Si
V
As
Sum

9.08
0.95
0.02
10.05

8.85
0.87
0.00
9.86

9.87
1.00
0.04
10.76

Mn2+
Mg
Zn
Ni
Ca
Al
Sum

7.79
0.95
0.16
0.04
0.03
0.01
8.98

7.50
0.85
0.00
0.00
0.02
0.00
8.41

8.03
1.05
0.21
0.07
0.04
0.02
9.16

Na

0.97

0.84

1.03

H
4.00
O
32.05
31.87
32.78
Notes: Average of 20 analyses. PbO ≤ 0.13 wt%; CuO ≤ 0.06; Cr2O3 < 0.05; FeO <0.05. No additional element with atomic number ≥9 was detected (<0.1 wt%).
Water content calculated on the basis of 4 H atoms pfu.
Empirical chemical formula: Na0.97(Mn7.79Mg0.95Zn0.16Ni0.04Ca0.03Al0.01) (V0.95As0.02Si9.08)
O32.05H4.

BRUGGER ET AL.: SCHEUCHZERITE, A NEW SINGLE-CHAIN SILICATEconÞrmed using an FT-IR spectrum (650 to 4000 cm–1) collected
on ground material with a Perkin Elmer Paragon 1000 FT-IR
equipped with a Graseby Specac ATR accessory (diamond topplate). A strong band at 1466 cm–1 is attributed to the stretchingmode of a H atom involved in a strong hydrogen bond, whereasa small band at around 3496 cm–1 is attributed to a H atom
involved in a weak hydrogen bond (Libowitzky 1999). No
absorption band was observed around 1600–1650 cm–1 (bending mode of H2O) indicating the absence of molecular water inscheuchzerite (Fig. 2).

939

all atoms, with an allowance for anisotropic displacement of Mn sites only, anda weighting scheme for the structure factors. The occupancies of the cation sites
were Þrst reÞned and then Þxed at the reÞned values with slight corrections tosatisfy the electroneutrality condition. The reÞnement of the structure converged
to an agreement index (R1) of 9.4%, which was calculated for the 1616 uniqueobserved reßections (Fo ≥ 4σFo). The relatively high R1 value is the consequenceof the relatively large mosaic spread, which suggests that the crystal under study isan aggregate of semi-paralell crystals, or consists of domains with slightly different
orientations. Final positional and displacement parameters of atoms, bond-valencesums, and selected interatomic distances are listed in Tables 4, 5, and 6.

Powder X-ray diffraction study
The X-ray powder diffraction pattern of scheuchzerite wascollected using a 114.6 mm diameter GandolÞ camera andCuKα/Ni-Þltered X-ray radiation. The powder pattern is in good
agreement with the results of the crystal-structure analysis in termsof the comparison between calculated and observed d-spacings andintensities (Table 2). The unit-cell parameters calculated using theleast-squares method on the basis of 18 unambiguously indexed
reßections (program UnitCell, Holland and Redfern 1997) are: a= 9.83(1) Å, b = 10.12(2) Å, c = 13.89(2) Å, α = 86.4(1)°, β =73.25(10)°, γ = 71.9(1)°, V = 1258(2) Å3, in good agreement withthose obtained by single crystal diffraction (Table 3).

SINGLE-CRYSTAL X-RAY DIFFRACTION STUDY
Experimental methods
A prismatic crystal fragment of scheuchzerite, about 80 × 30 × 6 μm3 in size,
was mounted on a Bruker AXS three-circle diffractometer equipped with a CCD 1
K area detector and a ßat graphite monochromator. More than a hemisphere of data
was collected with an exposure time of 300 s and frame widths of 0.3° in ω using
MoKα-radiation from a Þne focus sealed tube. The unit-cell dimensions (Table 3)
were determined from least-squares reÞnement of 1014 reßections. The data werereduced and Þltered for statistical outliers using the Bruker program SAINT, and werecorrected for Lorentz, polarization, and background effects. An empirical absorption
correction based on 195 reßections was applied assuming an ellipsoidal crystal shape.
This correction lowered Rint from 9.4 to 7.7%. Additional information pertinent to thedata collection is given in Table 3.
The Bruker SHELXTL Version 5 package was used for the determination andreÞnement of the structure. The structure was solved initially in the non-centrosym–
metric triclinic group P1 and later transformed into the centrosymmetric group P1
using the PLATON program (Spek 2005). The structure was reÞned on the basisof F2 for all unique data. The Þnal reÞnement included positional parameters of

FIGURE 2. Infrared spectra of scheuchzerite and saneroite from
Fianel, Val Ferrera, Switzerland.

