1195
The Canadian Mineralogist
Vol. 46, pp. 1195-1205 (2008)
DOI : 10.3749/canmin.46.5.1195

PSEUDOSINHALITE, MAGNESIOTAAFFEITE-6N’3S
AND MAGNESIOTAAFFEITE-2N’2S AS REPLACEMENT PRODUCTS OF SPINELIN DOLOMITE MARBLE FROM STUBENBERG, STYRIA, AUSTRIA
Franz BERNHARD§, Christoph HAUZENBERGER and Franz WALTER
Institute of Earth Sciences, Department of Mineralogy and Petrology, Karl-Franzens-University Graz,
Universitätsplatz 2, A–8010 Graz, Austria

Roy KRISTIANSENPO Box 32, N-1650 Sellebakk, Norway

Abstract
Pseudosinhalite [ideally Mg2Al3O(BO4)2(OH)] and magnesiotaaffeite-6N’3S (ideally BeMg2Al6O12), with rare lamellae ofmagnesiotaaffeite-2N’2S (ideally BeMg3Al8O16) occur as replacement products of spinel in geikielite–ilmenite – baddeleyite– zirconolite veins within polymetamorphic dolomite marble at Stubenberg, Styria, Austria. The crystallization sequence of
Mg–Al phases is spinel ! pseudosinhalite ! magnesiotaaffeite minerals, and spinel formed after or during the replacement of
baddeleyite by zirconolite. Pseudosinhalite contains up to 2.2 wt.% TiO2, 1.4% Cr2O3, and 1.3% FeO, whereas magnesiotaaffeite minerals contain up to 6.6 wt.% ZnO, 2.4% FeO, and 1.8% Cr2O3. The replacement of spinel by a Mg–Al borate and by
Mg–Al–Be oxides requires an influx of B and Be, respectively, since no B- or Be-bearing minerals are present in the original
assemblage. These elements are likely derived from fluids released from a Permian granite and pegmatites, or from Eo-Alpine
metamorphic fluids that have interacted with B- and Be-bearing lithologies.
Keywords: pseudosinhalite, magnesiotaaffeite-6N’3S, magnesiotaaffeite-2N’2S, spinel, geikielite, ilmenite, marble, Eastern Alps,
Stubenberg, Austria.

Sommaire
Nous documentons la présence de pseudosinhalite [formule idéale: Mg2Al3O(BO4)2(OH)] et magnésiotaafféite-6N’3S(formule idéale: BeMg2Al6O12), avec de rares lamelles de magnésiotaafféite-2N’2S (formule idéale: BeMg3Al8O16) en remplacement du spinelle dans des veines à geikielite–ilménite – baddeleyite – zirconolite recoupant un marbre dolomitique polymétamorphisé à Stubenberg, Styrie, en Autriche. La séquence de cristallisation de ces phases magnésiennes et almineuses serait: spinelle! pseudosinhalite ! minéraux du groupe de la magnésiotaafféite; le spinelle se serait formé après ou pendant le remplacement
de la baddeleyite par la zirconolite. La pseudosinhalite contient jusqu’à 2.2% TiO2, 1.4% Cr2O3, et 1.3% FeO (poids), tandis
que les minéraux du groupe de la magnésiotaafféite contiennent jusqu’à 6.6% ZnO, 2.4% FeO, et 1.8% Cr2O3. Le remplacement
du spinelle par un borate de Mg–Al et par des oxydes de Mg–Al–Be nécessite un apport de B et de Be, respectivement, parcequ’aucun minéral porteur de ces éléments n’est présent dans l’assemblage originel. Ces éléments auraient été dérivés soit d’une
phase fluide issue d’un granite ou de pegmatites permiens, soit d’un fluide métamorphique éo-Alpin équilibré avec des roches
contenant le bore et le béryllium.
(Traduit par la Rédaction)
Mots-clés: pseudosinhalite, magnésiotaafféite-6N’3S, magnésiotaafféite-2N’2S, spinelle, geikielite, ilménite, marbre, Alpes
orientales, Stubenberg, Autriche.

