Eur. J. Mineral.
2003, 15, 733-739

Graulichite-(Ce), a new arsenate mineral from the Stavelot Massif, Belgium
FRÉDÉRIC HATERT1,*, PIERRE LEFÈVRE1, MARCO PASERO2 and ANDRÉ-MATHIEU FRANSOLET1
1Laboratoire de Minéralogie, Université de Liège, B.18, B-4000 Liège, Belgium
2Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, I-56126 Pisa, Italy

Abstract: Graulichite-(Ce), ideally CeFe3+
3 (AsO4)2(OH)6, is a new mineral species from Hourt, Stavelot Massif, Belgium. It
occurs in the most altered parts of a Devillian quartzite (Lower to Middle Cambrian), in close association with arsenopyrite,
scorodite, mimetite, pharmacosiderite, and goethite. Graulichite-(Ce) forms 80 to 150 µm spherical aggregates of rhombohedral–––
crystals, 50 to 80 µm length, which show the forms {1012} and {101 1}. The mineral is transparent and exhibits a light-green tobrownish colour, with a resinous lustre. It is non-fluorescent and shows an irregular fracture, without any perceptible cleavage.
The calculated density is 4.42 g/cm3. Graulichite-(Ce) is uniaxial negative, with a mean refractive index close to 1.97(1)(l = 590 nm), pleochroic from light green to yellowish. Electron microprobe analyses gave As2O5 31.20, P2O5 0.03, SO3 0.06,
SiO2 0.03, Al2O3 3.09, Fe2O3 30.65, SrO 0.24, PbO 0.07, BaO 3.95, CaO 0.03, La2O3 2.26, Ce2O3 15.73, Nd2O3 2.08, H2O (calc.)
8.37, total 97.79 wt. %. The resulting empirical formula, calculated on the basis of 6 cations, is (Ce0.67Ba0.18La0.10Nd0.09Sr0.02)S1.06(Fe3+
2.68Al 0.42)S3.10[(As1.89S0.01 0.10)S2.00O8][(OH)5.57(H2O)0.43]S6.00. The single-crystal unit-cell parameters are a = 7.288(2) andc = 16.812(9) Å, space group R3–m. The seven strongest lines in the X-ray powder-diffraction pattern [d(in Å)(I)(hkil)] are:–3), 3.636(40)(112–0), 2.239(35)(101–7), 1.817(35)(224–0), 2.792(30)(0006), 5.906(25)(101–1), 1.968(25)(303–3).
3.052(100)(112
Graulichite-(Ce) is the iron analogue of arsenoflorencite-(Ce), and belongs to the crandallite mineral group, with the alunite-type
structure. The crystal structure of graulichite-(Ce) has been refined, based on single-crystal X-ray diffraction data, to R = 0.048.
Key-words: Graulichite-(Ce), new arsenate mineral, REE, crandallite group, Hourt, Stavelot Massif, Belgium, crystal structure.

Introduction
In the southeastern border of the Stavelot Massif,
Belgian Ardennes, the metapelites belonging to therecently defined stratigraphic Salm Group (Verniers et al.,2001) of Cambro-Ordovician age are cross-cut by
numerous quartz veins which host, among others, relatively
rare Mn-rich aluminosilicates which crystallised during a
low-grade metamorphism of Hercynian age (Schreyer,1975). Besides the occurrence of these minerals, the presence of sulphides in the quartz veins is known for a longtime (Hatert et al., 2002). During the last decade, thesesulphides have been carefully reinvestigated (Hatert, 1996;
Hatert, submitted), as well as their oxidation and alteration
products (Hatert et al., 1998).
These mineralogical studies reveal the presence ofarsenopyrite (Hatert, 1997), particularly as new occurrences in rocks of other stratigraphic position, like rocks of
the Deville and Revin Groups (Verniers et al., 2001).
Recently, Hanson et al. (1999) discovered the associationof gold and arsenopyrite in the quarry of Hourt, in rocks of
the Deville Group. This description prompted us to investi-

