![suggest a [4] B content of ~0.01-0.02 apfu. The remaining spectra indicate that neither [4] Al nor [4] B is present in quantities detectable by MAS NMR in this crystal. Ultrahigh-field NMR (21.1 T) and ultrafast MAS (62 kHz) were used in conjunction on one sample to reduce the second-order quadrupolar broadening and minimize any paramagnetic interactions. The [6] Al peak narrowed by a factor of 2 in ppm relative to the 14.1 T data, thereby increasing the spectral resolution and verifying that no [4] Al signal is evident (data not shown). A requirement for MAS NMR spectroscopy is that the sample under investigation be low in paramagnetic constituents (e.g., Fe 2+ , Mn 2+ ). In a detailed study of 11 B and 27 Al MAS NMR spectra collected on 50 different samples of tourmaline, Lussier et al. (2009) showed that in samples with extremely low contents of paramagnetic ions (Fe 2+ + Mn 2+ < 0.05 apfu), [4] B and [4] Al signals are easily resolved by MAS NMR, but the presence of greater than ~0.1 apfu transition metals may degrade the spectrum considerably through signal broadening, thereby increasing the limit of detection of tetrahedrally coordinated species.](https://www.researchgate.net/profile/Frank-Hawthorne/publication/233978199/figure/fig2/AS:668998911946770@1536513178885/suggest-a-4-B-content-of-001-002-apfu-The-remaining-spectra-indicate-that-neither_Q320.jpg)
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63
The Canadian Mineralogist
Vol. 49, pp. 63-88 (2011)
DOI : 10.3749/canmin.49.1.63
OSCILLATORY ZONED LIDDICOATITE FROM ANJANABONOINA,
CENTRAL MADAGASCAR. I. CRYSTAL CHEMISTRY AND STRUCTURE BY SREF
AND 11B AND 27Al MAS NMR SPECTROSCOPY
AAron J. LUSSIEr, YASSIr ABDU AnD FrAnk C. HAWTHornE§
Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada
VLADImIr k. mICHAELIS, PEDro m. AGUIAr AnD SCoTT kroEkEr
Department of Chemistry, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada
ABSTrACT
The crystal structures of 23 samples extracted from a large slice oriented along (001) of a single crystal of liddicoatite
from the Anjanabonoina granitic pegmatite in Madagascar (showing pronounced, visually discontinuous oscillatory zones and
anomalous biaxiality) were rened to R1 indices of 1.5–2.9% (<R1> = 1.78%). Cell parameters are in the range a ≈ 15.82–15.87,
c ≈ 7.10–7.12 Å. Spindle-stage measurement of 2V gave values of 0.0° for a fragment from the (001) zone and 8(3) and 18.9(5)°
for fragments from the pyramidal zone of the crystal. However, single-crystal X-ray intensity data show no deviation from 3m
Laue symmetry, indicating that there is no information in the diffraction data on any deviation from R3m symmetry. The <T–O>
distances are in the range 1.616–1.619 Å, with a grand mean value of 1.6175(7) Å. The occupancy of the T site was expressed
as xSi + (1–x)B, and x was treated as variable in the renement procedure. The effect of using different scattering factors (i.e.,
ionized versus neutral) on the rened site-occupancies was investigated in detail. The grand mean rened [4]B content of the T
site varies from –0.04 apfu for ionized scattering-curves for O and Si to 0.25 apfu for neutral scattering-curves for O and Si,
illustrating the effect of the use of different scattering curves on rened [4]B site-populations. Examination of <T–O> distances as
a function of aggregate cation radius for tourmalines containing [4]B and [4]Al shows a large amount of scatter, emphasizing the
need for more accurate data. The limits of detection for 11B and 27Al in tourmaline by Magic-Angle-Spinning Nuclear Magnetic
Resonance (MAS NMR) spectroscopy were investigated by simulation. For minimum (<0.04 apfu) and maximum (0.12 apfu)
contents of (paramagnetic) transition metals, the limits of detection of [4]B are ~0.02 and 0.08 apfu, and of [4]Al are ~0.01 and
0.01 apfu, respectively. 11B and 27Al MAS NMR spectroscopy gave no evidence of the presence of tetrahedrally coordinated B
or Al at the T site above these detection limits in any sample. This result is in accord with our renement results using an ionized
scattering-curve for O and a neutral scattering-curve for Si, suggesting that use of these curves is giving more accurate results
than renement with neutral scattering factors. The <Z–O> distances are in the range 1.904–1.907 Å, with a grand mean value
of 1.9047(8) Å, and structure renement indicates site-scattering values in accord with complete occupancy of the Z site by Al.
Hence throughout this complexly zoned crystal, Si = 6.00 apfu and ZAl = 6.00 apfu.
Keywords: liddicoatite, elbaite, tourmaline, oscillatory zoning, crystal-structure renement, electron-microprobe analysis,
magic-angle-spinning nuclear magnetic resonance spectroscopy, Mössbauer spectroscopy, site populations, Anjanabonoina,
Madagascar.
SommAIrE
Nous décrivons la structure cristalline de 23 fragments extraits d’une section orientée le long de (001) d’un monocristal
de liddicoatite provenant de la pegmatite granitique d’Anjanabonoina, au Madagascar, et afnés jusqu’à un résidu R1 dans
l’intervalle 1.5–2.9% (<R1> = 1.78%). Ce cristal montre des zones oscillatoires discontinues et une biaxialité anomale. Les
paramètres réticulaires ont des valeurs dans les intervalles suivants: a ≈ 15.82–15.87, c ≈ 7.10–7.12 Å. Les mesures de 2V
utilisant ces fragments sur tige orientable ont donné des valeurs de 0.0° pour un fragment provenant de la zone (001), et 8(3)
et 18.9(5)° pour des fragments pris de la zone pyramidale. Toutefois, les données portant sur les intensités en diffraction X ne
révèlent aucune déviation de la symétrie de Laue 3m, ce qui montre qu’il n’y a aucune information concernant un écart de la
symétrie R3m dans ces données. Les distances <T–O> tombent dans l’intervalle 1.616–1.619 Å, avec une moyenne globale de
1.6175(7) Å. L’occupation du site T est exprimée sous forme xSi + (1–x)B, et nous avons traité x comme une variable au cours
des afnements. Le fait d’utiliser des facteurs de dispersion différents, c’est-à-dire des facteurs prévus pour des atomes neutres
§ E-mail address: frank_hawthorne@umanitoba.ca
64 THE CAnADIAn mInErALoGIST
ou des ions, exerce une inuence sur les occupations afnées des sites. La teneur moyenne globale en [4]B des sites T varie de
–0.04 apfu pour des facteurs d’atomes O et Si ionisés à 0.25 apfu en adoptant des facteurs de dispersion pour les atomes O et Si
neutres, illustration de l’importance de ces facteurs sur la quantité de [4]B qui est afnée. Un examen des distances <T–O> en
fonction des rayons regroupés des cations dans les tourmalines contenant [4]B et [4]Al montre de grands écarts, et démontre la
nécessité d’obtenir des données plus justes. Les limites de détection de 11B et 27Al dans une tourmaline par résonance magnétique
nucléaire et spin à l’angle magique ont été étudiées avec des spectres simulés. Pour des teneurs minimales et maximales des
métaux de transition (paramagnétiques), <0.04 et 0.12 apfu, les limites de détection du [4]B seraient entre ~0.02 et 0.08 apfu, et
celles du [4]Al, entre ~0.01 et 0.01 apfu, respectivement. La spectroscopie MAS NMR des isotopes 11B et 27Al n’appuient donc pas
la présence de B ou Al en coordinence tétraédrique au delà du seuil de détection dans ces échantillons. Ces résultats concordent
avec nos afnement reposant sur des facteurs de dispersion, ionisé dans le cas de O et pour un atome neutre dans le cas de Si,
ce qui laisse croire que ce choix de courbes produit des résultats plus justes qu’un afnement avec seulement des facteurs pour
atomes neutres. Les distances <Z–O> tombent dans l’intervalle 1.904–1.907 Å, avec une moyenne globale de 1.9047(8) Å, et
l’afnement des structures indique des valeurs de dispersion aux sites en accord avec une occupation complète du site Z par Al.
C’est donc dire que dans ce cristal zoné de façon complexe, Si est égal à 6.00 apfu, ainsi que ZAl.
(Traduit par la Rédaction)
Mots-clés: liddicoatite, elbaïte, tourmaline, zonation oscillatoire, afnement de la structure cristalline, analyse avec une micro-
sonde électronique, résonance magnétique nucléaire avec spin à l’angle magique, spectroscopie de Mössbauer, populations
des sites, Anjanabonoina, Madagascar.
understanding (Hawthorne 1996, 2002, Pieczka 1999,
Bosi 2008, Bosi & Lucchesi 2007) of site occupancy
in tourmaline. Here, we characterize the compositional
and structural aspects of oscillatory zoning in a single
crystal of liddicoatite from its type locality, Anjana-
bonoina, central Madagascar, using Electron Micro-
Probe Analysis (EMPA), crystal-Structure REFinement
(SREF), Magic-Angle-Spinning Nuclear Magnetic
Resonance (MAS NMR) spectroscopy and Mössbauer
spectroscopy.
ProVEnAnCE
The pegmatites of central Madagascar were
emplaced about 490 million years ago during late-
stage granitic plutonism related to the Pan-African
event, which occurred from 570 to 455 million years
ago (Paquette & Nédélec 1998). These pegmatites are
hosted by gneisses, marbles and quartzites of the Itremo
Group, which overlies the crystalline basement of the
Mozambique Orogenic Belt (Malisa & Muhongo 1990,
Ashwal & Tucker 1999, Dissanayake & Chandrajith
1999, Collins & Windley 2002, Dirlam et al. 2002).
Although the crystal examined here is known to be
from central Madagascar, we are not certain as to its
exact locality; however, the Anjanabonoina pegmatite,
located about 55 km west–southwest of the city of
Antsirabe in Antannanarivo Province, is famous for
producing such crystals. In support of this provenance,
the tourmaline section examined here (Fig. 1a) bears
a very strong resemblance to the tourmaline from
Anjanabonoina illustrated in Lacroix (1922, Fig. 329).
According to the classication scheme of Černý (1982),
this pegmatite is intermediate between the LCT and
NYF families of the rare-element and miarolitic classes.
The Anjanabonoina pegmatite is enriched in Na and
Li, and has pronounced structural and mineralogical
InTroDUCTIon
Liddicoatite, ideally Ca(Li2Al)Al6(Si6O18)
(BO3)3(OH)3F (Hawthorne & Henry 1999), is a calcic
tourmaline occurring in late-stage mineral assemblages
of rare-element elbaite-subtype pegmatites (see Dirlam
et al. 2002, and references therein). It is a compara-
tively uncommon mineral, as the geological conditions
required for the concentration of both Ca and Li are
unusual; these elements typically show contrasting
geochemical behavior in the later stages of pegmatite
crystallization. Liddicoatite from Madagascar has long
been known for its spectacular patterns of color zoning
(Dunn et al. 1977, 1978). Although liddicoatite occurs at
other localities (e.g., Sahama et al. 1979, Zagorsky et al.
1989, Novák et al. 1999, Teertstra et al. 1999, Dirlam et
al. 2002), crystals from these localities do not show the
elaborate patterns of zoning that have made Malagasy
liddicoatite a highly prized mineral with collectors.
Tourmaline is a useful petrogenetic indicator in
granites and granitic pegmatites (Aurisicchio et al.
1999, Dyar et al. 1999, Novák & Povondra 1995,
Novák et al. 1999, Selway et al. 1999, 2000a, 2000b,
2002, Agrosì et al. 2006, Neiva et al. 2007) and a
wide variety of metamorphic rocks (Henry & Dutrow
1992, 1996, Henry & Guidotti 1985, Povondra &
Novák 1986). There has been considerable work done
on the characterization (e.g., Hawthorne et al. 1993,
MacDonald et al. 1993, Taylor et al. 1995, MacDonald
& Hawthorne 1995, Dyar et al. 1998, Bosi 2008, Bosi
& Lucchesi 2004, Bosi et al. 2004, 2005a, 2005b, Burns
et al. 1994, Bloodaxe et al. 1999, Grice & Ercit 1993,
Grice et al. 1993, Francis et al. 1999, Cámara et al.
2002, Schreyer et al. 2002, Ertl & Hughes 2002, Ertl
et al. 2003a, 2003b, 2004, 2005, 2007, 2008, Hughes
et al. 2000, 2004, Marschall et al. 2004, Andreozzi
et al. 2008, Lussier et al. 2008a, 2008b, 2009) and
zonED LIDDICoATITE From AnJAnABonoInA, mADAGASCAr 65
internal zoning; it contains large miarolitic cavities, up
to ~5 m in dimension, is heavily kaolinized by late-stage
hydrothermal uids, and consists of assemblages of
quartz, feldspar, beryl, hambergite, danburite, phenakite
and scapolite. Pezzotta (1996) reported the geologically
most signicant characteristics of the Anjanabonoina
deposit to be (1) extremely high content of B, resulting
in an abundance of tourmaline and primary danburite,
and (2) the widespread presence of Ca, leading to the
abundance of liddicoatite, danburite and diopside.
BIAxIAL oPTICS In LIDDICoATITE
For over a century, tourmaline showing anoma-
lous biaxiality has been reported (e.g., Braun 1881,
Madelung 1883, Foord & Cunningham 1978, Foord &
Mills 1978, Gorskaya et al. 1982, Akizuki et al. 2001,
Shtukenberg et al. 2007). The origin of the anomalous
optics has been debated for over two centuries (e.g.,
Kahr & McBride 1992). However, it is now generally
believed that the lowering of symmetry results from
(1) ordering of atoms during growth owing to selective
attachment of atoms to sites that are symmetrically
equivalent in the bulk crystal but not at the growing
crystal face (e.g., Akizuki & Sunagawa 1978, Akizuki
& Terada 1998, Akizuki et al. 1979), or (2) intrinsic
stress as a result of compositional inhomogeneity in
the crystal (e.g., Gorskaya et al. 1982). Shtukenberg
et al. (2007) examined in detail a prismatic crystal of
elbaite–liddicoatite from the Malkhan pegmatite eld
FIG. 1. The liddicoatite crystal investigated in this study: (a) slice perpendicular to the
c axis showing oscillatory color zoning; (b) location of samples used for SREF, MAS
NMR, and optical investigation along the strip of crystal extracted from the large crystal
at the location of the red arrow.