§

E-mail adress: bernhard11at@yahoo.de

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Introduction
The compound Mg 2Al 3O(BO 4) 2(OH) was first
synthesized in the course of experimental work on
the phase relationships of borates and borosilicatesand was predicted to occur as a primary mineral in
Mg–Al–B-rich rocks subjected to amphibolite facies
to lower-grade conditions, or as a retrograde productof the anhydrous Mg–Al borate sinhalite (Daniels et al.
1997 and references therein). Just before the final proofsof galleys for Daniels et al. (1997) were produced, anatural occurrence of this compound, which was named
pseudosinhalite, was discovered in the Tayozhnoyeskarn deposit, Siberia, where it occurs as a replacement
product of sinhalite (Schreyer et al. 1998). However, themineral was found only in a single thin section. Since
then, no further occurrences of pseudosinhalite havebeen reported. In this work, we present petrographic,
chemical and X-ray data on a second occurrence ofpseudosinhalite. It is found together with magnesiotaaffeite-6N’3S and magnesiotaaffeite-2N’2S (formerly
known as “musgravite” and “taaffeite”, respectively:
Armbruster 2002) as a product of replacement ofspinel in geikielite–ilmenite – baddeleyite – zirconolite
veins within polymetamorphic dolomite marbles from
Stubenberg in Styria, Austria.

Methods
Minerals were analyzed on carbon-coated polishedthin sections with a SEM JEOL JSM 6310 equippedwith an Oxford Link ISIS EDX spectrometer and a
Microspec WDX spectrometer at the Institut für Erdwissenschaften, Karl-Franzens-Universität Graz. Analyticalconditions were: accelerating voltage 15 kV, and probe
current 12 nA. As standards, we used synthetic spinel(Mg, Al), garnet (Fe), titanite (Ti), chromite (Cr),vanadinite (V), and gahnite (Zn). Detection limits ofthe EDX spectrometer are in the range 0.1–0.2 wt.%.
The grains were analyzed for fluorine and sodium with
the WDX system, with a detection limit of about 0.03
wt.%. A chromite standard containing 1.10 wt.% V2O3
and 1.60% TiO2 was used to check the accuracy of
V and Ti results. Proper correction of TiKb overlap
with VKa was monitored with a vanadium-free rutile
standard, which gave negligible values for vanadium.
Spinel and sinhalite from Johnsburg, New York, USA,and magnesiotaaffeite-6N’3S from the type locality,
Musgrave Ranges, Australia, were analyzed forcomparison (Tables 1–3).
The boron content in pseudosinhalite was semiquantitatively determined with sinhalite from Johnsburg,
New York, as a “standard”. Sinhalite-containing grains
were embedded within a thin section of sample ST24
to avoid polishing effects and variable thicknessesof carbon coating. A probe current of 20 nA and a
LSM 200 multilayer analyzing crystal were used.
The boron content was calculated by comparison of

background-corrected peak-count rates on sinhalite andpseudosinhalite.
The content of beryllium and of selected traceelements was determined by laser-ablation – inductively
coupled plasma – mass spectrometry (LA–ICP–MS)(laser-ablation unit: New Wave UP 213; ICP–MS:
Agilent 7500) at the Institut für Chemie, Karl-FranzensUniversität Graz. Material was ablated by using a 213
nm laser pulsed at 5 Hz, 40 mm spot size and 70% laser
power, which corresponds to an energy of ~8 J/cm2.
Helium was used as carrier gas at ca. 1.2 L/min flow
rate, and data were acquired in time-resolved mode. The
standard glasses NIST610, NIST612, and BCR–2 wereroutinely analyzed for calibration and drift correction.
Aluminum was used as internal standard.
To obtain a X-ray powder pattern of pseudosinhalite,
chips of sample ST24 were treated with formic acid, andgrains and aggregates apparently rich in pseudosinhalite
were hand picked from the insoluble material. A partof the separated grains was ground, whereas anotherpart was embedded in epoxy resin and polished. The
X-ray pattern was recorded with a Siemens D5000
diffractometer at the Institut für Erdwissenschaften,
Karl-Franzens-Universität Graz, operating with CuKa
radiation and twin Goebel-mirror X-ray optics. The
reflections were measured from 15° to 70° 2u with astep size of 0.02° and a counting time of 15 seconds
per step. Unit-cell parameters for pseudosinhalite were
calculated with the program Topas Version 3.0 (Bruker
AXS 2003) using fundamental parameters for peakrefinements.