gate the new occurrence of arsenopyrite and to study themineralogical association of this quarry (Lefèvre, 2001;
Lefèvre & Hatert, in press).
Among the secondary minerals associated witharsenopyrite from Hourt, collected by S. Puccio, M.
Blondieau, J. Detaille and J. Dehove, brown to greenish
coatings, constituted by well-developed rhombohedral crystals, were identified as a mineral of the crandallite group.
The preliminary chemical analyses performed by one of us(F.H.) indicated that this mineral probably corresponds to
the Fe3+-rich equivalent of arsenoflorencite, (Ce,La)Al3(AsO4,PO4)2(OH)6, not yet described. The detailed study ofthis species by Lefèvre (2001) confirmed the existence ofa new mineral species, which was approved by theCommission on New Minerals and Mineral Names of theInternational Mineralogical Association (no. 2002-001)
under the name graulichite-(Ce). The mineral is named inhonour of Jean-Marie Graulich (1920-2001), mining engineer and honorary Director of the Geological Survey of
Belgium, particularly for his contribution to the geology of
the Stavelot Massif. The holotype is stored in the collectionof the Laboratory of Mineralogy, University of Liège,*E-mail: fhatert@ulg.ac.be

DOI: 10.1127/0935-1221/2003/0015-0733

0935-1221/03/0015-0733 $ 3.15
© 2003 E. Schweizerbart’sche Verlagsbuchhandlung. D-70176 Stuttgart

734

F. Hatert, P. Lefèvre, M. Pasero, A.-M. Fransolet

Fig. 1. Scanning electron microscope photograph of graulichite(Ce) from Hourt. The mineral forms spherical crystal aggregates or–
isolated {1012} rhombohedra, lying on a goethite coating.

Belgium (no. 20325) and in the collection of the Royal
Belgian Institute of Natural Sciences, Brussels (no. RN6419).

Geological setting
Graulichite-(Ce) has been discovered in the quartzites
mined in the quarry of Hourt, 2 km north of Vielsalm, inthe southeastern border region of the Stavelot Massif.
Geologically, the Stavelot Massif constitutes an exposedpart of the Caledonian basement situated near the northwestern border of the Hercynian Rhenish Massif. The
whitish quartzites from Hourt are of Cambrian age andstratigraphically belong to the Deville Group (Verniers etal., 2001). The area of Hourt is extremely tectonised, witha lot of faults and folds, and was affected by two orogenic
phases, a Caledonian and an Hercynian one (Bless et al.,1990). The study of fluid inclusions, observed in quartz
pebbles by Ferket et al. (1998) and Schroyen & Muchez(2000), indicates that pressure and temperature conditions
close to 3 kbar and 380°C have probably been reachedduring the first Caledonian orogenic phase. In the region of
Salmchâteau-Ottré-Lierneux, Kramm (1982) and Krammet al. (1985) estimated the metamorphic conditions
prevailing during the Hercynian phase to about 360-420°C
and ~ 2 kbar, as indicated by both the presence of
andalusite and the paragonite content of muscovite.

Physical properties
Graulichite-(Ce) has been found in the most alteredparts of the quartzite of Hourt, where it is associated witharsenopyrite, scorodite, mimetite, pharmacosiderite,
barium-pharmacosiderite and goethite (Lefèvre, 2001;
Lefèvre & Hatert, in press). The mineral occurs as spher-Fig. 2. Morphology of graulichite-(Ce) from Hourt, showing the–––
combination {1012}{101 1}.

ical aggregates, 80 to 150 µm in diameter, constituted byrhombohedral crystals, 50 to 80 µm length (Fig. 1).
Goniometric measurements, performed on isolated crystals–
reaching 50 µm length, indicate the presence of the {1012}––
rhombohedron, associated with smaller {101 1} faces(Fig. 2).
Graulichite-(Ce) is transparent and exhibits a lightgreen to brownish colour, with a resinous lustre. The
mineral is non-fluorescent and shows an irregular fracture,
without any perceptible cleavage. The density exceeds
3.9 g/cm3, because the crystals sink in diluted Clerici solution. The calculated density, based on the empiricalformula, is 4.42 g/cm3. Under the polarising microscope,crystals are uniaxial negative, with a mean refractive index
close to 1.97(1) (l = 590 nm). Pleochroism is from lightgreen to yellowish. Birefringence is difficult to estimate,because the interference colours are masked by the green
colour of the mineral.