66 THE CAnADIAn mInErALoGIST
in the Transbaikal region, Russia, consisting of the
following growth sectors: m{1010}, a{1120}, o{0221}
and r{1011}. They measured the optic axial angle (2V)
and collected single-crystal X-ray intensity data on
three crystals from the o{0221} growth sector with 2V
values of 11(1), 16(1) and 23(1)°, respectively. They
collected a complete Ewald sphere of intensity data on
each of these three crystals and reported a signicant
decrease in R(int) values if reection data were merged
in the monoclinic space-group Cm [R(int) = 1.86–3.15
%] as opposed to the trigonal space group R3m [R(int)
= 5.04–7.24%]. Moreover, ~20–40% of reflections
violate the requirements of the 3 and mi symmetry
operators, but not the my symmetry operator, suggesting
monoclinic symmetry. The R indices for their rene-
ment in R3m, Cm and R1 are 2.20–2.70, 1.86–2.55 and
1.97–2.81%, respectively, and rening the structures
in either monoclinic (Cm) or triclinic (R1) symmetries
gave a direct correlation between the degree of order at
the Y sites and the corresponding 2V angles.
ExPErImEnTAL
The liddicoatite specimen used in this study was
obtained from the Harvard Mineralogical Museum.
It is a slice ~5-mm thick (Fig. 1), cut perpendicular
to the c axis through the pyramidal zoning section of
a much larger crystal, the exact dimensions of which
are unknown. There are four major divisions in color
(from core to edge): (1) purple (~5 cm wide); (2) pale
green (~5 cm wide); (3) dark green (~2 cm wide); (4)
dark green-black (~0.7 cm wide). Each of these major
color divisions consists of many smaller zones (Fig. 1),
which are distinguished by the oscillatory repetition of
diffuse color variations, and bordered by sharp, grayish
green to black boundaries, each of which is inclined at
~45° to the (001) plane. Near the edge of the crystal,
the form of the zones becomes prismatic and sharp as
opposed to diffuse.
Samples were extracted from the main crystal at
four different positions (Fig. 1), and the 2V angles
were measured with a spindle stage and the program
ExCALIBr II (Bartelmehs et al. 1992). Sample L–OPT1,
taken from the purple center of the crystal, has uniaxial
optics (2V = 0.0°); samples L–OPT2 and L–OPT3,
taken from the pyramidal zone, have 2V values of 8(3)
and 18.9(5)°, respectively, and L–OPT4, taken from the
prism zone, has a 2V value of 20.5(9)°.
Collection of X-ray data
Twenty-three small fragments were extracted,
ground to (approximate) spheres and mounted on
a Bruker P3 automated four-circle single-crystal
diffractometer equipped with a serial detector and a
graphite-monochromated MoKa X-radiation source.
Cell dimensions (Table 1) were derived from the setting
angles of thirteen automatically aligned reections by
least-squares renement. A total of ~1110 symmetry-
independent reections was measured for each crystal
over the interval 4° < 2u < 60°, with index ranges 0 <
h < 23, 0 < k < 23, –11 < l < 11. A standard reection
was collected every 50 measurements to monitor instru-
ment stability; no signicant change was noted during
any of the data collections. Psi-scan intensity data were
collected, a psi-scan absorption correction was applied
to each crystal, together with the usual geometrical
corrections, and the data were reduced to structure
factors. Additional details of the data collection and
renement are given in Table 1.
Space group
X-ray intensity data were collected on crystals
denoted here as L–OPT1–4 (with 2V values corre-
sponding to those measured above) using an APEX
CCD detector. In excess of a hemisphere of data was
collected for each crystal in order to test for diffraction
symmetry (Table 2). The calculated R(int) values for
L–OPT1–3 with trigonal symmetry are 1.73, 2.41 and
1.99%, respectively, and with monoclinic symmetry
are 1.38, 1.88 and 1.67%, an insignicant difference.
Shtukenberg et al. (2007) found that cation order at the
three edge-sharing Y octahedra resulted in poor R(int)
values about two of the three mirror planes. We tested
this issue for our three samples: The R(int) values for
groups of reections directly related by each of the
three mirror planes at (x 2x z), (2x x z) and (x –x z) were
calculated. The results (Table 2) indicate no difference
in merge quality for any particular mirror, and all values
of R(int) are <1%. These results provide no evidence of
lower symmetry in the diffraction data, and hence all
structures were rened with R3m symmetry.
Crystal-structure renement
Crystal-structure refinement was done using the
SHELXTL PLUS© (PC version) software package.
All structures were rened with full occupancy of the
Z site by Al and the B site by B in the space group
R3m. All samples were rened twice, once with the
O(1) site at (0,0,z) and the O(2) site at (x,1–x,z), and
again with O(1) at (x,2x,z) and O(2) at (x,y,z) to allow
for positional disorder, as indicated by the high Ueq
values (Burns et al. 1994). The nal renement was
done with neutral scattering factors for all species
except O, for which we used a fully ionized scattering
factor (this procedure will be discussed in detail in
the Results section). Each specimen was tested for
absolute orientation and transformed as appropriate.
An isotropic extinction correction of the form k[1 +
0.001xFc2l3 / sin2u]–1/4 was applied, and the values of
x were in the range 0.0005(2) to 0.0060(3). The highest
positive and negative residual electron-densities in nal
difference-Fourier maps were ~0.5 eÅ–3 at ~0.5 Å from
O(1), associated with minor problems modeling the
zonED LIDDICoATITE From AnJAnABonoInA, mADAGASCAr 67
positional disorder of the anion at O(1), and ~–0.3 eÅ–3
at ~0.25 Å from H(3), associated with delocalization of
electron density along the O(3)–H(3) bond, which was
constrained to be close to 0.98 Å during renement to
give good interatomic distances involving H(3). The
highest correlations in the refinements were of the
order of ~0.84 and involved either the z coordinates of
the T and Z sites or the x and y coordinates of the O(2)
site. Final R1 and wR2 indices are 1.48–2.97% (<R1> =
1.78%) and 3.87–7.37 (<wR2> = 4.71%), respectively
(Table 1) for all observed reections. Atom coordinates
and selected interatomic distances of selected samples
are given in Tables 3 and 4, respectively; rened site-
scattering values (Hawthorne et al. 1995) are given
in Table 5. Structure factors for all structures may be
obtained from the Depository of Unpublished Data on
TABLE 1. D ATA COLLE CTION AND STRUCTURE-REFINEMENT INFORMATION
FOR SAMPLES OF LIDDICOATITE FROM MADAGASCAR
_________________________________________________________________________________________________________
L1 L2 L4 L5 L6 L7 L11 L12
_________________________________________________________________________________________________________
a (Å) 15.8636(16) 15.8529(13) 15.8548(14) 15.8456(12) 15.8418(17) 15.8363(15) 15.8675(13) 15.853(7)
c (Å) 7.1119(9) 7.1101(8) 7.1099(8) 7.1066(7) 7.1044(10) 7.1040(9) 7.1135(8) 7.120(4)
V (Å ) 1551.2(4) 1547.4(3) 1547.9(3) 1545.2(3) 1544.0(4) 1543.0(3) 1551.1(3) 1549.0(1)
3
Color Dark pink Pink Pink Pink Pink Pink Pink Pink
Unique 1111 1111 1111 1111 1111 1111 1111 1111
o
|F | > 4ó1087 1092 1087 1088 1090 1096 1102 1095
1
R (obs.) % 1.77 1.66 1.80 1.70 1.71 1.64 1.73 1.73
2
wR (%) 4.43 4.32 4.45 4.27 4.29 4.11 4.41 4.27
GOOF 1.072 1.072 1.052 1.085 1.083 1.103 1.073 1.065
EXTI* 0.0042(3) 0.0025(2) 0.0028(2) 0.0037(3) 0.0026(2) 0.0037(3) 0.0020(2) 0.0046(3)
1 2
R/wR (%) ** 1.90 / 4.75 1.85 / 4.71 1.94 / 4.66 1.73 / 4.29 1.80 / 4.43 1.75 / 4.30 1.94 / 4.80 1.92 / 4.77
o o
_________________________________________________________________________________________________________
L13 L15 L16 L17 L18 L19 L20 L21
________________________________________________________________________________________________________
a (Å) 15.8449(15) 15.8248(16) 15.8307(10) 15.8337(12) 15.8293(11) 15.8343(11) 15.8303(11) 15.8399(11)
c (Å) 7.1053(9) 7.0993(9) 7.1013(6) 7.1023(7) 7.1003(6) 7.1012(7) 7.1017(6) 7.1030(6)
V (Å ) 1544.9(3) 1539.6(4) 1541.3(2) 1541.9(3) 1540.7(3) 1541.8(3) 1541.2(3) 1543.5(5)
3
Color G reen G reen G reen G reen Green Gree n Gree n Dark green
Unique 1111 1109 1109 1109 1109 1109 1109 1111
o
|F | > 4ó1099 1097 1099 1088 1094 1094 1091 1104
1
R (obs.) % 1.96 2.23 1.44 1.62 1.61 1.69 1.70 1.68
2
wR (%) 4.84 5.89 3.75 4.03 4.09 4.29 4.10 6.03
GOOF 1.099 1.108 1.117 1.071 1.111 1.103 1.104 1.574
EXTI* 0.0026(2) 0.0039(4) 0.0052(3) 0.0034(2) 0.0034(3) 0.0061(3) 0.0034(2) 0.0036(3)
1 2
R/wR (%) ** 2.05 / 5.03 2.32 / 6.11 1.51 / 3.78 1.67 / 4.00 1.72 / 4.31 1.77 / 4.46 1.80 / 4.28 1.87 / 5 05
o o
_________________________________________________________________________________________________________
L22 L23 L24 L25 L26 L27 L28
__________________________________________________________________________________________________________
a (Å) 15.8306(16) 15.8299(13) 15.8286(14) 15.8438(14) 15.8368(11) 15.8333(14) 15.8404(13)
c (Å) 7.0999(9) 7.1009(7) 7.1012(8) 7.1043(8) 7.1014(6) 7.1025(8) 7.1039(7)
V (Å ) 1540.9(4) 1540.9(3) 1540.9(3) 1544.4(3) 1542.4(2) 1541.8(3) 1543.6(3)
3
Color Gre en Green Gre en Dark gree n Da rk green Dark green D ark green
Unique 1109 1109 1109 1111 1109 1109 1111
o
|F | > 4ó1087 1098 1089 1096 1078 1086 1092
1
R (obs.) % 2.95 1.51 1.58 1.83 1.81 1.71 1.54
2
wR (%) 7.16 3.96 4.05 4.88 4.62 4.37 3.93
GOOF 1.070 1.125 1.079 1.096 1.046 1.081 1.092
EXTI* 0.0047(6) 0.0061(3) 0.0400(3) 0.0015(3) 0.0013(2) 0.0007(2) 0.0054(3)
1 2
R/wR (%) ** 2.95 / 7.32 1.64 / 4.27 1.68 / 4.18 1.98 / 5.17 1.88 / 4.60 1.83 / 4.56 1.69 / 4.24
o o
__________________________________________________________________________________________________________
Space group, R3m; Z = 3; Radiation / monochromator: MoK á/graphite. All crystals were ~150–200 ìm ground spheres.
occ
* Ma ximizes agreement between F and Fk [1 + (EXT I) F ë / 1 0 in (2è)] .
23 3 –¼
** W ith O(1) and O(2) constrained to (0, 0, z) and (x, –x, z), respectively.
68 THE CAnADIAn mInErALoGIST
the Mineralogical Association of Canada website [docu-
ment Liddicoatite CM49_63].
Electron-microprobe analysis
All crystals used for the collection of X-ray intensity
data, and crystals from the samples used for MAS NMR
spectroscopy, were analyzed with a Cameca SX–100
electron microprobe operating in wavelength-dispersion
mode with an accelerating voltage of 20 kV, a specimen
current of 15 nA, and a beam diameter of 10 mm. The
following analyzing crystals and standards were used:
TAP: albite (Na); andalusite (Al); diopside (Si); LPET:
orthoclase (K); diopside (Ca); titanite (Ti); PbTe (Pb);
LTAP: fluororiebeckite (F); forsterite (Mg); LLiF:
fayalite (Fe); spessartine (Mn). The data were reduced
and corrected by the PAP method of Pouchou & Pichoir
(1985). Table 6 gives the chemical compositions (mean
of ten determinations) and unit formulae calculated
with the following assumptions, using the Fe3+ / (Fe2+
+ Fe3+) values determined by Mössbauer spectroscopy:
31 anions, OH + F = 4 apfu [in accord with the incident
bond-valence sums at O(1) and O(3)], B = 3 apfu, ZAl
= 6 apfu; all Mn is assumed to be divalent as not all Fe
is trivalent, and Li = (3 – SY) apfu. The normalization
scheme was iterated to self-consistency.
Magic-angle-spinning nuclear magnetic
resonance spectroscopy
A Varian Inova® 600 spectrometer (14.1 T) was
used to record the MAS NMR spectra of 27Al (L =
156.3 MHz) and 11B (L = 194.2 MHz) in four samples;
these are labeled NMR1–NMR4, and their location
on the sample is shown in Figure 1. For each sample,
a weighed amount (~30 mg) of powdered sample
(~15 mm crystallites) was placed in a 3.2 mm (22 mL
capacity) zirconia rotor and spun at spinning speeds of
18–24 ±0.003 kHz in a double-resonance probe. The
optimized recycle delay was determined independently
for each sample; averages were 7 and 5 s for 27Al and
11B, respectively. The nal spectra are composites of
512–3072 averaged scans. Spectra were referenced to
0.1 M H3BO3 as a secondary reference [d = +19.6 ppm
with respect to BF3(CH3CH2)2O], and 0.1 M Al(NO3)3.
