• journal_title：American Mineralogist
• Contributor：Akihiko Nakatsuka ; Akira Yoshiasa ; Takamitsu Yamanaka ; Eiji Ito
• Publisher：Mineralogical Society of America
• Date：1999-
• Format：text/html
• Language：en
• journal_abbrev：American Mineralogist
• issn：0003-004X
• volume：84
• issue：1-2
• firstpage：199
• section：Articles

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.