US EPA

6878465 

Journal Article 

Single-crystal X-ray diffraction of grunerite up to 25.6GPa: a new high-pressure clinoamphibole polymorph 

Yong, T; Dera, P; Zhang, D; , 

2019 

1 

Physics and Chemistry of Minerals
ISSN: 0342-1791 

SPRINGER 

NEW YORK 

46 

3 

215-227 

English 

10.1007/s00269-018-0999-1 

WOS:000463607600002 

http://link.springer.com/10.1007/s00269-018-0999-1
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High-pressure single-crystal X-ray diffraction experiments were conducted on natural grunerite crystals with composition (Fe5.237Mg1.646Ca0.061Mn0.051Na0.015Ti0.002Cr0.001K0.001)(Si7.932Al0.083)O-22(OH)(2,) using a synchrotron X-ray source. Grunerite has C2/m symmetry at ambient conditions. The samples were compressed at 298K in a diamond-anvil cell to a maximum pressure of 25.6(5) GPa. We observe a previously described phase transition from C2/m () to P2(1)/m () to take place at 7.4(1)GPa, as well as a further transition from P2(1)/m () to C2/m () at 19.2(3)GPa. The second-order Birch-Murnaghan equation of state fit to our compressional data, yielded the values V-0=914.7(7)angstrom(3) and K-0=78(1)GPa for -grunerite, V-0=926(5)angstrom(3) and K-0=66(4)GPa for -grunerite and V-0=925(27)angstrom(3) and K-0=66(13)GPa for -grunerite. The - phase transition produces a greater degree of kinking in the double silicate chains of tetrahedra accompanied by a discontinuous change in the a and c unit cell parameters and the monoclinic angle. At 22.8(4)GPa the O5-O6-O5 kinking angle of the new high-pressure C2/m phase is 137.5(4)degrees, which is the lowest reported for any monoclinic amphibole. This study is the first structural report to show the existence of three polymorphs within an amphibole group mineral. The high-pressure -phase illustrates the parallel structural relations and phase transformation behavior of both monoclinic single and double chain silicates. 

Physical Sciences - Other Topics; Amphibole, Phase transition, High pressure, Single-crystal X-ray; diffraction, Diamond anvil cell, Synchrotron source; phase-transition, upper-mantle, high-temperatures, in-situ, amphiboles,; chemistry, stability, compressibility, behavior, system