Occurrence and Petrography
Pseudosinhalite was discovered in an abandoned
quarry located ca. 1 km west of Stubenberg am See,
Styria, Austria (47°14’38”N, 15°47’15”E). This quarry
exposes polymetamorphic rocks of the Austroalpine
Strallegg Complex (Schuster et al. 2001). Partly
migmatized paragneisses and micaschists are dominant,whereas amphibolites, “leucophyllites” (muscovite– clinochlore – quartz phyllonites) and a leucocratic,
Permian granite gneiss (“Stubenberg granite”) are
subordinate. The formerly abundant granite gneiss
was mainly used for road construction, but it is now
almost totally quarried out. Dolomite marbles andforsterite–calcite marbles occur with pegmatites andamphibolites in a steeply plunging zone ca. 10 m wide
within the paragneisses and micaschists. In contrast
to the latter, the marble-rich zone and its immediately
adjoining rocks are not penetratively deformed; instead,deformation is mostly restricted to anastomosing shearbands and faults. Various metasomatic features can beobserved, such as the formation of wollastonite skarn
between marble and amphibolite.
Pressure–temperature conditions for the Permian
contact metamorphism around the Stubenberg granite
are assumed to be 500–600°C and 0.2 GPa (Tropperpseudosinhalite after spinel in marble from styria

et al. 2007). Eo-Alpine metamorphic conditions are
estimated from metamorphic assemblages in the granite
gneiss, paragneisses and micaschists to be in the range
of 530–600°C and 1.2–1.5 GPa (Tropper et al. 2007).
Pseudosinhalite was found in two loose blocks ofmarble (ST23 and ST24) with veins rich in geikielite–
ilmenite – baddeleyite – zirconolite, one of them (ST24)
containing also the magnesiotaaffeite minerals. The
two blocks seem to come from different parts of themarble-rich zone, and their appearance and mineralogy
are slightly different; therefore they are described separately. In contrast to the veins studied by Tropper et al.
(2007), neither sample shows any metasomatic zoning
around the Ti–Zr-rich veins.
Block ST23
This block of white dolomite marble contains
spots and streaks of yellowish to greenish forsterite– clinochlore – calcite marble with some Ti-bearing
clinohumite. A black, partly massive vein of Fe-richgeikielite up to several mm thick is located mostly

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within the dolomite marble and oriented more or lessparallel to the silicate-rich marble layers (Fig. 1a). In
reflected light, the geikielite appears granular withstraight grain-boundaries and 120° triple junctions.
Subordinate amounts of apatite-(CaF), dolomite, calcite,
zirconolite and baddeleyite also are present. Pink tolilac, anhedral to euhedral crystals of spinel occur
locally, mostly at the contact between the geikielite
vein and the dolomite marble. The spinel crystals are
partly euhedral with straight boundaries against carbonates (Fig. 2a). Pinkish grey to dull lilac-grey granularaggregates up to 2 mm across are rich in pseudosinhalite
and have partly or completely replaced spinel. Besides
spinel relics, abundant inclusions of calcite also arepresent (Figs. 1b, c, d, 2b). The typical size of individual
crystals of pseudosinhalite is 5–50 mm. Pseudosinhalite
is generally partly or totally replaced by clinochlore(Fig. 2b) with abundant micrometric inclusions of
Cr-rich spinel or magnesiochromite. This clinochlore
is brownish in hand specimen and more abundant thanspinel or pseudosinhalite.

Fig. 1. Sample ST23. a) Polished slab of white dolomite marble with a black, horizontal vein of geikielite and spots and streaksof yellowish to greenish forsterite – clinochlore – calcite marble. Red ellipse denotes an area rich in pseudosinhalite. b)
Broken surface of pseudosinhalite-rich aggregates (pinkish grey) with white carbonates and black geikielite. c) Thin section
photograph showing aggregates of pseudosinhalite with a small relic of spinel in carbonates. Plane-polarized light. d) Sameas c), crossed polarizers.