Pulse widths were selected to coincide approximately
with a 15° tip angle at an rf nutation frequency of 42
kHz (11B) and 52 kHz (27Al). A spectrum was collected
on each empty rotor prior to sample packing to rule out
cross-contamination and spectral interference from rotor
materials. A Bruker Avance II 900 (21.1 T) spectrometer
was used to record the 27Al (vL = 234.4 MHz) MAS
NMR spectrum of sample NMR2. A 1.3 mm ZrO2 rotor
was spun at 62.000 ± 0.002 kHz, and acquired with a
12° tip angle (vrf = 73 kHz), a recycle delay of 5 s and
1024 co-added transients.
57Fe Mössbauer spectroscopy
The Fe content of this crystal is quite low, averaging
considerably less than 1 wt% FeO, and as a result, we
could not measure Mössbauer spectra for each color
zone. Instead, we measured spectra on aggregate
samples from the pyramidal and prismatic sectors to
give us some basis for treating Fe in the calculation of
the unit formulae. Powdered samples from the pyra-
midal and prismatic zones were mixed with sucrose
and carefully ground under acetone. The mixtures were
loaded into Pb rings (2 mm inner diameter) and covered
by tape on both sides. Mössbauer spectra were acquired
at room temperature in transmission geometry using a
57Co(Rh) point source. The spectrometer was calibrated
with the room-temperature spectrum of a-Fe. The
spectra were t by Lorentzian doublets method using
the RECOIL® software package; tting parameters are
given in Table 7.
rESULTS
MAS NMR spectroscopy
Magic-angle spinning NMR is sensitive to the coor-
dination number of 11B (Bray et al. 1961, Turner et al.
1986) and 27Al (Kirkpatrick 1988, Kirkpatrick et al.
1985, 1986). Chemical shifts of [4]- and [3]-coordinated
B, and [4]- and [6]-coordinated Al, in tourmaline are
well-resolved in MAS NMR spectra (e.g., Tagg et al.
1999, Schreyer et al. 2002, Marler & Ertl 2002, Lussier
et al. 2008a, 2009). For both nuclei, MAS NMR can
be used to detect the presence of very small amounts
of [4]-coordinated species in the presence of much
greater amounts of [3]- and [6]-coordinated B and Al,
respectively. The 11B and 27Al MAS NMR spectra are
presented in Figures 2 and 3, respectively. In all spectra,
only one peak is observed. These spectra clearly lack
any observable intensity in the regions characteristic
for tetrahedrally coordinated species (~0 ppm for B;
50–70 ppm for Al). There is the suggestion of a shoulder
at ~0 ppm in Figure 2b, and the simulated spectra of
TABLE 2. C ALCULA TED R(int) VAL UES* F OR LIDDICOATITE
ACROSS R3m MIRROR PLANES
___________________________________________________________
x, 2x, z 2x, x, z x, –x, z
___________________________________________________________
L-OPT1 R(int) * (%) 2.57 2.54 2.45
N2138 2167 2078
L-OPT2 R(int)4.53 4.43 4.51
N1991 2076 2006
L-OPT3 R(int)3.22 3.08 3.08
N2107 2138 2094
L-OPT4 R(int)4.32 4.39 4.51
N2245 2165 2116
___________________________________________________________
oo o
* averages calculated using Ó|F – <F>| / Ó|F| on N pairs of reflections.
22 2
zonED LIDDICoATITE From AnJAnABonoInA, mADAGASCAr 69
TABLE 3. FINAL POSITIONS* AND EQUIVALENT ISOTROPIC-DISPLACEMENT PARAMETERS (Å ) OF ATOMS
2
IN CRYSTALS OF LIDDICOATITE
_____________________________________________________________________________________________________________
L1 L2 L4 L5 L6 L7 L11 L12
_____________________________________________________________________________________________________________
Xx 0000
0000
y0000
0000
z0.76101(17) 0.76028(14) 0.76060(17) 0.76011(15) 0.76028(15) 0.76057(14) 0.76038(16) 0.76015(15)
eq
U0.0175(3) 0.0157(3) 0.0165(3) 0.0143(3) 0.0145(3) 0.0144(3) 0.0173(3) 0.01604
Yx 0.06192(4) 0.06195(4) 0.06191(4) 0.06192(4) 0.06188(4) 0.06185(4) 0.06200(3) 0.06192(4)
y0.93808(4) 0.93805(4) 0.93809(4) 0.93808(4) 0.93812(4) 0.93815(4) 0.93800(3) 0.93808(4)
z0.36906(15) 0.36814(15) 0.36813(16) 0.36673(17) 0.36596(18) 0.36575(16) 0.37036(14) 0.36940(15)
eq
U0.0113(3) 0.0117(3) 0.0114(3) 0.0117(4) 0.0124(4) 0.0113(3) 0.0108(3) 0.0115(3)
Zx 0.26015(4) 0.25992(3) 0.26002(4) 0.25977(4) 0.25972(4) 0.25973(3) 0.26026(4) 0.26009(4)
y0.29717(4) 0.29700(3) 0.29703(4) 0.29691(3) 0.29686(3) 0.29683(3) 0.29728(3) 0.29709(3)
z0.38793(10) 0.38782(9) 0.38784(10) 0.38791(9) 0.38801(9) 0.38801(9) 0.38757(9) 0.38774(9)
eq
U0.00617(11) 0.00640(10) 0.00647(11) 0.00637(11) 0.00633(11) 0.00640(10) 0.00609(11) 0.00653(10)
Tx 0.19025(3) 0.19020(3) 0.19018(3) 0.19025(3) 0.19023(3) 0.19017(3) 0.19021(3) 0.19020(3)
y0.19213(3) 0.19215(3) 0.19210(3) 0.19215(3) 0.19212(3) 0.19210(3) 0.19214(3) 0.19212(2)
z0000
0000
eq
U0.00496(10) 0.00507(9) 0.00515(10) 0.00511(9) 0.00500(9) 0.00518(9) 0.00493(9) 0.00518(9)
Bx 0.89084(10) 0.89089(9) 0.89101(10) 0.89099(10) 0.89104(10) 0.89115(9) 0.89067(10) 0.89096(9)
y0.10916(10) 0.10911(9) 0.10899(10) 0.10901(10) 0.10896(10) 0.10885(9) 0.10933(10) 0.10904(9)
z0.5448(3) 0.5451(3) 0.5448(4) 0.5446(3) 0.5447(3) 0.5444(3) 0.5451(3) 0.5454(3)
eq
U0.0064(4) 0.0068(4) 0.0072(4) 0.0075(4) 0.0068(4) 0.0069(4) 0.0069(4) 0.0069(4)
O(1) x0.01155(15) 0.01152(13) 0.01134(15) 0.01136(15) 0.01128(15) 0.01111(14) 0.01214(13) 0.01165(13)
d
y0.0231(3) 0.0230(3) 0.0227(3) 0.0227(3) 0.0226(3) 0.0222(3) 0.0243(3) 0.0233(3)
z0.2115(5) 0.2118(5) 0.2125(5) 0.2119(5) 0.2114(5) 0.2117(5) 0.2112(5) 0.2111(5)
eq
U0.0149(11) 0.014(1) 0.0144(11) 0.0151(11) 0.0145(11) 0.014(1) 0.014(1) 0.012(1)
O(1) x0000
0000
o
y0000
0000
z0.2117(6) 0.2120(5) 0.2126(5) 0.2121(5) 0.2115(5) 0.2118(5) 0.2114(6) 0.2113(6)
eq
U0.0566(14) 0.0554(13) 0.0537(13) 0.0551(13) 0.0540(13) 0.0522(12) 0.0612(16) 0.0549(14)
O(2) x0.9302(2) 0.9304(2) 0.9308(2) 0.9305(2) 0.9306(2) 0.9309(2) 0.9298(2) 0.9300(2)
d
y0.0508(2) 0.0505(2) 0.0511(2) 0.0509(2) 0.0509(2) 0.0510(2) 0.0507(2) 0.0505(2)
z0.5200(3) 0.5197(3) 0.5195(3) 0.5196(3) 0.5196(3) 0.5197(2) 0.5207(3) 0.5202(3)
eq
U0.0087(5) 0.0102(5) 0.0088(5) 0.0088(5) 0.0092(5) 0.0095(4) 0.0090(5) 0.0088(4)
O(2) x0.93974(7) 0.93998(7) 0.93983(7) 0.93986(7) 0.93990(7) 0.94001(7) 0.93960(7) 0.93979(7)
o
y0.06026(7) 0.06002(7) 0.06017(7) 0.06014(7) 0.06010(7) 0.05999(7) 0.06040(7) 0.06021(7)
z0.5202(4) 0.5199(3) 0.5197(3) 0.5198(3) 0.5198(3) 0.5199(3) 0.5209(3) 0.5203(3)
eq
U0.0171(5) 0.0183(5) 0.0162(5) 0.0167(4) 0.0171(4) 0.0169(4) 0.0180(5) 0.0176(5)
O(3) x0.13483(7) 0.13490(7) 0.13478(7) 0.13478(7) 0.13493(7) 0.13484(7) 0.13504(7) 0.13492(7)
y0.86517(7) 0.86510(7) 0.86522(7) 0.86522(7) 0.86507(7) 0.86516(7) 0.86496(7) 0.86508(7)
z0.4897(2) 0.4893(2) 0.4895(2) 0.4895(2) 0.4899(2) 0.4896(2) 0.4894(2) 0.4894(2)
eq
U0.0100(3) 0.0102(3) 0.0101(4) 0.0104(3) 0.0103(3) 0.0104(3) 0.0091(3) 0.0102(3)
O(4) x0.90771(7) 0.90773(6) 0.90773(7) 0.90781(7) 0.90780(6) 0.90786(6) 0.90755(6) 0.90767(6)
y0.09229(7) 0.09227(6) 0.09227(7) 0.09219(7) 0.09220(6) 0.09214(6) 0.09245(6) 0.09233(6)
z0.9269(2) 0.9263(2) 0.9265(2) 0.9255(2) 0.9256(2) 0.9257(2) 0.9268(2) 0.9268(2)
eq
U0.0080(3) 0.0081(3) 0.0082(3) 0.0087(3) 0.0084(3) 0.0085(3) 0.0078(3) 0.0085(3)
O(5) x0.09234(7) 0.09213(6) 0.09226(7) 0.09217(7) 0.09210(7) 0.09203(6) 0.09244(7) 0.09227(6)
y0.90766(7) 0.90787(6) 0.90774(7) 0.90783(7) 0.90790(7) 0.90797(6) 0.90756(7) 0.90773(6)
z0.9054(2) 0.9047(2) 0.9048(2) 0.9041(2) 0.9042(2) 0.9042(2) 0.9053(2) 0.9051(2)
eq
U0.0082(3) 0.0086(3) 0.0090(3) 0.0082(3) 0.0085(3) 0.0084(3) 0.0081(3) 0.0088(3)
O(6) x0.18672(8) 0.18644(8) 0.18634(8) 0.18640(8) 0.18632(8) 0.18607(8) 0.18694(8) 0.18674(8)
y0.19640(8) 0.19624(8) 0.19616(8) 0.19590(8) 0.19597(8) 0.19593(8) 0.19657(8) 0.19646(8)
z0.22361(17) 0.22358(16) 0.22358(18) 0.22349(17) 0.22365(17) 0.22357(16) 0.22355(17) 0.22354(16)
eq
.U0.0074(2) 0.0074(2) 0.0074(2) 0.0071(2) 0.0071(2) 0.0071(2) 0.0073(2) 0.0073(2)
O(7) x0.28551(8) 0.28547(7) 0.28554(8) 0.28537(8) 0.28534(8) 0.28541(7) 0.28546(8) 0.28551(7)
y0.28578(8) 0.28581(8) 0.28588(8) 0.28589(8) 0.28596(8) 0.28596(8) 0.28565(8) 0.28579(8)
z0.91842(16) 0.91820(15) 0.91854(16) 0.91828(16) 0.91837(16) 0.91831(15) 0.91811(16) 0.91824(15)
eq
U0.0063(2) 0.0063(2) 0.0064(2) 0.0064(2) 0.0064(2) 0.0065(2) 0.0062(2) 0.0064(2)
O(8) x0.27012(9) 0.27016(8) 0.27019(9) 0.27004(9) 0.27000(9) 0.26996(8) 0.27017(9) 0.27016(9)
y0.20968(9) 0.20953(8) 0.20964(9) 0.20972(9) 0.20969(9) 0.20947(8) 0.20974(8) 0.20967(8)
z0.55784(17) 0.55771(16) 0.55767(17) 0.55772(16) 0.55794(17) 0.55779(15) 0.55749(17) 0.55772(16)
eq
U0.0075(2) 0.0077(2) 0.0076(2) 0.0075(2) 0.0076(2) 0.0074(2) 0.0076(2) 0.0082(2)
H(3) x0.1337(12) 0.130(2) 0.1303(12) 0.1321(12) 0.1306(12) 0.1279(12) 0.1319(12) 0.1311(12)
y0.8663(12) 0.870(2) 0.8697(12) 0.8679(12) 0.8694(12) 0.8721(12) 0.8681(12) 0.8689(12)
z0.624(3) 0.6256(13) 0.625(3) 0.623(3) 0.622(3) 0.620(3) 0.623(3) 0.624(3)
eq
U** 0.015 0.015 0.015 0.015 0.015 0.015 0.015 0.015
_____________________________________________________________________________________________________________
* The superscripts o and d on O(1) and O (2) denote the ordered and disordered atom coordinates for these sites.