Chemical composition
Quantitative chemical analyses were performed on
isolated crystals with a Cameca SX-50 electron microprobe(CAMST, Louvain-la-Neuve, Belgium) operating in the
wavelength-dispersion mode, with an accelerating voltage
of 20 kV and a beam current of 20 nA. The following standards were used: corundum (Al), fayalite (Si, Fe), barite (S,Ba), strontianite (Sr), apatite (P), synthetic wulfenite (Pb),wollastonite (Ca), pure metal (As), and synthetic glasses(Ce, La, and Nd).
As graulichite-(Ce) belongs to the crandallite group,
according to its X-ray powder diffraction pattern, thechemical formula of this mineral was calculated on thebasis of 6 cations (Table 1). As already observed for otherminerals of the crandallite group (Hanson, 1983 ; Nickel &Temperly, 1987), a deficit of As occurs on the tetrahedral

Graulichite-(Ce), a new arsenate mineral
Table 1. Electron-microprobe analyses of graulichite-(Ce) from
Hourt.
1
2
As2O 531.20 (0.58)
1.893
P2O 5
0.03 (0.04)
0.003
SO 3
0.06 (0.05)
0.005
SiO2
0.03 (0.02)
0.004
Al2O 33.09 (1.41)
0.423
Fe2O 330.65 (2.16)
2.676
SrO
0.24 (0.10)
0.016
PbO
0.07 (0.07)
0.002
BaO
3.95 (0.82)
0.180
CaO
0.03 (0.03)
0.004
La2O 32.26 (0.67)
0.097
Ce2O 315.73 (0.87)
0.668
Nd2O3
2.08 (0.47)
0.086
H 2O (*)
8.37
6.425
Total
97.79
Analyst : J. Wautier. 1: Average of 33 analyses (in wt.
%, with s given in parentheses). 2: Number of cations
based on 6 cations per formula unit. *: calculated
value based on 6(OH,H2O) per formula unit.

site of the structure. Because V was not detected qualitatively by SEM-EDS, and because P and Si are only present
in very small amounts (Table 1), we suspect the occurrenceof vacancies in this crystallographic site. The large cationicsite of the structure contains Ce, La, Nd and Ba as major
cations, whereas Fe3+ and subordinate Al occupy the octahedral site.
The substitution of REE3+ by Ba2+ on the large cationicsite implies an excess of negative charges, which iscompensated by the replacement of (OH)- groups by H2O.
This substitution mechanism has already been observed byKolitsch et al. (1999) in dussertite, BaFe3+
3 (AsO4 )2(OH,H2O)6. The empirical formula of graulichite-(Ce), deduced from the microprobe analyses (Table 1), corresponds
to (Ce0.66 Ba0.18 La0.10Nd 0.09 Sr0.02)S1.06 (Fe3+
2.68Al 0.42) S3.10[(As1.89S0.01 0.10)S2.00O8][(OH)5.57(H2O)0.43]S6.00.

X-ray powder diffraction
The X-ray powder-diffraction pattern of graulichite(Ce), given in Table 2, was recorded on a PHILIPS PW3710 diffractometer using FeKa radiation (l = 1.9373 Å).
This powder pattern is similar to those of arsenate membersof the crandallite group. On the basis of the d-spacings
shown in Table 2, which were calibrated with an internal
standard of quartz, the least-squares refinement program
LCLSQ 8.4 (Burnham, 1991) has served to calculate theunit-cell parameters in an hexagonal orientation. The celldimensions obtained are a = 7.260(5) and c = 16.77(2) Å.

