Revision of Y³⁺ ionic radii in common minerals based on trace element partitioning Available to Purchase

The ionic radii of rare-earth elements (REE: Sc, Y, and the lanthanides) are key to interpreting partitioning behavior between minerals and melts for use as petrogenetic tracers and thermometry. Of REE, Y commonly has the highest concentration, and serves as a reference against which other REE concentrations or partition coefficients can be compared. Here, we show that published experimental data on mineral-melt partitioning of REE imply the ionic radius of Y³⁺ is smaller than commonly assumed by 0.001 Å for 6-fold coordination to 0.005 Å for 8- and 9-fold coordination. This difference reconciles the partitioning behavior of Y³⁺ compared to other REE and improves reference states for interpretations of trace element systematics in rocks. Thermobarometry can be highly sensitive to assumed ionic radii, and downward correction of the radius for Y³⁺ improves some REE-based temperatures by hundreds of degrees. Future studies that employ the most common tabulations of ionic radii of the REE (Shannon, 1976, Acta Crystallographica A, A32, 751-767) should use an ionic radius of Y³⁺ of 0.899, 1.014, and 1.070 Å for 6-, 8-, and 9-fold coordination, respectively; alternatively, the ionic radius of Y can be scaled to that of Ho³⁺ x 0.9984. More generally, trace element partitioning data coupled with theoretical models provide a highly precise method to refine effective relative ionic radii in minerals where direct structural determinations are not possible.