TY - JOUR
T1 - Compressibility of synthetic Mg-Al tourmalines to 60 GPa
AU - Berryman, Eleanor J.
AU - Zhang, Dongzhou
AU - Wunder, Bernd
AU - Duffy, Thomas S.
N1 - Funding Information:
Financial support was provided by NSF and NNSA through a subcontract with Washington State University (DE-NA0002007). GeoSoilEnviroCARS is supported by NSF (EAR-1634415) and DOE (DE-FG02-94ER14466). Use of the COMPRES-GSECARS gas-loading system was supported by COMPRES and GSECARS. This research used resources of the Advanced Photon Source, a DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.
Publisher Copyright:
© 2019 Walter de Gruyter GmbH, Berlin/Boston 2019.
PY - 2019/7/1
Y1 - 2019/7/1
N2 - High-pressure single-crystal X-ray diffraction patterns on five synthetic Mg-Al tourmalines with near end-member compositions [dravite NaMg3Al6Si6O18(BO3)3(OH)3OH, K-dravite KMg3Al6Si6O18(BO3)3(OH)3OH, magnesio-foitite ?(Mg2Al)Al6Si6O18(BO3)3(OH)3OH, oxy-uvite CaMg3Al6Si6O18(BO3)3(OH)3O, and olenite NaAl3Al6Si6O18(BO3)3O3OH, where o represents an X-site vacancy] were collected to 60 GPa at 300 K using a diamond-anvil cell and synchrotron radiation. No phase transitions were observed for any of the investigated compositions. The refined unit-cell parameters were used to constrain third-order Birch-Murnaghan pressure-volume equation of states with the following isothermal bulk moduli (K0 in GPa) and corresponding pressure derivatives (K0 = ∂ K0/∂ P)T: dravite K0 = 97(6), K0 = 5.0(5); K-dravite K0 = 109(4), K0 = 4.3(2); oxy-uvite K0 = 110(2), K0 = 4.1(1); magnesio-foitite K0 = 116(2), K0 = 3.5(1); olenite K0 = 116(6), K0 = 4.7(4). Each tourmaline exhibits highly anisotropic behavior under compression, with the c axis 2.8-3.6 times more compressible than the a axis at ambient conditions. This anisotropy decreases strongly with increasing pressure and the c axis is only ~14% more compressible than the a axis near 60 GPa. The octahedral Y- and Z-sites' composition exerts a primary control on tourmaline's compressibility, whereby Al content is correlated with a decrease in the c-axis compressibility and a corresponding increase in K0 and K. Contrary to expectations, the identity of the X-site-occupying ion (Na, 0 K, or Ca) does not have a demonstrable effect on tourmaline's compression curve. The presence of a fully vacant X site in magnesio-foitite results in a decrease of K0 relative to the alkali and Ca tourmalines. The decrease in K0 for magnesio-foitite is accounted for by an increase in compressibility along the a axis at high pressure, reflecting increased compression of tourmaline's ring structure in the presence of a vacant X site. This study highlights the utility of synthetic crystals in untangling the effect of composition on tourmaline's compression behavior.
AB - High-pressure single-crystal X-ray diffraction patterns on five synthetic Mg-Al tourmalines with near end-member compositions [dravite NaMg3Al6Si6O18(BO3)3(OH)3OH, K-dravite KMg3Al6Si6O18(BO3)3(OH)3OH, magnesio-foitite ?(Mg2Al)Al6Si6O18(BO3)3(OH)3OH, oxy-uvite CaMg3Al6Si6O18(BO3)3(OH)3O, and olenite NaAl3Al6Si6O18(BO3)3O3OH, where o represents an X-site vacancy] were collected to 60 GPa at 300 K using a diamond-anvil cell and synchrotron radiation. No phase transitions were observed for any of the investigated compositions. The refined unit-cell parameters were used to constrain third-order Birch-Murnaghan pressure-volume equation of states with the following isothermal bulk moduli (K0 in GPa) and corresponding pressure derivatives (K0 = ∂ K0/∂ P)T: dravite K0 = 97(6), K0 = 5.0(5); K-dravite K0 = 109(4), K0 = 4.3(2); oxy-uvite K0 = 110(2), K0 = 4.1(1); magnesio-foitite K0 = 116(2), K0 = 3.5(1); olenite K0 = 116(6), K0 = 4.7(4). Each tourmaline exhibits highly anisotropic behavior under compression, with the c axis 2.8-3.6 times more compressible than the a axis at ambient conditions. This anisotropy decreases strongly with increasing pressure and the c axis is only ~14% more compressible than the a axis near 60 GPa. The octahedral Y- and Z-sites' composition exerts a primary control on tourmaline's compressibility, whereby Al content is correlated with a decrease in the c-axis compressibility and a corresponding increase in K0 and K. Contrary to expectations, the identity of the X-site-occupying ion (Na, 0 K, or Ca) does not have a demonstrable effect on tourmaline's compression curve. The presence of a fully vacant X site in magnesio-foitite results in a decrease of K0 relative to the alkali and Ca tourmalines. The decrease in K0 for magnesio-foitite is accounted for by an increase in compressibility along the a axis at high pressure, reflecting increased compression of tourmaline's ring structure in the presence of a vacant X site. This study highlights the utility of synthetic crystals in untangling the effect of composition on tourmaline's compression behavior.
KW - Tourmaline
KW - diamond-anvil cell
KW - equation of state
KW - single-crystal X-ray diffraction
KW - synthetic
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U2 - 10.2138/am-2019-6967
DO - 10.2138/am-2019-6967
M3 - Article
AN - SCOPUS:85068329937
SN - 0003-004X
VL - 104
SP - 1005
EP - 1015
JO - American Mineralogist
JF - American Mineralogist
IS - 7
ER -