** Fixed d uring the refinement.
70 THE CAnADIAn mInErALoGIST
TABLE 3 (c on t’d). FINAL POSITIONS* AND EQUIVALENT ISOTROPIC-DISPLACEMENT PARAMETERS (Å ) OF ATOMS
2
IN CRYSTALS OF LIDDICOATITE
_____________________________________________________________________________________________________________
L13 L15 L16 L17 L18 L19 L20 L21
_____________________________________________________________________________________________________________
Xx0000
0000
y0000
0000
z0.76231(19) 0.76133(17) 0.76121(12) 0.76167(14) 0.76118(14) 0.76142(14) 0.76161(15) 0.76207(15)
eq
U0.0161(4) 0.0134(3) 0.0142(2) 0.0148(3) 0.0140(3) 0.0141(3) 0.0136(3) 0.0147(3)
Yx 0.06196(5) 0.06182(6) 0.06184(4) 0.06183(4) 0.06182(4) 0.06186(4) 0.06175(5) 0.06183(4)
y0.93804(5) 0.93818(6) 0.93816(4) 0.93817(4) 0.93818(4) 0.93814(4) 0.93825(5) 0.93817(4)
z0.36590(19) 0.3637(2) 0.36437(16) 0.36458(17) 0.36366(18) 0.36396(18) 0.36394(19) 0.36477(17)
eq
U0.0110(4) 0.0113(5) 0.0103(3) 0.0110(3) 0.0110(4) 0.0110(4) 0.0103(4) 0.0105(4)
Zx 0.25978(4) 0.25956(4) 0.25959(3) 0.25965(3) 0.25957(3) 0.25958(3) 0.25959(4) 0.25969(3)
y0.29699(4) 0.29670(4) 0.29671(3) 0.29678(3) 0.29670(3) 0.29672(3) 0.29668(3) 0.29684(3)
z0.38818(11) 0.38834(11) 0.38825(8) 0.38821(9) 0.38821(9) 0.38819(9) 0.38827(9) 0.38829(9)
eq
U0.00631(12) 0.00608(13) 0.00608(9) 0.00616(10) 0.00626(10) 0.00609(10) 0.00590(10) 0.00592(10)
Tx 0.19019(4) 0.19020(3) 0.19018(3) 0.19020(3) 0.19018(3) 0.19019(3) 0.19017(3) 0.19020(3)
y0.19212(3) 0.19210(3) 0.19206(2) 0.19211(3) 0.19211(3) 0.19210(3) 0.19207(3) 0.19212(3)
z0000
0000
eq
U0.00539(11) 0.00509(12) 0.00493(8) 0.00530(9) 0.00528(9) 0.00509(9) 0.00471(9) 0.00494(9)
Bx 0.89082(11) 0.89111(11) 0.89126(8) 0.89120(9) 0.89123(9) 0.89106(9) 0.89135(10) 0.89109(10)
y0.10918(11) 0.10889(11) 0.10874(8) 0.10880(9) 0.10877(9) 0.10894(9) 0.10865(10) 0.10891(10)
z0.5450(4) 0.5446(4) 0.5447(3) 0.5444(3) 0.5444(3) 0.5447(3) 0.5448(3) 0.5449(3)
eq
U0.0073(5) 0.0067(5) 0.0068(3) 0.0071(4) 0.0069(4) 0.0069(4) 0.0070(4) 0.0068(4)
O(1) x0.01115(17) 0.01091(17) 0.01085(12) 0.01108(14) 0.01073(14) 0.01096(14) 0.01078(15) 0.01101(15)
d
y0.0223(4) 0.0218(3) 0.0217(2) 0.0222(3) 0.0215(3) 0.0219(3) 0.0216(3) 0.0220(3)
z0.2128(6) 0.2114(6) 0.2115(4) 0.2120(5) 0.2108(4) 0.2114(5) 0.2114(5) 0.2119(5)
eq
U0.0158(12) 0.0148(12) 0.0131(9) 0.015(1) 0.013(1) 0.014(1) 0.0138(11) 0.0152(11)
O(1) x0000
0000
o
y0000
0000
z0.2130(6) 0.2116(7) 0.2117(5) 0.2121(5) 0.2110(5) 0.2115(5) 0.2117(5) 0.2123(7)
eq
U0.0546(15) 0.0522(15) 0.0492(10) 0.0521(12) 0.0482(11) 0.0518(12) 0.0491(12) 0.0535(15)
O(2) x0.9306(3) 0.93061(2) 0.93127(19) 0.9311(2) 0.9313(2) 0.9311(2) 0.9314(2) 0.9307(2)
d
y0.0511(3) 0.0506(2) 0.05097(19) 0.0511(2) 0.0511(2) 0.0510(2) 0.0510(2) 0.0509(2)
z0.5190(3) 0.5188(3) 0.5194(2) 0.5187(2) 0.5191(2) 0.5190(2) 0.5191(3) 0.5190(3)
eq
U0.0090(5) 0.0082(5) 0.0093(4) 0.0091(4) 0.0092(4) 0.0089(4) 0.0086(5) 0.0089(5)
O(2) x0.93980(8) 0.94007(8) 0.94020(6) 0.94006(7) 0.94015(7) 0.94010(7) 0.94025(7) 0.94008(8)
o
y0.06020(8) 0.05993(8) 0.05980(6) 0.05994(7) 0.05985(7) 0.05990(7) 0.05975(7) 0.05992(8)
z0.5191(4) 0.5188(4) 0.5197(3) 0.5189(3) 0.5193(3) 0.5190(3) 0.5193(3) 0.5195(3)
eq
U0.0167(5) 0.0164(5) 0.0164(4) 0.0162(4) 0.0161(4) 0.0162(4) 0.0157(4) 0.0168(5)
O(3) x0.13458(8) 0.13465(8) 0.13462(6) 0.13461(7) 0.13448(7) 0.13455(7) 0.13470(7) 0.13454(7)
y0.86542(8) 0.86535(8) 0.86538(6) 0.86539(7) 0.86552(7) 0.86545(7) 0.86530(7) 0.86546(7)
z0.4900(3) 0.4902(3) 0.48995(19) 0.4899(2) 0.4899(2) 0.4899(2) 0.4902(2) 0.4900(2)
eq
U0.0100(4) 0.0105(4) 0.0107(3) 0.0106(3) 0.0111(3) 0.0105(3) 0.0104(3) 0.0102(3)
O(4) x0.90765(7) 0.90785(8) 0.90791(5) 0.90785(6) 0.90791(6) 0.90793(6) 0.90792(6) 0.90782(6)
y0.09235(7) 0.09215(8) 0.09209(5) 0.09215(6) 0.09209(6) 0.09207(6) 0.09208(6) 0.09218(6)
z0.9255(3) 0.9248(3) 0.92522(19) 0.9253(2) 0.9252(2) 0.9248(2) 0.9252(2) 0.9257(2)
eq
U0.0085(4) 0.0084(4) 0.0084(3) 0.0084(3) 0.0083(3) 0.0081(3) 0.0077(3) 0.0080(3)
O(5) x0.09219(8) 0.09192(8) 0.09198(6) 0.09199(6) 0.09197(6) 0.09207(6) 0.09194(7) 0.09204(7)
y0.90781(8) 0.90808(8) 0.90802(6) 0.90801(6) 0.90803(6) 0.90793(6) 0.90806(7) 0.90796(7)
z0.9043(3) 0.9042(3) 0.90386(19) 0.9039(2) 0.9037(2) 0.9040(2) 0.9037(2) 0.9041(2)
eq
U0.0085(3) 0.0079(3) 0.0083(3) 0.0088(3) 0.0085(3) 0.0083(3) 0.0078(3) 0.0086(3)
O(6) x0.18640(10) 0.18579(10) 0.18587(7) 0.18605(8) 0.18598(8) 0.18595(8) 0.18585(8) 0.18617(8)
y0.19593(9) 0.19537(9) 0.19569(7) 0.19576(8) 0.19565(7) 0.19554(8) 0.19565(8) 0.19579(8)
z0.22381(19) 0.2233(2) 0.22358(14) 0.22368(16) 0.22373(16) 0.22357(16) 0.22351(17) 0.22380(17)
eq
U0.0073(2) 0.0072(3) 0.00718(18) 0.0072(2) 0.0075(2) 0.0070(2) 0.0068(2) 0.0071(2)
O(7) x0.28531(9) 0.28522(9) 0.28539(6) 0.28538(7) 0.28547(7) 0.28524(7) 0.28545(8) 0.28527(8)
y0.28582(9) 0.28582(9) 0.28599(7) 0.28594(7) 0.28610(7) 0.28589(7) 0.28601(8) 0.28596(8)
z0.91855(18) 0.91856(18) 0.91839(13) 0.91839(14) 0.91847(14) 0.91828(15) 0.91848(15) 0.91863(15)
eq
U0.0063(2) 0.0063(2) 0.00602(17) 0.00614(19) 0.00617(19) 0.00618(19) 0.0059(2) 0.0061(2)
O(8) x0.27008(10) 0.26990(10) 0.26990(7) 0.26986(8) 0.26992(8) 0.26999(8) 0.26981(9) 0.27006(9)
y0.20974(10) 0.20955(10) 0.20948(7) 0.20952(8) 0.20950(8) 0.20964(8) 0.20944(8) 0.20969(9)
z0.55830(19) 0.55810(19) 0.55815(14) 0.55796(15) 0.55805(15) 0.55817(15) 0.55806(16) 0.55831(16)
eq
U0.0076(3) 0.0076(3) 0.00735(19) 0.0074(2) 0.0074(2) 0.0072(2) 0.0069(2) 0.0074(2)
H(3) x0.13312(14) 0.1384(14) 0.1325(11) 0.1320(11) 0.1294(11) 0.1316(12) 0.1293(12) 0.1350(12)
y0.8668(14) 0.8616(14) 0.8675(11) 0.8680(11) 0.8706(11) 0.8684(12) 0.8708(12) 0.8650(12)
z0.625(3) 0.625(3) 0.624(2) 0.622(2) 0.624(3) 0.623(3) 0.624(3) 0.626(3)
eq
U** 0.015 0.015 0.015 0.015 0.015 0.015 0.015 0.015
_____________________________________________________________________________________________________________
* The superscripts o and d on O(1) and O (2) denote the ordered and disordered atom coordinates for these sites.