TABLE 2.

Measured and calculated powder diffraction data forscheuchzerite

h
k
l
dcalc
Icalc
dmeas
Imeas
1
0
1
8.64
53
8.68
50
1
1
0
7.86
70
7.91
70
2
1
1
4.82
21
4.83
30
0
2
0
4.80
9
2
0
2
4.32
12
4.32
20
–
0
1
3
4.06
5
4.08
10
–
0
2
2
3.94
4
–
2
0
1
3.93
6
3.94
30
2
2
0
3.93
10
–
1
2
1
3.78
7
3.79
30
2
2
2
3.77
5
–
2
1
1
3.77
8
–
1
2
2
3.72
8
3.74
10
1
3
0
3.36
5
2
2
3
3.33
10
3.35
10
3
1
1
3.27
9
3.26
10
3
1
2
3.22
27
3.22
40
2
3
1
3.13
14
3.13
20
2
0
4
3.12
4
–
1
2
3
3.09
6
–
2
2
2
3.09
20
3.09
80
2
3
0
3.09
7
3
2
1
3.08
51
3
0
2
3.07
10
3.02
10
–
1
3
2
2.905
35
2.92
40
1
1
5
2.706
100
2.71
100
–
2
2
1
2.702
85
–
3
1
2
2.698
9
0
0
5
2.654
14
2.66
30
–
1
3
1
2.649
17
–
0
3
3
2.625
35
2.63
30
–
3
1
4
2.380
16
2.38
10
–
3
1
3
2.273
19
2.27
10
2
4
3
2.270
16
2
1
6
2.255
17
2.26
30
–
3
2
0
2.251
21
–
2
4
2
2.209
37
2.22
30
–
1
4
3
2.141
6
2.15
10
–
3
4
1
2.138
7
3
2
6
2.053
21
2.06
30
–
4
1
0
2.052
18
4
2
7
1.721
7
–
5
1
1
1.720
10
1.72
10
–
4
5
1
1.688
18
1.69
20
–
5
2
2
1.687
8
4
5
4
1.686
6
–
1
3
6
1.643
30
1.64
30
6
3
3
1.606
8
–
1
2
8
1.603
16
1.61
40
–
2
5
0
1.600
15
–
1
3
7
1.598
8
–
0
6
1
1.595
8
1.58
10
5
3
7
1.536
8
1.53
10
6
3
5
1.535
6
–
0
3
8
1.488
9
1.49
20
–
1
6
2
1.485
10
Notes: Gandolfi camera, 114.6 mm, CuKα/Ni-filtered, 40 kV, 30 mA, 99 h exposure
time. Intensities were visually estimated. The calculated intensities are from thecrystal structure analysis.

940

BRUGGER ET AL.: SCHEUCHZERITE, A NEW SINGLE-CHAIN SILICATETABLE 3. Crystallographic data and refinement parameters for
scheuchzeritea (Å)
9.831(5)b (Å)
10.107(5)c (Å)
13.855(7)α (°)
86.222(10)β (°)
73.383(9)γ (°)
71.987(9)31254.2(10)V (Å )–Space groupP1
5.20
μ (mm–1)
Z
2
Cell content
Na0.80(Mn8.57Mg0.63)[VSi9O28(OH)](OH)3
3
Dcalc (g/cm )3.52
30.08 × 0.03 × 0.006
Crystal size (mm )Diffractometer
Bruker SMART 1K
Radiation
MoKαTotal Ref.
7467
Unique Ref.
5441
1616
Unique |Fo| ≥ 4σF
0.077
Rint
0.094
R1
0.166
wR2
0.781
S
Notes: R1 = Σ(|Fo| – |Fc|)/Σ|Fo|; wR2 = {Σ[w(Fo2 – Fc2)2]/Σ[w(Fo2)2]}½; w = 1/[σ2(Fo2) + (aP)2+ bP], where P = (Fo2 + 2Fc2)/3; S = [Σw(|Fo| – |Fc|)2/(n – p)]½.

