Mg. Mg. Al. 3817 cm-1. K. W(O1). V(O3). Structural accommodation of K at dravitic ... EJ Berryman1,2*, B Wunder1, A Ertl3,4, M Koch-Müller1, D Rhede1, K Scheidl4, G Franz2, W Heinrich1 ... 2 Department of Mineralogy and Petrology, Technical University of Berlin, Germany ... Raman Spectroscopy: OH-stretching region.
Structural accommodation of K at dravitic tourmaline’s X site: Insight from Raman spectroscopy and single crystal X-ray diffraction EJ Berryman1,2*, B Wunder1, A Ertl3,4, M Koch-Müller1, D Rhede1, K Scheidl4, G Franz2, W Heinrich1 1 Chemistry and Physics of Earth Materials (Section 3.3), GeoForschungsZentrum (GFZ) Potsdam, Germany 2 Department of Mineralogy and Petrology, Technical University of Berlin, Germany 3 Mineralogisch-Petrographische Abt., Naturhistorisches Museum, Vienna, Austria 4 Institute for Mineralogy and Crystallography, Geozentrum, University of Vienna, Austria
Objectives Background:
X O4
O5 O4
O5 T
Results and Discussion
Tourmaline has the general structural formula:
O5 O4
XY3Z6T6O18(BO3)3V3W where
H1
X=
[9]
Y = Mg , Fe , Al , Fe , Cr , Mn , Li 2+
3+
2+
+
4+
3+
H3
H3
K
Na
X O5
O4
O5 O4
2-
Ionic radii: 1.55 Å
MF2 100 μm
1.24 Å
7.125 Å Ca
K is typically a trace element in tourmaline, occupying less than 10% of the X site. However, its presence in Mg-Al tourmaline increases with pressure (Berryman et al. 2015), leading to the formation of the K-dominant tourmaline endmember maruyamaite at UHP conditions.
Z
Y
X
O5
O5
O3
O3
O4
a
X
Magnesio-foitite
X
Z
a
Tourmaline structure viewed down the c axis.
Maruyamaite EB13
Dravite EB28
Dravite EB29
Magnesiofoitite MF2
P T
4.0 GPa 700°C
4.0 GPa 600°C
4.0 GPa 600°C
0.4 GPa 700°C
K Na
0.70(4) 0.03(2) 0.27(5) 2.58(12) 6.34(12) 5.83(8) 3.25(13) 3.92(6) 0.03(6)
0.02(0) 0.81(3) 0.17(3) 2.41(14) 6.42(15) 5.47(21) 3.70(22) 3.83(16) 0.03(6)
0.03(1) 0.63(5) 0.34(5) 2.50(20) 6.33(18) 5.50(20) 3.67(19) 3.66(22) 0.00(1)
0.00(1) 0.01(2) 0.98(2) 1.94(15) 7.11(29) 5.73(25) 3.22(20) 3.78(23) 0.02(4)
Mg Al Si B OH O
Site V
O1
O7
O6
Y O3
O5
O2
Maruyamaite EB13
Magnesio-foitite MF2
K0.76(3) Mg1.00 Al1.00 B3.00 Si5.4B0.6(1)
Na0.09(6) Al1.62Mg1.38(18) Al4.92Mg1.08(24) B3.00 Si5.66B0.34(4)
X Y Z B T
W
(Mg2Al)ZAl6TSi6O18(BO3)3V(OH)3W(OH)
Synthesis conditions & Compositions of synthesized tourmalines (EMPA) pfu
T
O6
O8
Z O3
O2
O8
cf.
Site occupancies determined by SREF
NaYMg3ZAl6TSi6O18(BO3)3V(OH)3W(OH) Y
V =1571.7 Å
O7
SREF details R index Reflections Maruyamaite (EB13) 4.88% 2083 Magnesio-foitite (MF2) 1.19% 5578
Maruyamaite Magnesio-foitite Bond MF2 EB13 2.737(12) 2.009(11) 1.992(1) 1.931(8) 1.920(1) 1.615(6) 1.616(1) 1.37(2) 1.376(1) Arrows indicate whether the value is increased or decreased relative to the literature values below.
Largest bondlength measured Bloodaxe et al. (1999) was 2.696(5) Å for dravitic tourmaline with an average X-site occupancy of 0.540(52) Na, 0.027(2) Ca, and 0.025(31) K pfu.
bondlength of 1.926 Å for Z site occupied by Al4.977Mg1.023 (Bloodaxe et al. 1999)
Mg
c
3300 3400 3500 3600 3700 3800
c
Dravite (EB29)
3577
coe EB28 10 μm
Dravite (EB29)
The lattice vibrations of magnesio-foitite are distinct from dravite and maruyamaite.
tur Magnesio-foitite (MF2)
3513 3622 3641
Assign.