** Fixed d uring the refinement.
zonED LIDDICoATITE From AnJAnABonoInA, mADAGASCAr 71
TABLE 3 (c on t’d). FINAL POSITIONS* AND EQUIVALENT ISOTROPIC-DISPLACEMENT PARAMETERS (Å ) OF ATOMS
2
IN CRYSTALS OF LIDDICOATITE
_____________________________________________________________________________________________________________
L22 L23 L24 L25 L26 L27 L28
_____________________________________________________________________________________________________________
Xx0000
000
y0000
000
z0.7613(2) 0.76143(13) 0.76087(14) 0.76157(16) 0.76167(16) 0.76151(15) 0.76133(14)
eq
U0.0135(4) 0.0141(3) 0.0137(3) 0.0144(3) 0.0146(3) 0.0147(3) 0.0153(3)
Yx 0.06180(7) 0.06195(4) 0.06187(5) 0.06196(5) 0.06181(5) 0.06183(5) 0.06210(4)
y0.93820(7) 0.93805(4) 0.93813(5) 0.93804(5) 0.93819(5) 0.93817(5) 0.93790(4)
z0.3644(3) 0.36442(16) 0.36431(18) 0.36551(18) 0.36473(19) 0.36530(18) 0.36663(16)
eq
U0.0093(6) 0.0104(4) 0.0110(4) 0.0098(4) 0.0117(4) 0.0112(4) 0.0104(3)
Zx 0.25963(5) 0.25958(3) 0.25962(3) 0.25973(4) 0.25973(4) 0.25964(4) 0.25975(3)
y0.29673(5) 0.29670(3) 0.29673(3) 0.29684(4) 0.29686(4) 0.29677(3) 0.29691(3)
z0.38811(13) 0.38819(8) 0.38823(9) 0.38806(10) 0.38801(10) 0.38811(9) 0.38799(8)
eq
U0.00570(16) 0.00602(9) 0.00610(10) 0.00601(11) 0.00606(11) 0.00613(10) 0.00619(10)
Tx 0.19025(4) 0.19019(3) 0.19019(3) 0.19018(3) 0.19014(3) 0.19022(3) 0.19019(3)
y0.19212(4) 0.19212(2) 0.19209(3) 0.19211(3) 0.19207(3) 0.19214(3) 0.19212(3)
z0000
000
eq
U0.00454(15) 0.00503(8) 0.00501(9) 0.00480(10) 0.00490(10) 0.00500(9) 0.00504(9)
Bx 0.89128(13) 0.89117(8) 0.89119(9) 0.89103(10) 0.89129(10) 0.89123(10) 0.89101(9)
y0.10872(13) 0.10883(8) 0.10881(9) 0.10897(10) 0.10871(10) 0.10877(10) 0.10899(9)
z0.5457(5) 0.5447(3) 0.5453(3) 0.5447(3) 0.5444(4) 0.5450(3) 0.5448(3)
eq
U0.0066(6) 0.0068(4) 0.0066(4) 0.0065(4) 0.0061(4) 0.0067(4) 0.0067(4)
O(1) x0.0109(2) 0.01083(13) 0.01087(14) 0.01128(14) 0.01074(15) 0.01099(14) 0.01123(13)
d
y0.0217(4) 0.0217(3) 0.0217(3) 0.0226(3) 0.0215(3) 0.0220(3) 0.0225(3)
z0.2119(7) 0.2114(4) 0.2116(5) 0.2119(5) 0.2117(5) 0.2119(5) 0.2120(5)
eq
U0.0129(14) 0.0140(9) 0.0136(10) 0.0125(10) 0.0037(11) 0.0131(10) 0.0144(9)
O(1) x0000
000
o
y0000
000
z0.2121(7) 0.2116(5) 0.2118(5) 0.2121(6) 0.2120(5) 0.2118(5) 0.2122(5)
eq
U0.0494(17) 0.0500(11) 0.0498(11) 0.0526(14) 0.0533(13) 0.0501(12) 0.0534(12)
O(2) x0.9317(3) 0.93117(19) 0.9310(2) 0.9308(2) 0.9312(2) 0.9307(2) 0.9309(2)
d
y0.0515(4) 0.05087(19) 0.0510(2) 0.0509(2) 0.0513(3) 0.0507(2) 0.0510(2)
z0.5196(4) 0.5195(2) 0.5192(2) 0.5194(3) 0.5192(3) 0.5198(3) 0.5198(2)
eq
U0.0103(7) 0.0088(4) 0.00864 0.0079(5) 0.0092(5) 0.0080(5) 0.0086(4)
O(2) x0.94016(9) 0.94020(6) 0.94008(6) 0.94003(8) 0.94003(7) 0.94003(7) 0.94000(7)
o
y0.05984(9) 0.05980(6) 0.05992(6) 0.05997(8) 0.05997(7) 0.05997(7) 0.06000(7)
z0.5198(4) 0.5197(3) 0.5195(3) 0.5196(3) 0.5199(3) 0.5198(3) 0.5199(3)
eq
U0.0167(6) 0.0162(4) 0.0160(4) 0.0157(5) 0.0160(4) 0.0159(4) 0.0160(4)
O(3) x0.13446(10) 0.13461(6) 0.13465(7) 0.13475(7) 0.13473(7) 0.13484(7) 0.13473(6)
y0.86554(10) 0.86539(6) 0.86535(7) 0.86525(7) 0.86527(7) 0.86516(7) 0.86527(6)
z0.4897(3) 0.4898(2) 0.4900(2) 0.4900(2) 0.4903(3) 0.4899(2) 0.4897(2)
eq
U0.0100(5) 0.0104(3) 0.0103(3) 0.0098(3) 0.0098(4) 0.0103(3) 0.0102(3)
O(4) x0.90789(9) 0.90778(6) 0.90786(6) 0.90785(7) 0.90784(7) 0.90794(6) 0.90788(6)
y0.09211(9) 0.09222(6) 0.09214(6) 0.09215(7) 0.09216(7) 0.09206(6) 0.09212(6)
z0.9251(3) 0.9251(2) 0.9252(2) 0.9255(2) 0.9254(2) 0.9255(2) 0.9257(2)
eq
U0.0075(4) 0.0082(3) 0.0081(3) 0.0080(3) 0.0081(3) 0.0083(3) 0.0084(3)
O(5) x0.09201(9) 0.09197(6) 0.09191(6) 0.09202(7) 0.09199(7) 0.09200(7) 0.09206(6)
y0.90799(9) 0.90803(6) 0.90809(6) 0.90798(7) 0.90801(7) 0.90800(7) 0.90794(6)
z0.9037(3) 0.90347(19) 0.9036(2) 0.9040(2) 0.9040(2) 0.9041(2) 0.9044(2)
eq
U0.0084(4) 0.0083(3) 0.0084(3) 0.0079(3) 0.0085(3) 0.0087(3) 0.0082(3)
O(6) x0.18584(12) 0.18598(7) 0.18601(8) 0.18627(9) 0.18617(9) 0.18609(8) 0.18633(7)
y0.19559(11) 0.19565(7) 0.19570(8) 0.19593(9) 0.19589(9) 0.19576(8) 0.19591(7)
z0.2238(3) 0.22363(15) 0.22385(16) 0.22362(18) 0.22343(18) 0.22360(17) 0.22364(15)
eq
U0.0066(3) 0.00692(19) 0.0074(2) 0.0068(2) 0.0071(2) 0.0068(2) 0.0071(2)
O(7) x0.28535(11) 0.28533(7) 0.28541(7) 0.28533(8) 0.28545(8) 0.28528(8) 0.28542(7)
y0.28610(11) 0.28597(7) 0.28595(8) 0.28590(8) 0.28601(8) 0.28590(8) 0.28587(7)
z0.9183(2) 0.91836(14) 0.91837(15) 0.91835(17) 0.91837(17) 0.91825(16) 0.91841(14)
eq
U0.0061(3) 0.00607(18) 0.0062(2) 0.0062(2) 0.0061(2) 0.0063(2) 0.00608(19)
O(8) x0.26992(12) 0.26995(7) 0.26994(8) 0.27008(9) 0.26993(9) 0.26999(9) 0.26994(8)
y0.20946(12) 0.20957(7) 0.20947(8) 0.20966(9) 0.20961(9) 0.20960(8) 0.20957(8)
z0.5582(2) 0.55790(14) 0.55795(16) 0.55791(18) 0.55783(17) 0.55798(16) 0.55782(15)
eq
U0.0072(3) 0.00736(19) 0.0074(2) 0.0075(2) 0.0073(2) 0.0073(2) 0.0076(2)
H(3) x0.1307(18) 0.1308(11) 0.1328(12) 0.1316(14) 0.1272(13) 0.1312(12) 0.1339(11)
y0.8693(18) 0.8692(11) 0.8672(12) 0.8684(14) 0.8728(13) 0.8688(12) 0.8661(11)
z0.625(3) 0.622(2) 0.623(2) 0.623(3) 0.618(3) 0.622(3) 0.625(2)
eq
U** 0.015 0.015 0.015 0.015 0.015 0.015 0.015
____________________________________________________________________________________________________________
* The superscripts o and d on O(1) and O (2) denote the ordered and disordered atom coordinates for these sites.
** Fixed d uring the refinement.
72 THE CAnADIAn mInErALoGIST
Figure 3 suggest a [4]B content of ~0.01–0.02 apfu.
The remaining spectra indicate that neither [4]Al nor [4]
B is present in quantities detectable by MAS NMR in
this crystal.
Ultrahigh-eld NMR (21.1 T) and ultrafast MAS
(62 kHz) were used in conjunction on one sample to
reduce the second-order quadrupolar broadening and
minimize any paramagnetic interactions. The [6]Al peak
narrowed by a factor of 2 in ppm relative to the 14.1
T data, thereby increasing the spectral resolution and
verifying that no [4]Al signal is evident (data not shown).
A requirement for MAS NMR spectroscopy is that
the sample under investigation be low in paramagnetic
constituents (e.g., Fe2+, Mn2+). In a detailed study of 11B
and 27Al MAS NMR spectra collected on 50 different
samples of tourmaline, Lussier et al. (2009) showed that
in samples with extremely low contents of paramagnetic
ions (Fe2+ + Mn2+ < 0.05 apfu), [4]B and [4]Al signals
are easily resolved by MAS NMR, but the presence of
greater than ~0.1 apfu transition metals may degrade
the spectrum considerably through signal broadening,
thereby increasing the limit of detection of tetrahedrally
coordinated species.
Limits of detectibility of [4]B and [4]Al
in liddicoatite by MAS NMR
We decided to investigate the limit of detectability
of [4]-coordinated B and Al in tourmaline by 11B and
27Al MAS NMR by simulation. We took the experi-
mental spectra shown in Figures 2a,d and 3a,d (in order
to accommodate the peak broadening expected for
samples containing different amounts of paramagnetic
constituents) and added component peaks at 0 and
70 ppm corresponding to [4]-coordinated B and Al
in tourmaline (Lussier et al. 2008a, 2009), with rela-
tive intensities corresponding to a range of amounts
of [4]-coordinated B and Al from 0.15 to 0.005 apfu.
The widths of the inserted peaks were calculated in
the following manner. The ratios of the widths of the
[3]B and [4]B peaks and the [4]Al and [6]Al peaks in the
spectra of Lussier et al. (2009) were used to calculate
the widths of the [4]B and [4]Al peaks in the simulated
spectra. The results are shown in Figure 4; peaks corre-
sponding to [4]-coordinated B and Al are discernable
down to [4]B and [4]Al contents of 0.02 and 0.01 apfu
for low contents of paramagnetic ions (<0.04 apfu) and
TABLE 4. INTERATOMIC DIS TANCES (Å) IN LIDDICOATITE
________________________________________________________________________________
L1 L2 L4 L5 L6 L7 L11 L12
________________________________________________________________________________
X–O(2) ×3 2.389(2) 2.381(2) 2.386(2) 2.381(2) 2.381(2) 2.379(2) 2.386(2) 2.384(2)
X–O(4) ×3 2.797(2) 2.795(2) 2.795(2) 2.790(2) 2.789(2) 2.786(2) 2.803(2) 2.799(2)
X–O(5) ×3 2.737(2) 2.730(2) 2.733(2) 2.729(2) 2.726(2) 2.723(2) 2.742(2) 2.736(2)
<X–O>2.641 2.635 2.638 2.633 2.632 2.629 2.644 2.640
Y–O(1) 1.781(4) 1.776(4) 1.776(4) 1.771(4) 1.770(4) 1.771(4) 1.778(4) 1.782(4)
d
Y–O(1) ×2 2.189(3) 2.183(3) 2.178(3) 2.174(3) 2.170(3) 2.165(3) 2.206(3) 2.192(3)
d
Y–O(2) ×2 1.885(3) 1.884(3) 1.889(3) 1.892(3) 1.893(3) 1.895(3) 1.882(3) 1.881(3)
d
Y–O(2) ×2 2.107(3) 2.107(3) 2.101(3) 2.109(3) 2.109(3) 2.106(3) 2.111(3) 2.108(3)
d
Y–O(3) 2.179(2) 2.180(2) 2.179(2) 2.182(2) 2.189(2) 2.187(2) 2.179(2) 2.179(2)
Y–O(6) ×2 2.009(1) 2.001(1) 2.000(2) 1.995(2) 1.990(2) 1.987(1) 2.016(1) 2.010(2)
Y–O(1) 2.037(3) 2.031(2) 2.029(3) 2.024(3) 2.022(2) 2.019(2) 2.045(4) 2.039(3)
o
Y–O(2) ×2 1.994(2) 1.993(2) 1.993(2) 1.998(2) 2.000(2) 1.999(2) 1.994(2) 1.992(2)
o
Y–O(3) 2.178(2) 2.180(2) 2.178(3) 2.182(2) 2.189(2) 2.186(2) 2.178(2) 2.178(3)
Y–O(6) ×2 2.008(2) 2.001(2) 2.000(2) 1.994(2) 1.990(2) 1.987(2) 2.016(2) 2.010(2)
<Y–O > 2.037 2.033 2.032 2.032 2.032 2.030 2.041 2.037
o
Z–O(3) 1.949(1) 1.944(1) 1.947(1) 1.943(1) 1.942(1) 1.941(1) 1.950(1) 1.947(1)
Z–O(6) 1.848(1) 1.847(1) 1.849(1) 1.849(1) 1.847(1) 1.848(1) 1.846(1) 1.846(1)
Z–O(7) 1.883(1) 1.884(1) 1.885(1) 1.886(1) 1.887(1) 1.885(1) 1.883(1) 1.885(1)
Z–O(7) 1.960(1) 1.961(1) 1.958(1) 1.961(1) 1.961(1) 1.960(1) 1.960(1) 1.960(1)
Z–O(8) 1.886(1) 1.887(1) 1.887(1) 1.887(1) 1.887(1) 1.888(1) 1.885(1) 1.886(1)
Z–O(8) 1.906(1) 1.906(1) 1.905(1) 1.902(1) 1.902(1) 1.903(1) 1.906(1) 1.906(1)
<Z–O>1.905 1.905 1.905 1.905 1.904 1.904 1.905 1.905
T–O(4) 1.626(1) 1.627(1) 1.626(1) 1.628(1) 1.627(1) 1.626(1) 1.627(1) 1.626(1)
T–O(5) 1.642(1) 1.642(1) 1.642(1) 1.644(1) 1.643(1) 1.642(1) 1.642(1) 1.642(1)
T–O(6) 1.594(1) 1.593(1) 1.593(1) 1.592(1) 1.592(1) 1.592(1) 1.594(1) 1.595(2)
T–O(7) 1.607(1) 1.607(1) 1.608(1) 1.605(1) 1.605(1) 1.606(1) 1.607(1) 1.607(1)
<T–O>1.617 1.617 1.617 1.617 1.617 1.617 1.618 1.618
B–O(2) 1.362(3) 1.367(3) 1.359(3) 1.360(3) 1.360(3) 1.358(3) 1.363(3) 1.360(3)
B–O(8) ×2 1.384(2) 1.382(2) 1.385(2) 1.386(2) 1.385(2) 1.384(2) 1.383(2) 1.385(2)
<B–O>1.377 1.377 1.376 1.377 1.377 1.375 1.376 1.377
____________________________________________________________________________
______
zonED LIDDICoATITE From AnJAnABonoInA, mADAGASCAr 73
TABLE 4 (co nt’d ). INTERATOMIC D ISTANCES (Å ) IN LIDDICOATITE
______________________________________________________________________________
_____
L13 L15 L16 L17 L18 L19 L20 L21
_________________________________________________________________________________
__
X–O(2) ×3 2.397(2) 2.386(2) 2.379(2) 2.388(2) 2.382(2) 2.385(2) 2.382(2) 2.391(2)
X–O(4) ×3 2.787(2) 2.780(2) 2.781(2) 2.782(2) 2.780(2) 2.779(2) 2.779(2) 2.783(2)
X–O(5) ×3 2.724(2) 2.716(2) 2.718(2) 2.718(2) 2.717(2) 2.720(2) 2.715(2) 2.719(2)
<X–O>2.636 2.627 2.626 2.629 2.626 2.628 2.625 2.631
Y–O(1) 1.768(5) 1.765(5) 1.770(3) 1.764(4) 1.772(4) 1.767(4) 1.768(4) 1.767(4)
d
Y–O(1) ×2 2.165(4) 2.153(4) 2.156(3) 2.158(3) 2.153(3) 2.157(3) 2.151(3) 2.159(3)
d
Y–O(2) ×2 1.895(3) 1.894(3) 1.899(3) 1.897(3) 1.901(3) 1.900(3) 1.898(3) 1.895(3)
d
Y–O(2) ×2 2.108(3) 2.112(3) 2.105(2) 2.103(3) 2.105(3) 2.107(3) 2.103(3) 2.109(3)
d
Y–O(3) 2.179(3) 2.189(3) 2.186(2) 2.185(2) 2.185(2) 2.185(2) 2.192(2) 2.184(2)
Y–O(6) ×2 1.990(2) 1.976(2) 1.979(1) 1.982(1) 1.977(1) 1.978(1) 1.979(2) 1.984(1)
Y–O(1) 2.018(3) 2.010(3) 2.013(2) 2.012(2) 2.012(2) 2.013(2) 2.009(2) 2.013(3)
o
Y–O(2) ×2 1.999(2) 2.000(2) 2.000(1) 1.998(2) 2.001(2) 2.001(2) 1.999(2) 1.999(2)
o
Y–O(3) 2.179(3) 2.187(3) 2.185(2) 2.185(2) 2.184(2) 2.184(2) 2.191(3) 2.179(3)
Y–O(6) ×2 1.989(2) 1.975(2) 1.978(1) 1.981(2) 1.977(2) 1.978(2) 1.978(2) 1.983(2)
<Y–O > 2.029 2.025 2.026 2.026 2.025 2.026 2.026 2.026
o
Z–O(3) 1.944(1) 1.939(1) 1.940(1) 1.941(1) 1.941(1) 1.941(1) 1.941(1) 1.943(1)
Z–O(6) 1.849(1) 1.853(2) 1.850(1) 1.849(1) 1.848(1) 1.851(1) 1.850(1) 1.849(1)
Z–O(7) 1.886(1) 1.887(1) 1.886(1) 1.885(1) 1.886(1) 1.887(1) 1.885(1) 1.887(1)
Z–O(7) 1.962(1) 1.963(1) 1.961(1) 1.961(1) 1.960(1) 1.963(1) 1.960(1) 1.961(1)
Z–O(8) 1.884(1) 1.888(1) 1.888(1) 1.889(1) 1.888(1) 1.887(1) 1.890(1) 1.885(1)
Z–O(8) 1.904(1) 1.899(1) 1.901(1) 1.901(1) 1.901(1) 1.901(1) 1.900(1) 1.902(1)
<Z–O>1.905 1.905 1.904 1.904 1.904 1.905 1.904 1.905
T–O(4) 1.628(1) 1.627(1) 1.627(1) 1.627(1) 1.627(1) 1.628(1) 1.627(1) 1.627(1)
T–O(5) 1.643(1) 1.642(1) 1.643(1) 1.643(1) 1.643(1) 1.643(1) 1.644(1) 1.643(1)
T–O(6) 1.594(1) 1.589(2) 1.591(1) 1.592(1) 1.592(1) 1.591(1) 1.591(1) 1.593(1)
T–O(7) 1.604(1) 1.602(1) 1.605(1) 1.605(1) 1.606(1) 1.604(1) 1.606(1) 1.604(1)
<T–O>1.617 1.615 1.617 1.617 1.617 1.617 1.617 1.617
B–O(2) 1.363(4) 1.361(4) 1.360(3) 1.359(3) 1.359(3) 1.363(3) 1.359(3) 1.361(3)
B–O(8) ×2 1.383(2) 1.383(2) 1.385(1) 1.385(2) 1.385(2) 1.385(2) 1.385(2) 1.386(2)
<B–O>1.376 1.376 1.377 1.376 1.376 1.378 1.376 1.378
_____________________________________________________________________________
______
FIG. 2. 11B MAS NMR spectra
of liddicoatite: (a) NMR 1;
(b) NMR 2; (c) NMR 3; (d)
NMR 4.