Crystal structure
The structure of scheuchzerite contains nine symmetricallyindependent Mn sites each octahedrally coordinated by six anions(O and OH). The average <Mn-O> bond lengths are in the rangeof 2.15–2.26 Å, whereas individual bond lengths vary from 2.067
to 2.530 Å (Table 6). During reÞnement, it was noticed that the
Mn4, Mn7, and Mn8 sites are under-occupied if reÞned using
the Mn scattering factor. Taking into account the considerable
amount of Mg in the structure, the occupancies of these sites werereÞned by means of mixed Mn-Mg scattering curves (Table 4).
There is one independent Na site in the structure that is surrounded by 8 O atoms with distances between 2.39 and 3.07
Å. This Na site has an occupancy of 80% calculated on thebasis of Na. This is seemingly in disagreement with the resultsof chemical analysis that gives 0.97 Na per formula unit. The
possible explanations for this disagreement are: (1) the crystal
studied had slightly different chemical composition; and (2) some
Na is incorporated into Mn sites or the disordered Mg site. The
disordered Mg site has a very low occupancy of 20% and may,in fact, represent a highly disordered site that accommodates
excessive amounts of both Na and Mg that do not Þt into theMn sites (Table 4).
The V site in the structure of scheuchzerite is split into two sites,
V1 and V1A, that have occupancies of 89% and 11%, respectively.
The overall coordination of these sites is tetrahedral; however, bondlengths are deÞnitely in error, especially for the V1A site, becauseof the disorder. This leads to a low bond valence sum for the V1Asite (Tables 4 and 6).
The bond-valence sums for the cation and anion sites are given in
Table 4. Bond-valence sums for all sites with occupancies exceeding
50% are in good agreement with their expected values. The bondvalence sums for O26 and O29 sites are 1.48 and 1.53 v.u., respectively. The O26...O29 distance is 2.35 Å. Note that these atoms are
not part of the same coordination polyhedron, which may indicate asymmetrical O...H...O hydrogen bond between the O26 and O29 sites.
Another possible conÞguration is a disordered hydrogen bond with
the O26 and O29 sites occupied by O and OH in equal proportion.

TABLE 4.

Atomic coordinates, displacement parameters (Å 2),
and bond-valence sums (BVS, v.u. = valence units) for
scheuchzerite