3817 3776-3780 3769 O1 3740-3741 3657 3636-3641 3618-3622
KYMg3 X NaYMg3 X Y K Mg2Al X NaYMg2Al X Y Mg3 Y X Mg2Al X Y MgAl2
MF2 100 μm
400
600
800
1000
3776
Mg
3300 3400 3500 3600 3700 3800
Dravite (EB28)
c
3576 3550 3500
Mg
Mg
Mg
3618 3640 3741
Mg
Mg
Na
OH Band (cm-1)
Assign. X
H1
3657 O1 3636-3641 3618-3622
O1
Al
Mg
Mg
Mg
X
X
H1
H1
Al
3618 -3622 cm-1
Mg
c
Magnesio-foitite (MF2)
3459 3511 3551
Al
Al O3
3619 3657
Mg
Al
Mg
Mg
Al
H3
3500-3520 cm-1
3550 - 3558 cm-1
Raman shift (cm ) -1
The authors are grateful for the assistance of H-P Nabein in generating the powder XRD data and conducting the hydrothermal synthesis experiment of MF2, as well as U Dittmann for preparing the samples for EMPA. This study was supported by funding from the DFG granted to GF and WH (FR 557/31-1; HE 2015/16-1). EB is grateful for a post-graduate scholarship awarded by NSERC.
X
3551 3511 3459
Mg2Al YZ MgAl2 YZ Al3 YZ
1.9 1.1 1.54 0.77 0.89 1.79 0 4.01
3 2 1
0 1 2
42%
1.27
58%
0.58 1.16
2 1 0
1 2 3
15% 42% 43%
Y and Z sites composition EMPA
1.9
0
1.1
0.93 0.46 1.25 2.49 0 3.87 2.4 2.6
6.6 6.3
7%
0.22
0
43%
0.87 0.43
56%
1.12
0.56
35% 22%
0.71 0.35 0.21 0.43
12% 25%
0.23 0.25
0.11 0.50
27% 29% 44%
1.8 1.60 0.88 0
1.2 0.80 1.76 3.96
36% 28% 36%
1.8 2.13 0.84 0
1.2 1.06 1.69 3.28
2.5 2.4
6.5 6.4
3.0 2.5
6.0 6.3
6.6 6.3
Magnesio-foitite (MF2) Mg/ Al/ Al occurrence occurrence Rel. Area Mg
Al
The composition of the Y and Z sites is calculated from the integrated peak intensity of each assigned band. Bands assigned to the O1 site provide the Y site composition; bands assigned to the O3 site, the net Mg/Al ratio of the Y and Z sites. The latter can be compared to the value obtained by EMPA. In an ideal ordered tourmaline, Mg preferentially occupies the Y site and Al the Z site. These calculations demonstrate that the amount of Mg-Al disorder between the Y and Z sites can be quantified with Raman spectroscopy.
Magnesio-foitite has demonstrable variations in the bonding environment around the other crystallographic sites, leading to distinct differences in its low frequency Raman spectrum. Magnesio-foitite’s long-range structural differences affect the O3-H3 bond, shifting the associated Raman bands to lower wavenumbers. However, the band positions of vibrations assigned to the O1-H1 bond were consistent with maruyamaite and dravite.
Mg
Al
H3
3576 - 3579 cm-1
Decreasing Raman shift = Decreasing energy of O-H bond
0.51 0.25 0.14 0.27
Mg
A vacant X site leads to the lengthening of the H1-O1 bond.
O3
O3
H3
3300 3400 3500 3600 3700 3800
Mg
25% 14%
Rel. Area
With K incorporation, the expanded X site impinges on the hydroxyl in the O1 site leading to its shortening. The other sites in the crystal structure are not measurably affected.
O3-H3 Band Assignments Al
1.13 0.56
2.4 2.6
Al
0
56%
Y site composition 1 26% 2 30% 3 44%
Mg
Tourmaline’s crystal structure expands with increasing the size of the X-site-occupying ion.
3657 cm-1
3636 -3641 cm-1
X
Mg3 Y Mg2Al Y MgAl2 Y
0.15
Rel. Area
Dravite (EB29)
Raman spectroscopy of compositionally restricted synthetic tourmaline facilitates band assignments and allows the calculation of the Mg-Al ratio in the Y and Z sites.