74 THE CAnADIAn mInErALoGIST
TABLE 4 (co nt’d ). INTERATOMIC D ISTANCES (Å ) IN L IDDICOATITE
__________________________________________________________________________________
_
L22 L23 L24 L25 L26 L27 L28
_______________________________________________________________________________
____
X–O(2) ×3 2.379(3) 2.380(2) 2.381(2) 2.387(2) 2.387(2) 2.383(2) 2.383(2)
X–O(4) ×3 2.780(3) 2.783(2) 2.783(2) 2.784(2) 2.783(2) 2.780(2) 2.784(2)
X–O(5) ×3 2.718(3) 2.716(2) 2.716(2) 2.720(2) 2.718(2) 2.719(2) 2.722(2)
<X–O>2.626 2.626 2.627 2.630 2.629 2.627 2.630
Y–O(1) 1.767(6) 1.773(4) 1.769(4) 1.768(4) 1.773(4) 1.770(4) 1.776(4)
d
Y–O(1) ×2 2.154(4) 2.158(3) 2.156(3) 2.169(3) 2.155(3) 2.160(3) 2.175(3)
d
Y–O(2) ×2 1.904(5) 1.899(3) 1.898(3) 1.895(3) 1.900(2) 1.894(3) 1.895(3)
d
Y–O(2) ×2 2.100(4) 2.108(2) 2.107(3) 2.110(3) 2.103(3) 2.110(3) 2.106(3)
d
Y–O(3) 2.182(3) 2.182(2) 2.186(2) 2.184(2) 2.190(2) 2.189(2) 2.176(2)
Y–O(6) ×2 1.978(2) 1.979(1) 1.979(1) 1.987(2) 1.985(2) 1.985(2) 1.990(1)
Y–O(1) 2.011(3) 2.016(2) 2.013(2) 2.020(3) 2.013(3) 2.016(2) 2.027(2)
o
Y–O(2) ×2 2.000(2) 2.001(1) 2.001(2) 2.000(2) 1.999(2) 2.000(2) 1.999(1)
o
Y–O(3) 2.181(3) 2.181(2) 2.185(2) 2.183(3) 2.187(3) 2.188(3) 2.175(2)
Y–O(6) ×2 1.977(2) 1.978(1) 1.979(2) 1.987(2) 1.985(2) 1.985(2) 1.989(2)
<Y–O > 2.024 2.026 2.026 2.030 2.028 2.029 2.030
o
Z–O(3) 1.941(1) 1.940(1) 1.940(1) 1.943(1) 1.943(1) 1.940(1) 1.942(1)
Z–O(6) 1.849(2) 1.849(1) 1.848(1) 1.848(1) 1.849(1) 1.848(1) 1.848(1)
Z–O(7) 1.886(2) 1.886(1) 1.885(1) 1.886(1) 1.885(1) 1.886(1) 1.885(1)
Z–O(7) 1.959(2) 1.962(1) 1.961(1) 1.962(1) 1.959(1) 1.962(1) 1.961(1)
Z–O(8) 1.888(2) 1.888(1) 1.889(1) 1.887(1) 1.887(1) 1.887(1) 1.887(1)
Z–O(8) 1.902(2) 1.900(1) 1.901(1) 1.902(1) 1.901(1) 1.901(1) 1.902(1)
<Z–O>1.904 1.904 1.904 1.905 1.904 1.904 1.904
T–O(4) 1.627(1) 1.627(1) 1.627(1) 1.628(1) 1.627(1) 1.627(1) 1.627(1)
T–O(5) 1.644(1) 1.644(1) 1.644(1) 1.644(1) 1.643(1) 1.643(1) 1.642(1)
T–O(6) 1.593(2) 1.592(1) 1.593(1) 1.592(1) 1.590(1) 1.592(1) 1.592(1)
T–O(7) 1.605(2) 1.604(1) 1.605(1) 1.605(1) 1.607(1) 1.604(1) 1.605(1)
<T–O>1.617 1.617 1.617 1.617 1.617 1.617 1.617
B–O(2) 1.358(4) 1.362(3) 1.359(3) 1.363(3) 1.354(3) 1.357(3) 1.362(3)
B–O(8) ×2 1.384(2) 1.385(2) 1.383(2) 1.385(2) 1.388(2) 1.386(2) 1.383(2)
<B–O>1.375 1.377 1.375 1.378 1.377 1.376 1.376
__________________________________________________________________________________
_
FIG. 3. 27Al MAS NMR spectra
of liddicoatite: (a) NMR 1;
(b) NMR 2; (c) NMR 3; (d)
NMR 4.
zonED LIDDICoATITE From AnJAnABonoInA, mADAGASCAr 75
0.08 and 0.01 apfu for slightly higher contents (~0.12
apfu). From this exercise, we may conclude that [4]B is
less than 0.02 and [4]Al is less than 0.01 apfu in all the
samples examined here.
57Fe Mössbauer spectroscopy
The Mössbauer spectra are shown in Figure 5.
As expected, the majority of the Fe in both sectors is
divalent, but a small amount of Fe3+ is present in each
sector: 9% and 5% in the pyramid and prism sectors,
respectively. There are two doublets assigned to Fe2+ in
octahedral coordination (Table 7), and their Mössbauer
hyperne parameters (Hawthorne 1988) are in accord
with the doublets Y1 and Y2 of Andreozzi et al. (2008),
which are assigned to Fe2+ at Y with different next-
nearest-neighbor arrangements.
SITE PoPULATIonS
Site populations were assigned on the basis of (1)
rened site-scattering values (Table 5), (2) the unit
formulae calculated from the electron-microprobe
analyses (Table 6), (3) the results of MAS NMR spec-
troscopy (Figs. 2 and 3), and (4) mean bond-lengths
(Table 4).
Renement of T-site scattering in tourmaline
We rened the T-site scattering by considering the
T site as occupied by Si and B, with the sum of their
occupancies constrained to unity. A key issue in such
a procedure is the type of scattering factors used for
the renement. In least-squares renement of a crystal
structure, the magnitudes of the calculated structure-
factors are scaled to the magnitudes of the observed
structure-factors by the scale factor, and there is a rela-
tively strong correlation between the scale factor and
the rened site-scattering factors. If all site-scattering
factors in a crystal structure are considered as variable,
the shift matrix becomes singular, and the renement
fails. It is necessary that the scattering for some of the
atoms in the structure be xed such that the rened
site-scattering values are correctly scaled, and the atoms
thus xed should constitute a signicant fraction of the
total scattering (preferably signicantly greater than
50%) in order that the scaling be reasonably accurate.
This scaling is affected by the type of scattering factors
used for the atoms, i.e., ionized or neutral. The total
scattering for an ionized species is less than that for a
neutral species for cations, and the inverse for anions.
Hence the type of scattering factors used will affect
the total rened site-scattering both directly through
the scattering factors of the rened species (usually
cations), and indirectly through the scattering factors of
the nonrened species (commonly anions). This issue
was investigated in detail for the structure of korneru-
pine, XM9T5O21(OH,F) where X = □, Fe2+, Mg; M =
Al, Mg, Fe2+, Fe3+; T = Si, Al, B (Cooper et al. 2009),
in which the three tetrahedrally coordinated T sites are
occupied by Si, Al and B. The scattering at the M sites
is ~1 epfu larger using an ionized scattering factor rather
than a neutral scattering factor for oxygen (Fig. 6a). The
site scattering at the partly occupied X site is in accord
with that determined by EMPA and SIMS for renement
with an ionized scattering factor for oxygen (Fig. 6b),
whereas the values determined using a neutral scattering
factor for oxygen deviate from the values determined by
EMPA–SIMS by ~1.1 epfu. These results suggest that
the rened values of B at the T site in tourmaline should
be sensitive to the type of scattering factors used. Here,
we have investigated the effects of the use of different
scattering curves on the renement of site-scattering
values in tourmaline, focusing on the occurrence of B
at the T site.
We refined all structures of liddicoatite in four
different ways under the constraint that Si + [4]B = 6
apfu, and obtained different values for the T-site occu-
pancy of [4]B for each different set of scattering factors
used. The results are summarized in Figure 7. Rene-
ment with ionized scattering-curves for O and Si failed
because renement converged toward negative occu-
pancy values for [4]B. In this case, we set the occupancy
of the T site to Si only and rened the occupancy, getting
values less than 1. We then recalculated the cations as
TABLE 5. S ITE-SCATTERING VALUES (epfu) FOR LIDDICOATITE
FROM MADAGASCAR, DERIVED FROM SREF AND EMPA
___________________________________________________________
X site Y site
__________________ __________________
SREF EMPASREF EMPA
___________________________________________________________
L1 16.9(1) 16.3 31.7(2 ) 32.0
L2 17.9(1) 17.3 28.7(2 ) 28.6
L4 17.2(1) 16.3 29.1(2 ) 29.0
L5 18.2(1) 17.7 26.5(2 ) 25.9
L6 18.3(1) 17.9 26.3(2 ) 25.4
L7 18.1(1) 17.5 25.6(2 ) 25.3
L11 16.9(1) 16.1 32.5(2 ) 32.9
L12 17.6(1) 16.8 30.5(2 ) 30.9
L13 16.3(1) 16.0 27.4(2 ) 27.1
L15 17.6(1) 17.2 23.8(3 ) 23.0
L16 17.6(1) 17.2 23.8(2 ) 24.1
L17 17.1(1) 16.7 25.0(2 ) 25.3
L18 17.5(1) 17.1 23.3(2 ) 23.9
L19 17.4(1) 17.1 23.8(2 ) 23.7
L20 17.4(1) 16.9 23.6(2 ) 23.9
L21 16.9(1) 16.4 25.5(2 ) 25.5
L22 17.3(1) 16.9 23.7(3 ) 24.0
L23 17.4(1) 17.1 23.8(2 ) 24.5
L24 17.8(1) 17.4 23.8(2 ) 23.9
L25 16.9(1) 16.3 25.4(2 ) 25.2
L26 17.1(1) 16.8 25.7(2 ) 26.9
L27 17.4(1) 16.2 25.2(2 ) 27.1
L28 17.2(1) 16.4 25.9(2 ) 23.9
<de v.> * 0.6 0.5
___________________________________________________________
* <dev.>: mean deviation.
76 THE CAnADIAn mInErALoGIST
zonED LIDDICoATITE From AnJAnABonoInA, mADAGASCAr 77
Si and B under the constraint that Si + B = 1, arriving
at small negative occupancy values for [4]B. The grand
mean [4]B content of the T site varies from –0.04 apfu
for ionized scattering-curves for O and Si to 0.25 apfu
for neutral scattering-curves for O and Si. No [4]B was
detected in the liddicoatite samples examined here by
11B MAS NMR, and the simulation results of Figure 4
suggests limits of detection of the order of 0.02 apfu.