Atom Occupancy BVSxy
Mn1
Mn1.002.00
0.0757(3) 0.8310(3)2.05
0.5671(3) 0.6937(3)Mn2
Mn1.001.89
0.1538(3) 0.0823(3)Mn3
Mn1.000.7129(3) 0.3634(3)Mn4 Mn0.93Mg0.07 2.14
1.86
0.7499(3) 0.4835(3)Mn5
Mn1.002.21
0.3262(3) 0.7645(3)Mn6
Mn1.000.4794(3) 0.4353(3)Mn7 Mn0.84Mg0.16 2.29
0.6306(3) 0.1039(3)Mn8 Mn0.80Mg0.20 2.04
1.97
0.1425(3) 0.9711(3)Mn9
Mn1.000.93
0.131(1)0.4358(9)NaNa0.801.73
0.109(5)0.557(5)Mg
Mg0.204.77
0.8167(4) 0.2386(3)
V1
V0.89
2.85
0.951(3)0.297(3)
V1A
V0.11
Si1
Si
4.20
0.4550(5) 0.7412(5)
Si2
Si
4.05
0.2825(5) 0.0474(5)
Si3
Si
4.21
0.0371(5) 0.1425(5)Si4Si
4.11 –0.5200(5) 0.1836(5)
Si5
Si
4.28
0.6926(5) 0.6304(5)
Si6
Si
4.10
0.9340(6) 0.5555(5)
Si7
Si
4.30
0.0804(5) 0.2371(5)
Si8
Si
4.34
0.7539(6) 0.7385(5)
Si9
Si
4.06
0.8450(5) 0.3251(5)
O1
O
2.02
0.3109(12) 0.6926(11)
OH2
OH
1.15
0.4944(12) 0.4802(11)
O3
O
2.17
0.5457(12) 0.6038(11)O4O
2.03 –0.0682(12) 0.2056(11)O5O
2.03 –0.0988(12) 0.0925(11)
O6
O
1.95
0.1432(12) 0.0098(11)
O7
O
2.11
0.6968(12) 0.2872(11)OH8OH
1.17† 0.2692(12) 0.5927(11)O9O
1.91‡ 0.9164(13) 0.1186(12)O10O
2.06 –0.3615(13) 0.1939(12)
O11
O
2.02
0.7892(12) 0.5351(11)
OH12
OH
1.10
0.3811(12) 0.9364(11)
O13
O
1.94
0.1507(12) 0.0328(11)
O14
O
2.01
0.5975(12) 0.7299(11)
O15
O
1.96
0.6667(13) 0.1889(12)
O16
O
1.98
0.5537(12) 0.6440(11)O17O
2.17‡ 0.7899(12) 0.8761(11)O18O
2.05‡ 0.9266(12) 0.2407(11)O19O
1.82‡ 0.7603(13) 0.4006(12)O20O
1.97‡ 0.0202(12) 0.6468(11)O21O
2.34† 0.8117(12) 0.4896(11)O22O
2.21† 0.0649(12) 0.4020(11)O23O
2.06† 0.7716(13) 0.7015(12)O24O
2.26† 0.1109(12) 0.1989(11)
O25
O
2.09
0.3949(13) 0.9012(12)0.3661(12) 0.1245(11)O,OH26 O0.5(OH)0.5 1.48
O27
O
2.13
0.2245(12) 0.1509(11)O28O
1.98†,‡ 0.8894(13) 0.6113(12)O,OH29 O0.5(OH)0.5 1.53 –0.5246(13) 0.0258(12)O30O
1.93† –0.0300(12) 0.2863(11)
O31
O
2.16
0.6573(13) 0.7324(11)
O32
O
2.01
0.5579(12) 0.7320(11)* Fixed during refinement.
† Assuming neighboring Mg site is vacant.
‡ Assuming V1 is occupied (V1A vacant).

z0.0136(2)0.1599(2)0.5619(2)0.1903(2)0.9689(2)0.5880(2)0.6140(3)0.6374(2)0.7869(2)0.2935(7)0.649(4)0.7693(3)0.770(2)0.9501(4)0.9656(4)0.3656(4)0.2658(4)0.5435(4)0.1366(4)0.1490(4)0.3257(4)0.5500(4)0.9527(8)0.7588(8)0.5341(9)0.1429(8)0.3562(9)0.9403(9)0.5556(9)0.6638(9)0.8378(9)0.2723(9)0.1161(9)0.5120(9)0.4170(9)0.3174(9)0.7688(9)0.0175(9)0.3067(8)0.6354(9)0.8198(9)0.0628(9)0.5668(9)0.1387(9)0.4420(9)0.2573(9)0.9902(9)0.8720(9)0.0643(9)0.2559(9)0.2672(9)0.4368(9)0.6382(9)0.8333(8)Ueq0.0085(10)0.0114(7)0.0146(10)0.0096(10)0.0107(7)0.0085(10)0.0127(12)0.0111(7)0.0126(10)0.026(3)0.050(18)0.010*
0.010*
0.0058(11)0.0097(12)0.0058(11)0.0102(12)0.0080(11)0.0113(12)0.0092(12)0.0130(12)0.0097(12)0.007(3)0.010(3)0.010(3)0.007(3)0.011(3)0.011(3)0.012(3)0.010(3)0.016(3)0.015(3)0.010(3)0.010(3)0.010(3)0.011(3)0.016(3)0.013(3)0.009(3)0.013(3)0.019(3)0.013(3)0.013(3)0.012(3)0.018(3)0.016(3)0.019(3)0.011(3)0.016(3)0.019(3)0.020(3)0.017(3)0.017(3)0.009(3)The symmetrical hydrogen bond conÞguration is supported by bondvalence considerations and by the IR data. The bond-valence sumson the O atoms of symmetrically bonded (OH)– groups are typically~1.5 v.u., excluding the H-atom contribution (Burns and Hawthorne
1994a, 1994b; Cahill et al. 2001), in agreement with those observed
for the O26 and O29 sites in scheuchzerite. Furthermore, the IR bandat 1466 cm–1 (Fig. 2) indicates a hydrogen bond between O atoms
less than ~2.5 Å apart, in agreement with the O26-O29 distance of
2.35 Å (Libowitzky 1999). The IR band at 3496 cm–1 is related to ahydrogen bond between O atoms separated by 2.8 to 3.0 Å (Libowitzky 1999), suggesting weak hydrogen bonding between OH12 andOH12 (2.95 Å) or between OH2 and OH19 (2.87 Å).