O1
Al
5%
Dravite (EB28)
Conclusions
H1
O1
Mg
2 1 0
0 0 1 1 0 1 2
Y site composition
X
Mg
Mg2Al YZ MgAl2 YZ Al3 YZ
3 3 2 2 3 2 1
3817 cm-1
3776-3780 cm-1
Al
X
Maruyamaite (EB13) Mg/ Al/ Al occurrence occurrence Rel. Area Mg
Y and Z sites composition EMPA
3740-3741 cm-1
O1
1200
Acknowledgements:
Al
Mg
O3
Raman shift (cm )
EB29 10 μm
OH Band (cm )
3576-3579 O3 3550-3558 3500-3520
3740
-1
200
O1
O1
O1
3300 3400 3500 3600 3700 3800
The size of the X-site-occupying ion (K vs Na) does not have an influence on the lattice vibrations.
H1
H1
3549
3780
Maruyamaite(EB13)
H1
Na
676 688
Maruyamaite (EB13) and dravite (EB29) have identical spectra in this range.
K
3769 cm-1
Raman spectra in the 100 - 1200 cm-1 provide information about the lattice vibrations in tourmaline.
tur
tur
3769 3817
3618 3636
bondlength of ~1.62 Å for T site fully occupied by Si
tur
EB13 10 μm
Maruyamaite (EB13)
Raman Spectroscopy: Lattice vibrations 228 267 311
K
bondlength of 2.044 Å for Y site dominated by Mg (Pertlik et al. 2003)
0.91
Italicized values fixed in refinement.
Synthesis Details: The tourmalines were synthesized in sealed gold capsules from an oxide mixture of MgO, γ-Al2O3, SiO2, H3BO3, and a KCl-NaCl or pure H2O fluid in a piston-cylinder press (4.0 GPa) or hydrothermal pressure apparatus (0.4 GPa). MF2 was synthesized using the two-chamber method of von Goerne et al. (1999) to produce large crystals.
B
c
Dravite
Y
O6 O4
O4
O5
K Mg3 Al6 Si6O18(BO3)3 (OH)3 (OH)
Maruyamaite
X
O2
X
O4
W(O1)
V =1588.1 Å3
Mean bondlengths (Å) determined by SREF
Intensity
T
O2
O2
Investigated Tourmaline Endmembers
O1
Calculating tourmaline compositions from Raman Spectra
O1-H1 Band Assignments
3579 3558 3520
2Å
V =1569.5 Å3
3
7.234 Å
15.92
1Å
1.18Å
Can synthetic tourmalines with restricted compositions facilitate band assignments of Raman spectra?
O4
Maruyamaite (EB13)
7.177 Å
15.89
1Å
V =1558.4 Å
What are the effects of the size of the X-site-occupying ion on tourmaline’s long- and short-range crystal structure?
O4
15.90
2Å 3
Questions: O5
7.178 Å
15.89
c
Tourmaline structure (and crystal) viewed parallel to the c axis.
O3
Dravite (EB28)
V(O3) c
W = O1 = (OH)-, O2-, F-
O3
Dravite (EB29)
a
V = O3 = (OH) , O
H3
Magnesio-foitite (MF2)
a
3+
-
OH-stretching region
Expansion of tourmaline’s unit cell
T = Si , Al , B
O3
O5 O4
3+
Z = Al3+, Cr3+, V3+, Fe3+, Mg2+
Y
O3
3+
[6] [4]
Z
2+
Raman Spectroscopy: OH-stretching region & Short-range effect of X site
-1
, Na+, Ca2+, K+
[6]
O1
c
Single crystal & powder X-ray diffraction: Long-range effect of X site & Al-Mg disorder between Y and Z sites
References: Berryman EJ, Wunder B, Wirth R, Rhede D, Schettler G, Franz G, Heinrich W (2015) An experimental study on K and Na incorporation in dravitic tourmaline and insight into the origin of diamondiferous tourmaline from the Kokchetav Massif, Kazakhstan. Contrib Mineral Petrol, 169:28. Bloodaxe ES, Hughes JM, Dyar MD, Grew ES, Guidotti CV (1999) Linking structure and chemistry in the Schorl-Dravite series. Am Miner, 84: 922-928. Pertlik F, Ertl A, Körner W, Brandstätter F, Schuster R (2003) Na-rich dravite in the marbles from Friesach, Carinthia, Austria: Chemistry and crystal structure. N Jb Miner Mh, 6: 277-288. von Goerne G, Franz G, Wirth R (1999) Hydrothermal synthesis of large dravite crystals by the chamber method. European Journal of Mineralogy 11:1061-1077.