Structure refinement
Several crystals of graulichite-(Ce) were preliminarily
tested by rotation and Weissenberg methods. The unit cell

735

Table 2. Indexed X-ray powder-diffraction pattern of graulichite(Ce).
Iobs.
dobs.(Å)
dcalc.(Å)
hkil
–
25
5.906
5.887
1011
–
40
3.636
3.630
1120
–
10
3.088
3.090
2021
–
100
3.052
3.044
1123
30
2.792
2.794
0006
–
10
2.519
2.515
2024
–
35
2.239
2.238
1017
–
25
1.968
1.962
3033
–
35
1.817
1.815
2240
–
15
1.681
1.687
2137
–
10
1.543
1.545
4042
–
10
1.481
1.479
2 0 2 10
–
5
1.371
1.372
4150

metrics, the Laue symmetry and the systematic absences,
as well as the crystal morphology, were consistent with the––space groups R3m, R32 and R3. By analogy with otherminerals of the crandallite group (Jambor, 1999), the space–group R3m was inferred.
Single crystals of graulichite-(Ce) always consist of
several subparallel individuals, and show a powder-likepattern, with diffuse streaks on which only weak and badshaped reflection spots are superimposed. We crushedsome of them aiming to obtain a crystal fragment suitablefor intensity data measurements, and a very small fragment
was eventually brought to the Elettra synchrotron laboratory. The high energy of the synchrotron radiation raised
the brightness of the diffraction spots, however, it caused
the enhancement of the powder-like effect as well. As aconsequence, the procedure of indexing of the reflection
spots frames recorded with a CCD detector failed.
Therefore, the structural study was carried out on aconventional four-circle diffractometer, using a small
crystal fragment which apparently showed a good degree ofcrystallinity and an only small tendency for subparallelintergrowth. The overall low intensity of the reflections
prevented us to obtain a reliable set of y-scan data for anempirical absorption correction. For that reason, despite
the higher point group symmetry, a whole sphere of reflections was measured. In such a way, as a partial compensation for the lack of absorption correction, we got a set ofindependent squared amplitudes, each resulting from averaging several equivalent measurements. We also tried asemi-empirical treatment of absorption effects with theprogram MULTISCAN included in the WinGX package(Farrugia, 1999), which performs an absorption correction
based upon the Blessing algorithm (Blessing, 1995).
However, this did not result in any significant improvementof the model, and was eventually left out.
The refinement was started using the atomic coordinates of florencite (Kato, 1990) and setting cation occupancies in keeping with the chemical composition ofgraulichite-(Ce). For the sake of simplicity, Ce only was
allocated to the large interlayer site, since its atomic
number (58) was quite close to the average atomic number(57.4) resulting from the chemical analysis. Then, the occu-

736

F. Hatert, P. Lefèvre, M. Pasero, A.-M. Fransolet
Table 3. Experimental details for the single-crystal X-ray diffraction study of graulichite-(Ce).
Dimensions of the crystal (mm)Unit-cell parameters (Å)
Space group
Diffractometer
Operating conditions
Radiation
Scan mode
Scan width (in q)
Scan speed
2qmax
Range of indicesMeasured intensities
Independent non-zero [Fo > 4s(Fo)] reflections
Absorption correction
l.s. refinement program
Refined parameters
R (on F’s)
Rw (on squared F’s)
S (goodness of fit)
Max D/s in the last l.s. cycle
Max peak and hole in the final DF map (e/Å3)

pancy of Fe3+ against Al was refined in the octahedral site,
and the occupancy of As against vacancy was refined in thetetrahedral site. The refinement was completed using
anisotropic displacement parameters for all atoms. The
final conventional R factor was 0.0475. Further details of
the intensity data collection and refinement are given in
Table 3.

Table 4a. Final fractional coordinates and equivalent isotropic
displacement parameters (Å2) for graulichite-(Ce).
Atom
x
y
z
U eq
Ce
0
0
0
0.0269(10)
Fe*
0.5
0.5
0.5
0.0158(11)As**000.3168(2)0.0174(12)O1000.416(1)0.024(5)O20.2076(10) -0.2076(10) -0.0512(7)0.027(3)OH
0.1244(9)-0.1244(9)0.1328(7)0.026(3)* Refined site occupancy: Fe 83.0(7)% + Al 17.0(7)%** Refined site occupancy: As 92.4(3)% + 7.6(3)%ca. 0.05 x 0.04 x 0.03
a 7.288(2), c 16.812(9)–R3m
Siemens
50 kV, 40 mA
MoKa (l = 0.71069 Å)
q-2q
±0.6°
1°/min50°-8 £ h £ 8, -8 £ k £ 8, -19 £ l £ 19
1720
151
None
SHELXL-93 (Sheldrick, 1993)
27
0.04750.12461.124
0.000+1.97 and –1.23