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Fig. 2. Back-scattered-electron (BSE) images of pseudosinhalite and magnesiotaaffeite minerals from Stubenberg. a) Pseudo­sinhalite with abundant relict spinel and calcite inclusions is partly replacing spinel. At the upper right, zoned spinel shows
straight grain-boundaries with dolomite. Sample ST23. b) Pseudosinhalite replacing spinel, which retains some original
chemical zoning. Note the abundant relics of spinel as well as calcite inclusions in pseudosinhalite and the replacement byclinochlore, slightly brighter than pseudosinhalite. At the upper left, pseudosinhalite occurs at grain boundaries of carbonates. Sample ST23. c) Pseudosinhalite and magnesiotaaffeite-6N’3S are replacing spinel. Magnesiotaaffeite-6N’3S contains
inclusions of pseudosinhalite, and is Zn-rich (bright) where it directly replaces spinel. Sample ST24. d) Large crystal ofmagnesiotaaffeite-6N’3S with inclusions of spinel and pseudosinhalite. Sample ST24. e) High-contrast BSE image of anaggregate of pseudosinhalite crystals with inclusions of spinel and calcite (white spots). Sample ST23. f) Magnesiotaaffeite6N’3S with a central lamella of magnesiotaaffeite-2N’2S. Sample ST24. Abbreviations: Ps: pseudosinhalite; Mgt: magnesiotaaffeite minerals; G: geikielite; Zirc: zirconolite; other abbreviations after Kretz (1983).

pseudosinhalite after spinel in marble from styria

Block ST24
This block consists of light grey dolomite marble
with fine-grained bands of dolomite – diopside –phlogopite marble. A black vein, approximately 1
cm thick runs parallel to this banding and consistsof Mg-rich ilmenite, calcite and dolomite in roughly
equal proportions and lesser amounts of apatite(CaF), secondary clinochlore, spinel, pseudosinhalite,
magnesiotaaffeite minerals, baddeleyite, zirconolite(commonly with a baddeleyite core) and rutile. In a very
few cases, spinel and magnesiotaaffeite-6N’3S enclose
grains of zirconolite. Ilmenite, carbonates, apatite andspinel have mostly straight grain-boundaries. Spinel
is most commonly fresh, but has been in places partly
replaced by granular aggregates rich in pseudosinhalite(Fig. 2c). Individual crystals of pseudosinhalite are up
to 50 mm across and contain abundant inclusions ofspinel and calcite. Magnesiotaaffeite-6N’3S overgrows
both spinel and pseudosinhalite and forms relatively
large laths up to 0.3 mm long (Figs. 2c, d). Late-stage
clinochlore replaces pseudosinhalite, spinel and, insome cases, magnesiotaaffeite-6N’3S.

Mineral Compositions
SpinelThe primary spinel has a similar composition in both
samples and is continuously zoned. The core contains
more than 90 mol.% of the spinel component, about

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5 mol.% of the hercynite component, and subordinate
amounts of Cr, V and Zn (Table 1). The rim is variably
enriched in Zn, with a mean value of 12 mol.% of thegahnite component, and up to 18 mol.% in individual
spots. The spinel inclusions in pseudosinhalite andmagnesiotaaffeite-6N’3S have a similar composition tothat of the spinel rims (Table 1).
Pseudosinhalite
There is no significant difference in composition
between the two samples. Fifty-two analyses, 18 insample ST23 and 34 in sample ST24, yielded a mean
analytical total of 74.81 wt.%, which is coincidentallythe same as the theoretical total calculated from theideal formula Mg 2Al 3O(BO4) 2(OH). High-contrast
BSE images show a patchy distribution of brightness, with bright spots enriched in Ti and, to a lesser
degree, Cr (Fig. 2e). Elements with Z > 8 found by
quantitative analyses are Al (45.2–49.4 wt.% Al2O3),
Mg (23.8–25.1% MgO), Ti (0.13–2.20% TiO2), Fe(0.65–1.28% FeO), Cr (<0.1–1.41% Cr2O3) and V(<0.1–0.48% V2O3) (Table 2); pseudosinhalite from
Stubenberg thus contains significant amounts of Ti, Cr
and some V, which were not reported in pseudosinhalite
from the type locality.
As pseudosinhalite represents a structural analogueof chondrodite (Strunz & Nickel 2000, Daniels &Schreyer 2001), the formula calculation is based on
five cations, ten atoms of oxygen, and two atomsof boron (Table 2). Iron was assumed to occur only