BRUGGER ET AL.: SCHEUCHZERITE, A NEW SINGLE-CHAIN SILICATEThe crystal structure of scheuchzerite consists of tetrahedral layers
separated by layers containing chains of edge-sharing [Mn(O,OH)6]
octahedra as well as [NaO8] polyhedra (Fig. 3a). The layers areparallel to (211). The tetrahedral layers consist of [Si9O25(OH)] loopbranched chains of corner-sharing silicate tetrahedra extending along[011] (Fig. 4a). The loops contain 6 tetrahedra and are separated by 3
tetrahedra in a broken 4-loop arrangement. A hydrogen atom is probably shared by two O atoms, replacing the missing silicate tetrahedron(Fig. 4a). A vanadate (VO4)3– tetrahedron branches off the 6-tetrahedra loop, and hence the overall formula of the tetrahedral chains is[VSi9O28(OH)]. There is only one type of chain (multiplicity = 1) andthe periodicity is 7. In the notation of Liebau (1985), scheuchzerite isa single chain silicate (monopolysilicate) {olB,11∞}[VSi9O28(OH)].
TABLE 5.

Anisotropic-displacement parameters (Å2) for the Mn sites
in the structure of scheuchzerite

Atom
U11
Mn1 0.0069(16)Mn2 0.0094(15)Mn3 0.0151(18)Mn4 0.0104(18)Mn5 0.0104(15)Mn6 0.0084(18)Mn7 0.012(2)Mn8 0.0110(16)Mn9 0.0141(19)

U22
U33
U23
U13
U12
0.0062(16) 0.0068(17) –0.0010(12) 0.0003(12) 0.0041(12)0.0117(16) 0.0097(17) –0.0052(12) –0.0017(13) 0.0018(13)0.0133(17) 0.0107(18) –0.0037(13) –0.0021(13) 0.0019(13)0.0072(17) 0.0079(19) –0.0017(13) –0.0014(14) 0.0012(13)0.0099(15) 0.0060(16) 0.0005(12) –0.0007(12) 0.0037(12)0.0105(18) 0.0042(18) –0.0009(13) –0.0009(13) 0.0000(14)0.011(2)0.012(2) –0.0016(15) –0.0003(16)–0.0022(15)0.0117(15) 0.0061(16) –0.0017(12) –0.0010(13) 0.0021(13)0.0124(17) 0.0048(17) –0.0036(12) 0.0017(13) 0.0019(13)TABLE 6. Selected distances (Å) in the structure of scheuchzerite
Mn1-O20
Mn1-O9
Mn1-O6
Mn1-O6
Mn1-O1
Mn1-O4<Mn1-O>

