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1 Dipartimento di Scienze della Terra, Università di Messina, Salita Sperone 31, I-98166 Messina S. Agata, Italy
2 CNR, Istituto di Geoscienze e Georisorse, Unità di Pavia, via Ferrata 1, I-27100 Pavia, Italy
3 Centro Grandi Strumenti, Università di Pavia, via Bassi 21, I-27100 Pavia, Italy
4 Dipartimento di Fisica and CNISM, Università di Bologna, Viale Berti Pichat 6/2, I-40127 Bologna, Italy
5 European Synchrotron Radiation Facility, 6 rue Jules Horowitz, BP 220, F-38043 Grenoble Cedex, France
6 Institut für Mineralogie, Universität Frankfurt, Senckenberganlage 30, D-60054 Frankfurt, Germany
Correspondence: * E-mail: simonaq{at}unimo.it
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 CaSc30–90); (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 
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 
axis (
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 values observed to date in calcium silicate garnets. Slightly lower 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.
Key Words: Crystal structure • garnet • XAS • XRD data • trace elements and REE • scandium • crystal synthesis
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