This result is in accord with our renement results
using ionized scattering-curves for O and Si, suggesting
that use of these curves is giving more accurate results
for T-site populations than refinement with neutral
FIG. 4. 11B and 27Al MAS NMR spectra of liddicoatite
samples NMR1 [left, in both (a) and (b)] and NMR4
[right, in both (a) and (b)] with additional simulated peaks
added at the positions for (a) [4]B (~0 ppm) and (b) [4]Al
(~70 ppm) for various contents of [4]B and [4]Al in apfu
(indicated on the gure).
FIG. 5. Mössbauer spectra for liddicoatite: (a) prism sector; (b) pyramid sector.
78 THE CAnADIAn mInErALoGIST
scattering factors. Moreover, our renements using
neutral scattering factors for O and Si gave [4]B T-site
populations of ~0.25 apfu, values that should easily be
observed by 11B MAS NMR (see above).
The T site
In all MAS NMR spectra, there is no evidence of
[4]-coordinated B or Al in this crystal (Figs. 2, 3). These
results are in accord with the observed <T–O> bond
FIG. 6. Results for kornerupine; (a) comparison of the site-scattering at the [X +
M(1,2,4)] sites rened using ionized (O2–) and neutral (Oo) X-ray scattering factors;
(b) comparison of the X-site scattering derived by crystal-structure renement (SREF)
using an ionized scattering-factor for oxygen and the effective scattering calculated
from the unit formula derived from the electron-microprobe analysis; the dashed line
indicates the 1 : 1 relation, and the lines through the data points represent ±1 standard
deviation in this and the following gures. Modied from Cooper et al. (2009).
zonED LIDDICoATITE From AnJAnABonoInA, mADAGASCAr 79
FIG. 7. Variation in rened site-population for the T site in the liddicoatite fragments of
this work using the following scattering factors: (a) Si4+ and O2–; (b) Si4+ and O0; (c)
Si0 and O2–; (d) Si0 and O0.
80 THE CAnADIAn mInErALoGIST
lengths (Table 4), which range from 1.616 to 1.619 Å
(avg. = 1.6174 Å, <st.dev.> = 0.0007 Å). Hence, we
conclude that for this crystal, there are 6 Si apfu at the
T site. Formula normalization of the results of all the
chemical analyses done on this crystal yields a range
of values 5.90 < Si < 5.97 apfu with a mean value of
5.93 ± 0.02 apfu. Above, we concluded from the 11B
and 27Al MAS NMR spectra that [4]B is less than 0.02
apfu and [4]Al is less than 0.01 apfu in this crystal of
liddicoatite, indicating the Si should be greater than 5.97
apfu in these crystals. The difference between the mean
observed Si content of 5.93(2) apfu and the value of
5.97 apfu is 0.04(2) apfu, a value that is not signicantly
different from zero at the 99% condence limit. If we
assume a Si value of 6.00 apfu in these crystals, the
difference between the average observed value and our
assumed value is 0.07(2) apfu, a value that is marginally
signicant at the 99% condence limit. Incorporation
of small amounts of [4]B or [4]Al at the T sites would
change the <T–O> distances by less than 0.002 Å, of the
same order of magnitude as the standard deviations on
the distances, and hence provide no evidence of devia-
tion from 6.00 Si apfu. The observed <T–O> distances
are in the range 1.616–1.619 Å, close to the ideal
<TSi–O> distance (in the tourmaline structure), 1.620
Å, given by MacDonald & Hawthorne (1995).. Thus we
presume that there is a small but systematic error (that
we have been unable to nd) in our electron-microprobe
data and assign our T-site occupancies as 6.00 Si apfu.
Ertl et al. (2006) reported structure and chemical
data on four fragments of a crystal of liddicoatite
from Anjanabonoina, Madagascar. They analyzed the
crystals for B by SIMS and reported 0.14–0.57 apfu
[4]B. This amount of [4]B would easily be detected by
11B MAS NMR, and hence we must conclude that the
two samples of liddicoatite differ signicantly in their
T-site contents.
TABLE 6. C HEMICAL COMPOSITIONS AND UNIT F ORMULAE OF LIDDICOATITE
_________________________________________________________________________________
L1 L2 L4 L5 L6 L7 L11 L12 L13 L15 L16
_________________________________________________________________________________
2
SiO wt.% 36.81 37.01 37.30 37.25 37.28 37.63 36.88 36.59 37.69 37.98 37.43
2
TiO 0.03 0.01 0.02 0.01 0.01 0.02 0.00 0.01 0.08 0.01 0.02
23
Al O38.35 38.08 38.24 38.19 38.25 38.82 37.83 37.70 38.87 39.35 39.08
23
B O 10.85 10.84 10.92 10.88 10.89 11.01 10.81 10.74 11.05 11.11 10.99
23
Fe O0.07 0.01 0.06 0.01 0.01 0.03 0.02 0.02 0.13 0.02 0.04
FeO 0.76 0.11 0.63 0.15 0.14 0.32 0.18 0.18 1.38 0.21 0.42
MgO 0.00 0.00 0.43 0.00 0.00 0.01 0.00 0.00 0.26 0.00 0.00
MnO 2.67 2.42 1.74 1.54 1.34 1.00 3.89 3.09 0.25 0.24 0.26
CaO 2.84 3.28 3.03 3.67 3.75 3.76 2.56 2.94 3.46 4.15 4.04
PbO 0.50 0.60 0.48 0.53 0.53 0.46 0.58 0.59 0.14 0.23 0.24
2
Na O 1.40 1.14 1.25 0.96 0.93 0.92 1.51 1.30 1.13 0.75 0.80
2
Li O2.00 2.26 2.18 2.47 2.50 2.51 1.98 2.09 2.36 2.67 2.54
2
H O 3.08 3.09 3.21 3.10 3.10 3.12 3.10 3.01 3.19 3.19 3.14
F1.40 1.37 1.17 1.39 1.38 1.42 1.34 1.47 1.30 1.35 1.37
O=F –0.59 –0.58 –0.49 –0.59 –0.58 –0.60 –0.56 –0.62 –0.55 –0.57 –0.58
Ó100.17 99.64 100.17 99.56 99.53 100.43 100.12 99.11 100.74 100.69 99.79
Si apfu 5.895 5.933 5.937 5.948 5.948 5.942 5.927 5.921 5.931 5.944 5.921
4+
B3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000
3+
Al 6.000 6.000 6.000 6.000 6.000 6.000 6.000 6.000 6.000 6.000 6.000
3+
Ti 0.004 0.001 0.002 0.001 0.001 0.002 0.000 0.001 0.009 0.001 0.002
4+
Al 1.238 1.194 1.174 1.187 1.193 1.224 1.166 1.190 1.209 1.258 1.286
3+
Fe 0.009 0.001 0.007 0.002 0.002 0.004 0.002 0.002 0.016 0.002 0.005
3+
Fe 0.101 0.015 0.084 0.019 0.018 0.042 0.025 0.025 0.181 0.027 0.055
2+
Mg 0.000 0.000 0.102 0.000 0.000 0.002 0.000 0.000 0.061 0.000 0.000
2+
Mn 0.362 0.329 0.235 0.208 0.181 0.134 0.530 0.424 0.033 0.032 0.035
2+
Li 1.286 1.460 1.396 1.583 1.605 1.592 1.277 1.358 1.491 1.680 1.617
+
ÓY3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000
Ca 0.487 0.563 0.517 0.628 0.641 0.636 0.441 0.510 0.583 0.696 0.685
2+
Na 0.435 0.354 0.386 0.297 0.288 0.282 0.471 0.408 0.345 0.228 0.245
+
Pb 0.022 0.026 0.021 0.023 0.023 0.020 0.025 0.026 0.006 0.010 0.010
2+
0.056 0.057 0.076 0.052 0.048 0.062 0.063 0.056 0.066 0.066 0.060
ÓX1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000
OH 3.291 3.306 3.411 3.298 3.304 3.291 3.319 3.248 3.353 3.332 3.315
–
F0.709 0.694 0.589 0.702 0.696 0.709 0.681 0.752 0.647 0.668 0.685
–
Ó(V+W)4.000 4.000 4.000 4.000 4.000 4.000 4.000 4.000 4.000 4.000 4.000
_________________________________________________________________________________
zonED LIDDICoATITE From AnJAnABonoInA, mADAGASCAr 81
<T–O> versus site occupancy
Ertl et al. (2006) rened the occupancies of T-site B
in four crystals of elbaite–liddicoatite from Madagascar
and presented a relation between the rened [4]B content
and the corresponding <T–O> values (Fig. 8a). The
correlation coefcient given for the relation shown in
Figure 8a is 0.984, and the standard error of estimate
is 0.001 Å. In considering the agreement between
observed data and a model, the deviations of the data
from their ideal values of that model should follow a
normal distribution. We may examine the deviations
between the measurements and their ideal values using
half-normal probability-plot analysis (Abrahams 1972,
1974, Abrahams & Keve 1971). If the weighted devia-
tions from the ideal values are drawn from a normal
distribution, the ranked weighted observed differences,
D/sD, should be linear, with the expected normal distri-
bution (dened for small samples by Hamilton & Abra-
hams 1972), and have a slope of unity and an intercept
of zero. Figure 8b shows the resulting relation for the
data of Figure 8a; the data are linear but the slope of
the relation is 0.12, a factor of ~8 less than the correct
value of 1.0. The origin of the error in this type of plot
may come from (1) erroneous assignment of standard
deviations; (2) some systematic bias in the data. The
origin of this bias is not clear. However, what is clear
is that this relation between <T–O> and [4]B content
cannot be considered as rmly established.
Two other relations between <T–O> and site popula-
tions have been presented: (1) <T–O> versus [4]Al for
a series of uvite samples (MacDonald & Hawthorne
1995), and (2) <T–O> versus [4]B for a series of tour-
maline samples (Hughes et al. 2004). Hughes et al.
(2004) expressed <T–O> solely as a function of [4]B
where the assigned T-site populations also contain [4]Al
TABLE 6 (co nt’d ). C HEMICAL COMPOSITIONS AND UN IT FORMULAE OF LIDDICOATITE
_________________________________________________________________________________
L17 L18 L19 L20 L21 L22 L23 L24 L25 L26 L27 L28
_________________________________________________________________________________
2
SiO wt.% 37.45 37.35 37.50 37.77 37.62 37.71 37.12 37.64 38.16 37.33 37.19 37.36
2
TiO 0.04 0.02 0.02 0.02 0.06 0.03 0.03 0.01 0.06 0.08 0.14 0.10
23
Al O39.21 39.36 39.20 39.58 39.04 38.99 39.06 39.33 38.71 38.25 38.86 38.57
23
B O 11.01 10.99 11.00 11.10 11.03 11.04 10.94 11.05 11.10 10.89 10.95 10.97
23
Fe O0.07 0.02 0.03 0.04 0.09 0.04 0.04 0.03 0.08 0.06 0.10 0.08
FeO 0.78 0.24 0.32 0.37 0.92 0.45 0.39 0.26 0.85 0.65 1.08 0.86
MgO 0.00 0.00 0.00 0.01 0.06 0.11 0.09 0.00 0.25 0.00 0.07 0.29
MnO 0.23 0.24 0.21 0.18 0.23 0.26 0.25 0.35 0.45 0.42 0.43 0.52
CaO 3.81 4.06 4.03 4.12 3.78 4.05 4.08 4.06 3.64 3.86 3.61 3.71
PbO 0.21 0.20 0.20 0.14 0.13 0.15 0.17 0.30 0.16 0.12 0.13 0.17
2
Na O 0.92 0.78 0.81 0.77 0.93 0.81 0.78 0.78 1.06 0.88 1.01 1.10
2
Li O2.45 2.51 2.56 2.56 2.47 2.58 2.45 2.56 2.56 2.57 2.32 2.39
2
H O 3.12 3.10 3.16 3.18 3.17 3.20 3.13 3.13 3.20 3.35 3.18 3.13
F1.43 1.46 1.34 1.37 1.34 1.28 1.35 1.43 1.34 0.86 1.26 1.38
O=F –0.60 –0.61 –0.56 –0.58 –0.56 –0.54 –0.57 –0.60 –0.56 –0.36 –0.53 –0.58
Ó100.13 99.72 99.82 100.63 100.31 100.16 99.31 100.33 101.06 98.96 99.80 100.05
Si apfu 5.913 5.906 5.923 5.916 5.929 5.939 5.899 5.922 5.973 5.956 5.904 5.919
4+
B3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000
3+
Al 6.000 6.000 6.000 6.000 6.000 6.000 6.000 6.000 6.000 6.000 6.000 6.000
3+
Ti 0.005 0.002 0.002 0.002 0.007 0.004 0.004 0.001 0.007 0.010 0.017 0.012
4+
Al 1.297 1.335 1.297 1.307 1.251 1.238 1.316 1.293 1.141 1.193 1.271 1.202
3+
Fe 0.009 0.003 0.004 0.004 0.011 0.005 0.005 0.003 0.010 0.008 0.012 0.010
3+
Fe 0.102 0.031 0.042 0.049 0.121 0.059 0.052 0.035 0.111 0.086 0.143 0.114
2+
Mg 0.000 0.000 0.000 0.002 0.014 0.026 0.021 0.000 0.058 0.000 0.017 0.068
2+
Mn 0.031 0.032 0.028 0.024 0.031 0.035 0.034 0.047 0.060 0.057 0.058 0.070
2+
Li 1.556 1.597 1.627 1.612 1.565 1.633 1.568 1.621 1.613 1.646 1.482 1.524
+
ÓY3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000
Ca 0.645 0.688 0.682 0.691 0.638 0.683 0.695 0.684 0.610 0.660 0.614 0.630
2+
Na 0.282 0.239 0.248 0.234 0.284 0.247 0.240 0.238 0.322 0.272 0.311 0.338
+
Pb 0.009 0.009 0.009 0.006 0.006 0.006 0.007 0.013 0.007 0.005 0.006 0.007
2+
0.064 0.064 0.061 0.069 0.072 0.064 0.058 0.065 0.061 0.063 0.069 0.025
ÓX1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000
OH 3.286 3.270 3.331 3.321 3.332 3.362 3.322 3.288 3.337 3.566 3.367 3.309
–
F0.714 0.730 0.669 0.679 0.668 0.638 0.678 0.712 0.663 0.434 0.633 0.691
–
Ó(V+W)4.000 4.000 4.000 4.000 4.000 4.000 4.000 4.000 4.000 4.000 4.000 4.000
_________________________________________________________________________________
82 THE CAnADIAn mInErALoGIST
and [4]Be, and so the status of this relation is not clear.