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as Fe2+. The calculated formula of the mean value
resulting from these analyses is: (Mg1.92Fe0.04)S1.96(Al2.96Ti0.05Cr0.02V0.01)S3.04O(BO4)2O0.09(OH)0.91.
Element–element correlation plots give a significant
negative correlation for Ti–Al and less significant negative correlations for the pairs V–Al and Cr–Al (Figs.
3a–c). Correlations between Mg and any other element
are not observed. This may be largely due to the relatively small variability in Mg content and the relatively
poor precision of the Mg analyses, blurring any significant trend. The correlation in Figure 3a suggests thatTi replaces Al in an approximate 1:2 ratio, suggesting asubstitution vector like Al–2(Mg,Fe)+1Ti+1. Considering
additional Cr and V gives an exchange vector of one Ti
atom for ca. 1.5 trivalent atoms (Fig. 3d).
WDX scans confirmed the presence of boron inpseudosinhalite, whereas comparatively scanned spinel,
magnesiotaaffeite-6N’3S and clinochlore gave no peak
for boron. Using sinhalite from Johnsburg, with a calculated boron content of 27.3 wt.% B2O3 as a “standard”(Table 2, Grew et al. 1991), resulted in a content of ca.
22.2% B2O3 for pseudosinhalite in sample ST24. Thisis very close to the theoretical value of 22.31% B2O3

calculated from the ideal formula, as well as the values
calculated from the analytical results from pseudo­sinhalite from Stubenberg (21.6–22.1%, Table 2) andof pseudosinhalite from the type locality (21.6–22.9%
B2O3, Schreyer et al. 1998). Boron contents of synthetic
material measured with the electron microprobe areslightly higher and vary between 23.3 and 24.3% B2O3
(Daniels et al. 1997).
Magnesiotaaffeite-6N’3S
and magnesiotaaffeite-2N’2S
These minerals were originally named “musgravite”
and “taaffeite”, respectively (Armbruster 2002).
Thirty-one analyses of magnesiotaaffeite-6N’3S insample ST24 yielded an analytical total of 94.52 wt.%,
which is slightly higher than the theoretical total of
93.92 wt.% (Table 3). Elements with Z > 8 found by
quantitative analysis are Al (69.2–73.7 wt.% Al2O3),
Mg (14.8–17.6% MgO), Zn (1.62–6.02% ZnO), Fe(1.70–2.44% FeO) and Cr (0.12–1.75% Cr2O3). The
calculation of the formula, based on Be = 1 atom per
formula unit (apfu), a total of 9 cations and 12 atoms

pseudosinhalite after spinel in marble from styriaof oxygen, gave for the mean value resulting from 31
analyses: Be1.00(Mg1.72Zn0.18Fe2+0.10)S2.00(Al5.93Cr0.04
Fe3+0.03)S6.00O12.
Zinc is strongly negatively correlated with Mg and,to a lesser degree, with Fe. Magnesium is weakly positively correlated with Fe. These observations suggestthat Zn replaces Mg as well as Fe via the simple substitution Zn(Mg,Fe)–1; they are in contrast to the findingsof Grew (2002), who noticed an increase of both Fe andZn at the expense of Mg. Typically, magnesiotaaffeite6N’3S is enriched in Zn where it replaces Zn-rich spinel(Fig. 2c). The content of Zn is roughly similar to thatreported from Antarctica, Greenland and France, but
far higher than in rough and faceted stones from Sri
Lanka (Schmetzer et al. 2005a). The zinc content inmagnesiotaaffeite-6N’3S from the type locality was notreported by Hudson et al. (1967). Our analyses confirm
that the mineral from the type locality is almost Zn-free,although with a very high content of Fe.
The Be content of the material from Stubenberg
measured by LA–ICP–MS differs only slightly fromthe theoretical value (Table 3). Magnesiotaaffeite-6N’3S
from the type locality, however, gave about 40% higher