2.116(11)2.182(12)2.199(12)2.202(11)2.248(11)2.250(11)2.20

Mn2-O,OH26
Mn2-O16
Mn2-OH2
Mn2-O15
Mn2-O11
Mn2-O14<Mn2-O>

2.116(11)2.118(12)2.174(11)2.199(12)2.217(11)2.352(12)2.20

Mn3-O13
Mn3-O17
Mn3-O5
Mn3-OH12
Mn3-O18
Mn3-O23<Mn3-O>

2.112(12)2.148(11)2.162(11)2.204(11)2.300(12)2.504(11)2.26

Mn4-OH2
Mn4-OH8
Mn4-O11
Mn4-O1
Mn4-O10
Mn4-O4<Mn4-O>

2.118(11)2.164(12)2.181(11)2.189(11)2.192(11)2.193(11)2.17

Mn5-O16
Mn5-O20
Mn5-O1
Mn5-O19
Mn5-O11
Mn5-O22<Mn5-O>

2.067(12)2.169(12)2.176(11)2.245(13)2.301(12)2.530(11)2.25

Mn6-OH12

2.106(11)Mg-OH8Mg-O30
Mg-O28Mg-O23
Mg-O24
Mg-O21
Mg-O22<Mg-O>

1.78(5)2.01(5)2.08(5)2.74(5)2.82(5)2.90(5)2.93(5)
2.47

V1-O19V1-O15
V1-O9
V1-O18<V1-O>

1.686(12)1.701(11)1.725(12)1.863(12)1.74

V1A-O19
V1A-O28
V1A-O9V1A-O18<V1-O>

1.80(3)2.00(3)2.05(3)2.07(3)
1.98

Si1-O16
Si1-O25
Si1-O1
Si1-O32<Si1-O>1.608(12)1.617(12)1.628(11)1.636(12)1.62

Si2-O,OH26
Si2-O25
Si2-O27
Si2-O6<Si2-O>1.619(12)1.630(12)1.632(13)1.661(11)1.64

Si3-O13
Si3-O5
Si3-O24
Si3-O30<Si3-O>

1.603(11)1.607(11)1.619(12)1.657(12)1.62

Si4-O,OH29
Si4-O101.608(12)1.622(12)941

According to the Chemical Structural Mineral ClassiÞcation System of Strunz and Nickel (2001), scheuchzerite can be classiÞed as
inosilicate with 7-periodic chain (9.DO.).

RELATION TO OTHER SPECIES
Scheuchzerite is related to saneroite Na2Mn10VSi11O34(OH)4(Lucchetti et al. 1981), a mineral with which it is intimately associated. Both minerals are chain silicates, but saneroite contains
simple chains (Basso and Della Giusta 1980) with periodicityof 5 (Fig. 4b). A tetrahedron labeled Si6 branches off the chain,and consists of 50% Si and 50% V (Fig. 4b). The saneroite chain
can be seen as a distorted fragment of the scheuchzerite chain(numbered tetrahedra in Figs. 4a and 4b). The scheuchzerite chain
is obtained by completing the saneroite chain with 3 additional
silicate tetrahedra, corresponding to 6a, 6b, and 7 in Figure 4a.
It is therefore possible that the intergrowth commonly observed
among scheuchzerite and saneroite represents epitaxial growthalong the extension of the silicate chains (Fig. 1).
Similarly to the structure of scheuchzerite, saneroite contains[Mn(O,OH)6] octahedra that form chains; however, the chains
have different topology (2-2-3-3 in saneroite; 3-3-4-4-4 inscheuchzerite; Figs. 5a and 5b). The disordered V1A site (11%occupancy) is located in the space left by the missing octahedron