MacDonald & Hawthorne (1995) did not consider the
possible presence of [4]B in their uvite samples, but
Lussier et al. (2009) did not detect any [4]B in these
samples by 11B MAS NMR.
Here, we examine the variation in <T–O> as a
function of constituent cation radius (from Shannon
1976) as the effect of each cation is incorporated into
the aggregate radius at the T site for each structure.
Figure 9 shows the resultant relation for structures
from MacDonald & Hawthorne (1995), Schreyer et al.
(2002), Hughes et al. (2000, 2001, 2004), Ertl & Hughes
(2002), Ertl et al. (1997, 2003a, 2003b, 2004, 2005,
2006, 2007), Marschall et al. (2004) and Cempírek et
al. (2006). What is immediately apparent is that the
close ts to linear models presented by MacDonald
& Hawthorne (1995), Hughes et al. (2004) and Ertl et
al. (2006) are not all mutually compatible. Moreover,
it is also apparent that the site populations given for
several structures are not compatible with the observed
mean bond-lengths: For example, the olenite of Ertl et
al. (1997) (with [4]B = 1.225 apfu) has a much larger
[4]B content than the olenite of Ertl et al. (2007) (with
[4]B= 0.660 apfu) and yet has a considerably longer
mean bond-length: 1.610 versus 1.604 Å. Ertl et al.
(2007) updated the T-site population of the olenite
reported by Ertl et al. (1997) from (Si4.775B1.225) to
(Si4.89B0.83Al0.27Be0.01), but this proposal is difcult to
evaluate, as no new chemical data or structural results
are given to justify this reassignment. The scatter of the
data in Figure 9 does not warrant doing a least-squares
t. The dashed line was drawn through the data by
eye, and the dotted line was drawn through the data of
MacDonald & Hawthorne (1995) (no [4]B, T = Si,Al
only) with a slope of ~1. These two lines diverge at
low aggregate radii (large [4]B values), emphasizing that
we need some reliable data for high-[4]B tourmalines in
order to tie down the lower end of the trends suggested
by Figure 9.
The Z site
Hawthorne et al. (1993) showed that Al and Mg can
be partly disordered over the Y and Z sites. MacDonald
& Hawthorne (1995) showed that Mg may occur at the
Z site in uvite (ideal formula Ca YMg3 Z(Al5Mg) Si6O18
(BO3)3 (OH)3F; Hawthorne & Henry 1999). Trivalent
Cr is partly disordered over the Y and Z sites (Bosi et
al. 2004). Taylor et al. (1995) showed that incorporation
of O2– at the O(1) site can drive disorder of divalent
and trivalent cations over the Y and Z sites. Thus it has
been established that Al, Fe3+, Cr3+ and Mg can occur
at the Z site. The situation for Fe2+ is more contro-
versial. Hawthorne et al. (1993) originally considered
the disorder of Mg and Al over the Y and Z sites. The
decision to restrict disorder to Mg and Al only was not
based on crystal-chemical reasons; they stated that it
was done this way because there was no information
TABLE 7. M ÖSSBAUER PARAMETERS FOR LIDDICOATITE
___________________________________________________________
ä (mm/s) Ä (mm/s) Ã (mm/s) Re l. area (%)
___________________________________________________________
(x = 0 .62) Prism
2
Fe 1.080(12) 2.48(5) 0.30(2) 72(34)
2+
Fe 1.12(4) 2.23(17) 0.30(8) 23(35)
2+
Fe 0.26(11) 0.31(18) 0.28* 5(2)
3+
(x = 0.54) Pyramid
2
Fe 1.081(8) 2.44(2) 0.29(2) 74(14)
2+
Fe 1.14(13) 1.81(45) 0.43(19) 17(18)
2+
Fe 0.31(12) 0.27(15) 0.28(12) 9(4)
3+
___________________________________________________________
* fixed p arame ter.
FIG. 8. (a) The relation between <T–O> and [4]B content
from Ertl et al. (2006); (b) half-normal probability plot for
the data of Figure 8a; the broken line shows the correct
relation, and the dotted line shows a least-squares t to
the data.
zonED LIDDICoATITE From AnJAnABonoInA, mADAGASCAr 83
available on site scattering apart from the fact that
previous renements had been done with Z = Al6 apfu.
For tourmalines of the schorl–dravite series, Bloodaxe
et al. (1999) stated that their rened site-scattering
values for the Z site lie in the range 12–13 e (although
they did not give the specic values, and did not state
what type of scattering factors they used to rene their
structures). Accordingly, they assigned only Mg and Al
to the Z site for these structures. Conversely, for tour-
malines of the schorl–dravite series, Bosi & Lucchesi
(2004) reported rened Z-site scattering values in the
range 12.87(5)–13.48(7) e and assigned small amounts
of Fe2+ to the Z site in some (but not all) structures of
this series. Finally, Bosi (2008) and Andreozzi et al.
(2008) put forward a persuasive case for partial disorder
of Fe2+ over the Y and Z sites in some tourmalines of
the schorl–dravite series. What is certain from the above
discussion is that other cations in addition to Al can
occur at the Z site in the tourmaline structure.
For the crystals of this study, if allowed to vary
during renement, the Z site rened to complete Al
occupancy, and it was xed as such in the nal stages of
renement. Equivalent isotropic-displacement param-
eters are in accord with equal scattering at the Z site in
all of the structures rened here [Ueq = 0.0061(5)], and
the <Z–O> distances are 1.905 ± 0.001, showing no
signicant variation in any of these structures. More-
over, the grand <Z–O> distance of 1.905 Å and the
mean c parameter (~7.11, Table 1) are in close accord
with the corresponding curve of Bosi (2008). We thus
conclude that the Z site is completely occupied by Al
in these structures.
The Y site
Comparison of compositional and structural data
conrms that the Y sites are occupied by Li, Al, Fe2+,
and Mn2+, with minor-to-trace amounts of Ti4+ and
Mg. In all samples analyzed, the mean absolute devia-
tion between the rened site-scattering values and the
analogous value derived from the unit formulae is 0.5
e per site, indicating very close agreement between
the formula-normalization procedure and the proposed
site-assignments. The variation in <Y–O> distances with
the aggregate radius of the constituent Y-site cations is
linear, with no signicant deviations (Fig. 10).
The X site
The formulae derived from the chemical composi-
tions (Table 4) have Na, Ca and Pb assigned to the X
FIG. 9. Variation in <T–O> as a function of constituent-cation radius for selected data
from the literature (see text). White circles: Hughes et al. (2000, 2001), Schreyer et al.
(2002), Ertl & Hughes (2002), Ertl et al. (2003a, 2003b), Marschall et al. (2004), Ertl et
al. (2005), Cempírek et al. (2006); black circles: Hughes et al. (2004); black diamonds:
MacDonald & Hawthorne (1995); black triangle: Ertl et al. (2007); inverted white
triangles: Lussier et al. (2008); black squares: Ertl et al. (2006); white squares: Ertl et
al. (1997), Hughes et al. (2000); white diamond: grand mean value for the 26 structures
of the present study. Dashed line: drawn as a guide to the eye through all the data; dotted
line: drawn as a guide to the eye through the data of MacDonald & Hawthorne (1995).
84 THE CAnADIAn mInErALoGIST
site. The X site is almost completely lled, with vacan-
cies that are consistently less than 0.10 pfu.
W and V sites
For any tourmaline, the occupancy of the W posi-
tion [≡ O(1) site] in the general formula is [(OH)xFy
O1–x–y], where 0 ≤ x, y ≤ 1 (and x + y ≤ 1), and the
occupancy of the V position [≡ O(3) site] is [(OH)xO3–x]
where 0 ≤ x ≤ 3. The occurrence of F at V has not been
shown to occur (see Hawthorne & Henry 1999). For
the Madagascar liddicoatite crystals analyzed here, the
structural formulae (Table 6) are calculated on the initial
assumption that W(OH) + WF = 1 apfu and V(OH) = 3
apfu, and hence (OH) + F = 4 apfu. By calculating the
average sums of bond valences at the O(1) and O(3)
sites for each crystal, the validity of these assumptions
can be assessed.
Consider rst the occupancy of the O(1) site, which
is bonded to the three Y-site cations. For a tourmaline
where WF = 1 apfu or WO = 1 apfu, the sum of bond
valences incident from the Y-site cations must be ~1.0
and ~2.0 vu, respectively. Where W(OH) = 1.00 apfu,
the sum of bond valences on the oxygen ion is ~1.2 vu,
with the remaining ~0.8 vu incident from the H ion. If
the assumption that W(OH) + WF = 1 apfu is correct,
the average sum of bond valences at O(1) is expected
to be between 1.00 and 1.20 vu. Table 6 shows that
for all the analyzed crystals, the average occupancy
of the W site is [F0.671(OH)0.329], with relatively little
variance (s = 0.062 apfu). The expected bond-valence
sum may be derived as a linear combination of these
two components: this gives a value of ~1.06 vu.
Table 8 shows bond-valence sums at the O(1) site for
each crystal, calculated using the curves of Brown &
Altermatt (1985) and the observed bond-lengths for the
disordered O(1) position (Table 4). Here, the calculation
is weighted assuming a random distribution of Y–WF
bonds in each sample. Cations with smaller radii (such
as Al: 0.535 Å) are assigned to the shorter Y–O(1) bond,
whereas cations with larger radii (such as Li: 0.76,
Fe2+: 0.78 and Mn2+: 0.83 Å) are assigned to the longer
Y–O(1) bond. Calculated values vary between 0.96 and
1.05 vu, with an average value of 1.01 vu. This value is
in reasonable accord with the predicted value, validating
the assumption that W(OH) + WF = 1 apfu.
Similarly, for the O(3) site, incident bond-valence
sums are also listed in Table 8. These vary between 1.10
and 1.11 vu, with an average of 1.11 vu. Although lower
than the ideal value of 1.20 vu expected for full (OH)
occupancy, these values clearly indicate no substantial
amount of VO to be present in these crystals, validating
the assumption that V(OH) = 3 apfu.
ConCLUSIon
Extensive crystal-structure refinement and 11B
and 27Al Magic-Angle-Spinning Nuclear Magnetic
Resonance spectroscopy have given no evidence of
the presence of tetrahedrally coordinated B or Al at
the T site throughout the oscillatory zoned crystal of
liddicoatite examined here, and hence Si is equal to 6.00
apfu throughout the crystal. The <Z–O> distances and
equivalent isotropic-displacement parameters show no
FIG. 10. Variation in <Y–O> as a function of the aggregate radius of the cations at the Y
site in liddicoatite.
zonED LIDDICoATITE From AnJAnABonoInA, mADAGASCAr 85
signicant variation throughout these structures, and are
in accord with complete occupancy of the Z site by Al;
thus ZAl is equal to 6.00 apfu throughout the crystal. We
may thus conclude that the oscillatory character of this
crystal, which is further characterized by Lussier et al.
(2011) in an accompanying paper, arises from chemical
variations solely at the X and Y sites.
ACknoWLEDGEmEnTS
The authors thank Ferdinando Bosi, Andreas
Ertl, Guest Editor Horst Marschall and E.B. for their
comments on this paper. We are grateful to Carl Francis,
Curator of the Harvard University Mineralogical
Museum, for supplying us with this sample. The work
was funded by a Canada Research Chair in Crystal-
lography and Mineralogy to FCH, and by a Major
Facilities Access Grant, Research Tools and Equipment,
and Discovery Grants to FCH and SK from the Natural
Sciences and Engineering Research Council of Canada,
and by Canada Foundation for Innovation Grants to
FCH and SK. Assistance was also provided by funding
to AJL in the form of a summer undergraduate NSERC
research award, and to AJL and VKM in the form of
NSERC Postgraduate Scholarships. Access to the 900
MHz NMR spectrometer was provided by the National
Ultrahigh-Field NMR Facility for Solids (Ottawa,
Canada), a national research facility funded by the
Canada Foundation for Innovation, the Ontario Innova-
tion Trust, Recherche Québec, the National Research
Council of Canada, and Bruker BioSpin, and managed
by the University of Ottawa (www.nmr900.ca). The
Natural Sciences and Engineering Research Council
of Canada is acknowledged for a Major Resources
Support grant.
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TABLE 8. BOND-VALENCE SUMS AT O(1 ) AND O (3) P OSITIONS
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___________________________________________________________
O(1)O(3)O(1)O(3)
Sam ple ÓsÓsS am ple ÓsÓs
___________________________________________________________
L1 1.00 1.11 L18 1.01 1.10
L2 0.98 1.11 L19 1.02 1.10
L4 1.02 1.11 L20 1.03 1.10
L5 0.97 1.11 L21 1.02 1.10
L6 0.97 1.10 L22 1.02 1.10
L7 0.98 1.11 L23 1.02 1.11
L11 0.98 1.11 L24 1.01 1.10
L12 0.96 1.11 L25 0.97 1.10
L13 1.02 1.11 L26 1.05 1.10
L15 1.01 1.10 L27 1.05 1.11
L16 1.01 1.10 L28 0.98 1.11
L17 1.03 1.10 <vu>1.01 1.11
___________________________________________________________
The bond-valence sum s are expressed in valence units (vu).
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Received February 2, 2010, revised manuscript accepted
November 30, 2010.