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Be content than that measured by Hudson et al. (1967)
or the theoretical value. The amounts of MgO andFeO calculated from the LA–ICP–MS data are about
10% higher for both the material from Stubenberg andAustralia compared with SEM–EDX data. This is still in
the range of the accuracy of the LA–ICP–MS. We haveno explanation for the high Be values in material fromthe type locality. The variation in trace-element content
of three individual grains from Stubenberg are 10–20
ppm Li, 50–100 ppm Ti, 300–350 ppm V, 140–180 ppm
Mn, 40–60 ppm Co, 10–30 ppm Ni, and 300–400 ppm
Ga. The measured V, Mn and Ga contents were used in
the formula calculation (Table 3).
Magnesiotaaffeite-6N’3S crystals display in twocases bright zones in BSE images. These brightzones were analyzed, and their chemical composition
is consistent with magnesiotaaffeite-2N’2S, ideally
BeMg 3Al 8O 16 (Fig. 2f, Table 3). Calculation of aformula based on Be = 1 apfu, a total of 12 cations
and 16 atoms of oxygen gave for the mean resultof three analyses: Be 1.00(Mg 2.39Zn 0.46Fe 2+0.15) S3.00(Al7.95Cr0.03Fe3+0.02)S8.00O16.

Fig. 3. Plot of atoms per five cations (apfu) in pseudosinhalite from Stubenberg. Error bars represent 1s errors calculated fromcounting statistics of the EDX system. pts: polished thin section; pgm: polished grain mount; r: correlation coefficient oflinear fit; A: intercept; B: slope.

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The content of Zn is almost the same as in faceted
magnesiotaaffeite-2N’2S from Sri Lanka (Schmetzer et
al. 2005b), and considerably higher than those reported
from China and Russia (Schmetzer 1983).
According to Grew (2002), this is the first time thatboth magnesiotaaffeite minerals are found together. A
direct comparison between the two magnesiotaaffeite2N’2S lamellae and its hosting magnesiotaaffeite-6N’3S
crystals shows that the former is enriched in Zn bya factor of about 1.5 (ca. 6 wt.% versus ca. 4 wt.%
ZnO) and in total Fe by a factor of about 1.2. This is inagreement with the deductions of Grew (2002) basedon comparison of several occurrences of magnesiotaaffeite minerals. In contrast, chromium is depleted in one
magnesiotaaffeite-2N’2S lamella, whereas it is enrichedin the other compared to its host.
Other minerals
Iron-rich geikielite is the main mineral of Ti insample ST23. It is nearly homogeneous, with Mg/(Mg+ Fe + Mn) in the range 0.53–0.55. The most abundantTi-bearing mineral in sample ST24 is Mg-rich ilmenitewith Mg/(Mg + Fe + Mn) in the range 0.32–0.41.
The rim is enriched in iron compared to the core.
Clinochlore has Mg/(Mg + Fe) > 0.97 in both samples.
The crystal chemistry of zirconolite and baddeleyite
from Stubenberg is extensively discussed in Tropper
et al. (2007).

X-Ray Crystallography
Pseudosinhalite from Stubenberg is intimately intergrown with spinel, clinochlore, and calcite, and thus apure separate could not be prepared. The resulting X-ray
powder pattern includes reflections of these impurities,
as well as of quartz from the agate mortar (Fig. 4a).
Reflections of magnesiotaaffeite minerals were notobserved. The X-ray powder pattern was indexed on
the basis of the single-crystal structure refinement of
the synthetic phase (Daniels et al. 1997). Calculationof the monoclinic unit cell using whole-powder-pattern
fitting gave a 7.473(3), b 4.330(1), c 9.856(3) Å, b
110.72(2)°, V 298.3(3) Å3. In Table 4, we list measured
X-ray powder-diffraction data for pseudosinhalite from
Stubenberg, calculated powder data for the synthetic
phase Mg2Al3O(BO4)2(OH) with atom coordinates,
thermal parameters, and site occupancies taken from
Daniels et al. (1997), as well as powder data of pseudo­sinhalite from the type locality, Tayozhnoye, Siberia(Schreyer et al. 1998).
The cell parameters a and c and the cell volume ofnatural pseudosinhalite are somewhat larger than thoseof synthetic pseudosinhalite, which we suggest resultsfrom the partial substitution of Mg and Al by Fe, Ti, Cr
and V (Stubenberg) and Fe (Tayozhnoye). In contrast,
the cell parameter b is constant within error for all
three compositions of pseudosinhalite studied so far.

