• journal_title：American Mineralogist
• Contributor：Simona Quartieri ; Roberta Oberti ; Massimo Boiocchi ; Maria Chiara Dalconi ; Federico Boscherini ; Olga Safonova ; Alan B. Woodland
• Publisher：Mineralogical Society of America
• Date：2006-
• Format：text/html
• Language：en
• Identifier：10.2138/am.2006.2038
• journal_abbrev：American Mineralogist
• issn：0003-004X
• volume：91
• issue：8-9
• firstpage：1240
• section：Articles

Investigation of scandium incorporation in garnets along the synthetic Ca₃Fe³⁺₂ Si₃O₁₂–Ca₃Sc₂Si₃O₁₂ (adr–CaSc) join, based on the same multi-technique approach used in the companion paper (Oberti et al. 2006a), shows that (1) Sc is incorporated exclusively at the Y octahedron; (2) the local coordination of Sc is slightly different in Sc-poor than in Sc-rich compositions (Sc-O = 2.06 Å in CaSc₁₀ vs. 2.10 Å in CaSc_30–90); (3) the local coordination of Ca is also slightly different in Sc-poor than in Sc-rich compositions [Ca1,2-O are 2.34(2) and 2.48(2) Å in CaSc₁₀ and 2.36(2) and 2.50(2) Å in CaSc₉₀, with Δ fixed at 0.14 Å in all the samples]; (4) the linear increase of the unit-cell edge along the join derives from multiple changes in the geometry of the different polyhedra and from the rotation of the tetrahedron around the 4̅ axis (α rotation), and cannot be modeled from extrapolation of the behavior observed along the Ca₃Al₂Si₃O₁₂–Ca₃Fe³⁺₂ Si₃O₁₂ (grs–adr) join.

CaSc-rich garnets, where a large X dodecahedron coexists with a large Y octahedron and a Z tetrahedron occupied by Si, similar to pyrope-grossular garnets, have the highest α values observed to date in calcium silicate garnets. Slightly lower α values are observed in pyrope and almandine, but correspond to a different structural arrangement, where a small X dodecahedron coexists with a small Y octahedron. These results further confirm the efficiency of a combined short- and long-range approach for understanding the properties of garnet solid solutions.