Discussion
Compatibility
The compatibility of graulichite-(Ce) is calculated withthe relationship proposed by Mandarino (1981). Because
no accurate density measurements are available, the calculations were performed with the calculated density of
4.42 g/cm3. The compatibility index, 1-(KP/KC), is equal to0.005, thus indicating a superior compatibility.
Structural features
Final positional and displacement parameters forgraulichite-(Ce) are given in Table 4, whereas selectedbond distances are given in Table 5. The greatest rmax/rmin
ratio between axes of the displacement ellipsoids is 2.76 for
the Ce site.
The basic features of the structure of graulichite-(Ce)are identical to those of the other members of the alunitecrandallite structure-type, therefore they will not be
considered in detail here. It is just worth noting that theTable 4b. Anisotropic displacement parameters for graulichite-(Ce).
Atom

U11

U22

U 33

U 23

U 13

U12

Ce
Fe
As
O1
O2
OH

0.034(1)0.020(2)0.021(1)0.027(7)0.032(5)0.020(5)0.034(1)0.020(2)0.021(1)0.027(7)0.032(5)0.020(5)0.012(1)0.010(2)0.011(2)0.017(10)0.021(6)0.037(7)0-0.0012(7)000.001(3)-0.003(3)00.0012(7)00-0.001(3)0.003(3)0.0171(6)0.011(2)0.0104(7)0.014(3)0.019(6)0.010(5)Graulichite-(Ce), a new arsenate mineral

737

Table 5. Selected bond distances (Å) for graulichite-(Ce).
Ce-OH (x6)Ce-O2 (x6)<Ce-O>

2.731(12)2.758(12)2.74

Fe-OH (x4)
Fe-O2 (x2)<Fe-O>

1.978(5)2.010(11)
1.99

As-O1
As-O2 (x3)<As-O>

1.660(19)1.690(12)1.68

Table 6. Site occupancies and mean cation-oxygen distances (Å) in some minerals of the crandallite group.
Mineral
XII-coordinated site
VI-coordinated site
IV-coordinated site
Crandallite1
Ca
2.711
Al
1.902
P
1.537
Gorceixite2
Ba
2.847
Al
1.901
P
1.533
Goyazite3
Sr
2.748
Al
1.896
P
1.535
Florencite4
Ce
2.681
Al
1.893
P
1.546
Kintoreite5
Pb
2.859
Fe
2.011
P0.73As0.16S0.11 1.563
Dussertite6
Ba
2.874
Fe0.84Sb0.16 2.009
As
1.684
Graulichite-(Ce)7Ce
2.74
Fe0.83Al0.17 1.99
As0.92 0.08 1.68
1. Blount (1974); 2. Radoslovich (1982); 3. Kato (1987); 4. Kato (1990); 5. Kharisun et al. (1997); 6. Kolitsch
et al. (1999) ; 7. This study.

Table 7. Comparison of graulichite-(Ce) with other arsenate minerals of the crandallite group.
Mineral nameChemical formulaSpace group a (Å)

Graulichite-(Ce)1
Dussertite2,3,4Segnitite5
Arsenogorceixite6
Arsenocrandallite6
Arsenogoyazite7
Philipsbornite8
Arsenoflorencite-(Ce)9

CeFe3(AsO4)2(OH)6
BaFe3(AsO4)2(OH,H 2O)6
PbFe3(AsO4)2(OH,H 2O)6
BaAl3(AsO4)2(OH,H2O)6
CaAl3(AsO4)2(OH,H2O)6
SrAl3(AsO4)2(OH,H2O)6
PbAl3(AsO4)2(OH,H2O)6
CeAl3(AsO4)2(OH)6

–
R3m
–
R3m
–
R3m
–
R3m
–
R3m or R3m–
R3m or R3m–
R3m or R3m
–
R3m

c (Å)

Refractive index

Optical Dmeas
Dcalc
sign
(g/cm3) (g/cm3)