Discussion and Conclusions
Formation of spinel
Spinel is a rare mineral in marble at Stubenberg.
Typically, the marble contains clinochlore as the only
aluminous phase, both within the forsterite–calcite
marble as well as within the Ti–Zr-rich veins. Spinel insample ST24 locally overgrows zirconolite, suggestingthat the formation of zirconolite from baddeleyite
precedes or is at least coeval with the crystallization ofspinel. Tropper et al. (2007) attributed the formationof zirconolite to an increase of f(CO2) in the fluid. The
formation of spinel could be caused by a further increaseof f(CO2), leading to a breakdown of clinochlore.
The lack of any silicate phase (e.g., forsterite, quartz)
besides clinochlore suggests that Si was removed via
the fluid phase. A possible reaction could be:
Mg5Al(Si3Al)O10(OH)8 + 4 CaCO3 + 4 CO2 =   clinochlore       calcite
MgAl2O4 + 4 CaMg(CO3)2 + 3 SiO2, aq + 4 H2Ospinel     dolomite

pseudosinhalite after spinel in marble from styria

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Fig. 4. Observed X-ray powder pattern (CuKa radiation) of pseudosinhalite from Stubenberg (a) contaminated with spinel (Spl), clinochlore (Chl), calcite (Cal) and quartz (Qtz), and calculated powder pattern (b) for the synthetic phase
Mg2Al3O(BO4)2(OH) using results of the structure refinement reported by Daniels et al. (1997).

Formation of pseudosinhalite
Textural relations between pseudosinhalite andspinel, e.g., embayment of spinel by pseudosinhalite
and abundant relics of spinel enclosed in pseudosinhalite (Figs. 1c, d, 2a–c), provide clearcut evidence thatpseudosinhalite formed at the expense of spinel. In
addition, but to a lesser degree, pseudosinhalite seems
to have grown along grain boundaries between carbonates (Fig. 2b).
As pseudosinhalite is the only boron-bearing mineralin the mineral assemblage studied, its formation requires
influx of boron via a fluid phase. The Al/Mg ratio ofpseudosinhalite (ca. 1.5) is lower than that of the spinel(>2). This requires either addition of Mg to the site ofpseudosinhalite formation, or removal of Al. The former
is more likely, since Mg could be derived from dolomite
or geikielite breakdown or introduced by the boron-richfluid phase. In addition, as the spinel contains only
negligible amounts of Ti, this element has most likely
been added by breakdown of geikielite–ilmenite. The
minor elements Cr and V are in the same range ofconcentration in spinel and in pseudosinhalite, thus
no external source is required. Iron and zinc are muchhigher in spinel than in pseudosinhalite. A simplified
model reaction for the formation of pseudosinhalite
can be written as:
3 MgAl2O4 + CaMg(CO3)2 + 4 B(OH)3,aq =   spinel     dolomite
2 Mg2Al3O(BO4)2(OH) + CaCO3 + CO2 + 5 H2O   pseudosinhalite     calcite
The presence of abundant inclusions of calcite inpseudo­sinhalite is consistent with this reaction.
The Zn content of the spinel relics in pseudosinhalite
is similar to that in unaltered, Zn-rich rims of spinel
grains. The zinc content in unaltered spinel, however,is highly variable, and any trends might be obscured by
the original variability. The behavior of iron in spinelduring reaction progress is not totally clear. As Mg ispreferentially partitioned into pseudosinhalite, spinel
relics enclosed in pseudosinhalite should be enriched in
Fe compared to unaltered, large grains of spinel, whichhave a fairly uniform iron content (Table 1). However,this is not observed. The contribution of Mg from dolomite breakdown is not sufficient to increase the Mg/Fe
ratio of the pseudosinhalite to the values observed, even1204

