Structure refinement of a birefringent Cr-bearing majorite Mg ₃ (Mg (sub 0.34) Si (sub 0.34) Al (sub 0.18) Cr (sub 0.14) ) ₂ Si ₃ O ₁₂

Yamaguchi University, Department of Advanced Materials Science and Engineering, Yamaguchi, Japan

A single crystal of a birefringent Cr-bearing majorite, Mg ₃ (Mg (sub 0.34) Si (sub 0.34) Al (sub 0.18) Cr (sub 0.14) ) ₂ Si ₃ O ₁₂ , was synthesized at 20 GPa and 2000 degrees C using "6-8" type uniaxial split-sphere apparatus. This garnet is tetragonal with the unit-cell parameters a nearly equal c and deviates slightly from cubic symmetry. The structure refinements using single-crystal X-ray diffraction intensity data were carried out by assuming three space groups (one cubic and two tetragonal) to determine the most probable symmetry. The most probable space group is I4 ₁ /a (tetragonal). The Cr ions show a disordered distribution between the two nonequivalent octahedral sites in the I4 ₁ /a structure.

This record provided courtesy of AGI/GeoRef.

This article has been cited by other articles:

				S. Heinemann and R. Miletich Structure and twinning of tetragonal Ca3Mn2Ge3O12 garnet American Mineralogist, July 1, 2000; 85(7-8): 993 - 1000. [Abstract] [Full Text] [PDF]