7.260(5) 16.77(2) 1.97(1)U> 3.94.42
7.410(3) 17.484(4) w=1.87 e=1.85 U3.75
4.293
7.359(3) 17.11(8) w=1.975 e=1.955 U> 4.2
4.77(1)7.10(2) 17.39(4) n.g.
n.g.
n.g.
n.g.
7.08
17.27
1.625(10)n.g.
3.25(1) 3.30
7.10
17.16
1.64(3)n.g.
3.35(5) 3.65
7.11
17.05
1.790(3)n.g.
> 4.10 4.33
w=1.739 e=1.745 U+
7.03
16.517
4.10
4.09
1. This study ; 2. Barthoux (1925) ; 3. Walenta (1966) ; 4. Kolitsch et al. (1999) ; 5. Birch et al. (1992) ; 6. Walenta (1981) ; 7. Walenta& Dunn (1984) ; 8. Walenta et al. (1982) ; 9. Nickel & Temperly (1987). n.g. : not given.

average bond distances (Table 5) are in fairly good agreement with the cation site occupancies, and the latter match
well the chemical composition of graulichite-(Ce).
A number of structure refinements are available forminerals of the alunite- and the crandallite-type. In Table 6
the mean cation-oxygen distances in some crandallite
subgroup minerals are compared.
Graulichite-(Ce) in the crandallite mineral group
Electron microprobe analyses (Table 1) indicate thatgraulichite-(Ce) is the Fe3+-rich analogue of arsenoflorencite-(Ce). The nomenclature of the crandallite group has
recently been revisited by Jambor (1999). Comparisons of
the physical properties of graulichite-(Ce) and those ofother arsenate minerals of this group are given in Table 7.
As shown in Fig. 3, the chemical data of the graulichite(Ce) crystals from the Hourt quarry are clearly localised in
the Ce-rich part of the Ce-La-Nd diagram. For this reason,
and according to the nomenclature proposed by Jambor(1999) for minerals of the crandallite group, the mineral isnamed graulichite-(Ce). “Graulichite-(La)” and “graulichite-(Nd)” are hypothetical end-members.

Fig. 3. Results of electron microprobe analyses of graulichite-(Ce),plotted in the Ce-La-Nd diagram. *: “Graulichite-(La)” and“graulichite-(Nd)” are the hypothetical La- and Nd- analogues ofgraulichite-(Ce).

738

F. Hatert, P. Lefèvre, M. Pasero, A.-M. Fransolet

Genesis of graulichite-(Ce)All the arsenate minerals occurring in the quarry ofHourt, including graulichite-(Ce), derive from the oxydation of arsenopyrite. Indeed, these secondary minerals crystallise in small cavities produced by the leaching ofarsenopyrite. Graulichite-(Ce) contains signif icant
amounts of Ba in the A site of the alunite-type structure. It
is noteworthy that Lefèvre (2001) described barium-pharmacosiderite, BaFe3+
8 (AsO4)6(OH)8.14H 2O, in very close
association with the new mineral species. Although no
geochemical data are available up to now for the enclosing
rocks of the Deville Group, the presence of Ba is known as
major element in hollandite (Schreyer et al., 2001) or in
Ba-rich mica (Kramm, 1980; Schreyer et al., 2001) inrocks of the Salm Group from Vielsalm and Salmchâteau,
whereas florencite-(Ce) was detected in the same area
(Theunissen & Martin, 1969; Hanson, 1983). It can beassumed that these particular elements (REE, Ba) wereleached during the intense alteration undergone by thewhole Stavelot Massif during the tropical climate of the
Tertiary period (Alexandre & Thorez, 1995). As theminerals of the crandallite group with prevailing Al and Fe
are able to easily stabilise elements such as Ba and REE(Kolitsch & Pring, 2001), the formation of graulichite-(Ce)and of the associated arsenates from Hourt can be
attributed to Tertiary processes of weathering.
Acknowledgements: Many thanks are due to Prof. H.
Effenberger and to Dr. U. Kolitsch, for their careful reading
and critical comments of the first version of thismanuscript, as well as to M. Blondieau, J. Dehove, J.
Detaille and S. Puccio, who collected and gave us somesamples from the Hourt quarry.

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Received 16 December 2002
Modified version received 7 January 2003
Accepted 18 March 2003