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Daniels et al. (1997) suggested two possible modesof formation of pseudosinhalite: (1) as a retrograde
replacement product of sinhalite or (2) in amphibolitefacies and possibly lower-grade Mg–Al and B-richmetamorphic rocks of sedimentary or metasomaticorigin. Pseudosinhalite from the type locality belongs
to the first type. The occurrence at Stubenberg seems to
be of a third type of formation, because pseudosinhalite
is directly replacing a boron-free mineral (spinel) via
the interaction with a boron-rich fluid.
Formation of magnesiotaaffeite minerals
The magnesiotaaffeite minerals seem to have grownat the expense of pseudosinhalite and spinel. Theirbehavior concerning minor elements is quite different
from that of pseudosinhalite. They do not contain significant amounts of Ti, but Zn instead. Magnesiotaaffeite6N’3S is highly enriched in Zn where it replaces spinel(Fig. 2c). Its formation requires the introduction of Be
through a fluid phase, as there is no other mineral of Be
in the mineral assemblage.
Source of B and Be

if the dolomite is totally Fe-free. It is therefore likelythat Fe is largely removed by the fluid phase.
Pseudosinhalite can be considered as the lowtemperature equivalent of sinhalite. The equilibrium
pseudosinhalite = sinhalite + corundum + water islocated at ca. 700°C at 0.5 GPa and about 790°C at
1.5 GPa (Daniels et al. 1997). The occurrence of pseudosinhalite in the Stubenberg marble is consistent withthe experimental results. The conditions of the Permian
HT–LP event (500–600°C, 0.2 GPa), as well as those of
the overprinting Eo-Alpine metamorphism in the study
area (530–600°C, 1.2–1.5 GPa: Tropper et al. 2007) arewithin the stability field of pseudosinhalite.
Interestingly, dravite, which has a similar Al/Mg
value as pseudosinhalite, was not observed in themineral assemblage studied. Dravite would require theaddition of Si and Na by a fluid phase. This may indicate that the fluid introducing boron for pseudosinhalite
formation was very poor in Si and Na.

The Permian pegmatites within the Stubenberg
quarry contain abundant tourmaline as well as someberyl. Tourmaline (dravite) is also abundant withincorundum–margarite nodules, which locally occur atthe contact between pegmatites and forsterite–calcite
marble (Bernhard & Schachinger 2006). Texturalevidence suggests that the formation of baddeleyite
and zirconolite during Permian contact metamorphism(Tropper et al. 2007) preceded or was coeval withthe crystallization of spinel, which is the precursor of
B-bearing pseudosinhalite and Be-bearing magnesio­
taaffeite minerals.
From textural observations, it is not clear whether
the Mg–Al–(B,Be) oxides belong to the Permian
contact metamorphism or the Eo-Alpine metamorphic
overprint. In the first case, the crystallization of the
Mg–Al–(B,Be) oxides could be related to a late stageof contact metamorphism, promoted by the expelling ofmagmatic B- and Be-bearing fluids from the Stubenberg
granite or pegmatites. In the second case, Eo-Alpine
metamorphic fluids could have interacted with B- andBe-bearing lithologies, causing mobilization of B and
Be and formation of Mg–Al–(B,Be) oxides.
Alteration of Mg–Al minerals
The Mg–Al phases, especially pseudosinhalite,
are replaced at the latest stage by clinochlore. Thisrequires influx of SiO2,aq and the removal of boron,
as no other boron-mineral forms at the expense ofpseudosinhalite. Tropper et al. (2007) suggested anincrease of a(SiO2) causing the formation of zircon

pseudosinhalite after spinel in marble from styria

from baddeleyite and zirconolite during Permian contact
metamorphism. In samples ST23 and ST24, zircon was
not observed. Therefore, there is no textural evidence
that the formation of zircon and clinochlore is related
to the same SiO2-rich fluid. The alteration of Mg–Al
phases to clinochlore could have also occurred during
an Eo-Alpine metamorphic overprint, related to anotherSi-rich fluid.

Acknowledgements
We are indebted to Ed Grew and an anonymous
reviewer for their helpful and constructive commentson the manuscript, and Robert F. Martin for editorial
handling. The help and support of W. Gössler and C.
Kurta, Institut für Chemie, Karl-Franzens-Universität
Graz, during LA–ICP–MS analyses is gratefully
acknowledged.

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