TABLE 6.—Continued
Mn6-OH8
Mn6-O10
Mn6-O7
Mn6-O5
Mn6-O3<Mn6-O>

2.110(11)2.150(12)2.179(12)2.201(12)2.219(12)2.16

Mn7-O14
Mn7-O3
Mn7-OH8
Mn7-OH2
Mn7-O7
Mn7-O3<Mn7-O>

2.103(11)2.139(11)2.139(12)2.141(12)2.157(12)2.209(12)2.15

Mn8-O,OH29
Mn8-O13
Mn8-OH12
Mn8-O15
Mn8-O7
Mn8-O14<Mn8-O>

2.092(12)2.115(11)2.178(12)2.223(12)2.278(11)2.291(12)2.20

Mn9-O17
Mn9-O6
Mn9-O4
Mn9-O9Mn9-O10
Mn9-O5<Mn9-O>

2.095(11)2.190(12)2.200(11)2.203(12)2.245(12)2.314(12)2.21

Na-O21
Na-O19Na-O22
Na-O24
Na-O31
Na-O28
Na-O30Na-O32<Na-O>

2.390(15)2.476(14)2.484(15)2.556(15)2.616(14)2.653(15)2.831(14)3.071(14)2.63

Si4-O32
Si4-O31<Si4-O>

1.642(11)1.651(13)1.63

Si5-O3
Si5-O31
Si5-O21
Si5-O23<Si5-O>1.590(11)1.613(13)1.621(12)1.638(12)1.61

Si6-O20
Si6-O11
Si6-O28
Si6-O22<Si6-O>1.575(12)1.603(11)1.672(13)1.687(12)1.63

Si7-O27
Si7-O24
Si7-O4
Si7-O22<Si7-O>

1.601(13)1.611(12)1.614(11)1.626(11)1.61

Si8-O17
Si8-O14
Si8-O28
Si8-O23<Si8-O>1.527(11)1.603(11)1.652(13)1.676(13)1.61

Si9-O7
Si9-O21
Si9-O18
Si9-O30<Si9-O>1.598(11)1.611(12)1.661(12)1.675(12)
1.64

942

BRUGGER ET AL.: SCHEUCHZERITE, A NEW SINGLE-CHAIN SILICATEF IGURE 3. Stacking ofoctahedral and tetrahedral
layers in (a) scheuchzerite;(b) tremolite (Hawthorne andGrundy 1976), and (c) pectolite(Ohashi and Finger 1978).
Octahedral sites represented asgray octahedrons; tetrahedral
sites as striped tetrahedrons; andseven- and eight-coordinatedsites are drawn as atoms andbonds. The gray tetrahedronlocated in the octahedral layer
ofscheuchzerite corresponds ofthe highly disordered V1A site,
and the gray tetrahedron in thetetrahedral layer corresponds
to V1.

SI4

SI9
SI7

SI5
SI10

SI8

SI4
SI9

5a

3
4

6a
7

SI2
SI4
SI9

SI5

2

SI1

5b
6b

SI1

2

SI2

3
5a

4

SI4
5b

SI10

SI8

SI3

SI2

SI5

SI7

1

SI3

1

SI4

SI6

SI3

SI1

SI5
SI10
SI3

O-H-O group(a) Scheuchzerite
projection on (211)(c) Pyroxmangite projection on (301)(b) Saneroite
projection on (3-13)(d) Synth. Mn7[Si7O21]
projection on (551)

F I G U R E 4 . Te t r a h e d r a lchains in the structures of (a)scheuchzerite; (b) saneroite(Basso and Della Giusta 1980),(c) pyroxmangite (Ohashi and
Finger 1975) and (d) synthetic
Mn7[Si7O21] (Ohashi and Finger
1978). The silicon sites and chain
periodicities are labeled in the
structures of scheuchzerite andsaneroite. The grayed tetrahedra
contain vanadium in scheuchzeriteand 50% silicon and vanadium insaneroite.

BRUGGER ET AL.: SCHEUCHZERITE, A NEW SINGLE-CHAIN SILICATE

c

b
a

943

FIGURE 5. Topology of the octahedral layers inthe structures of (a) scheuchzerite and (b) saneroite.
The dark gray tetrahedral site corresponds to thehighly disordered V1A site (11% occupancy).

cb(a) Scheuchzerite, projection on (100)(b) Saneroite, projection on (101)in the 3-octahedral units of scheuchzerite (Fig. 5a). The [NaO8]
polyhedra link two octahedral chains in saneroite, but are connected to only one in scheuchzerite.
Generally, the topology of the scheuchzerite structure isreminiscent of that of the double-chain silicates of the amphibole group (Fig. 3b) or of pyroxenoids such as pectolite (Fig.
3c). The only known silicates with a periodicity of 7 are pyroxmangite (Fig. 4c), pyroxferroite (Burnham 1971) and synthetic
Mn7[Si7O21] described by Narita et al. (1977; Fig. 4d); none ofthese contain loops.

ACKNOWLEDGMENTS
We are grateful to John Terlet, Peter Self, and Linda Matto (Adelaide Microscopy) for help with the EMP, to Pascal Tschudin and Peter O. Baumgartner (SEM/EDXS laboratory, Institute of Geology and Paleontology, UNIL, Lausanne) for thehelp with the SEM, and to Kiyotaka Ishida, Simona Quartieri and an anonymous
reviewer for helpful comments. Special thanks to Philippe Thélin (XRD laboratory, Institute of Mineralogy and Geochemistry, UNIL, Lausanne) for providing
XRD-powder micro-analysis facilities.

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