A series of wadeite solid solutions (Wdss) along the join K2ZrSi3O9 (Zr–wadeite, Zr–Wd)–K2TiSi3O9 (Ti–wadeite, Ti–Wd) was synthesized at 2 GPa and 1,200–1,400 °C for 24 h with a piston-cylinder apparatus. The chemical composition data demonstrated that Ti and Zr readily substitute for each other, and a full series of Wdss exists between the Zr–Wd and Ti–Wd end-members at the P–T conditions of our
... [Show full abstract] synthesizing experiments. The volume–composition relationship at ambient P–T conditions did not show any significant deviation from the Vegard’s law, indicating a nearly ideal mixing between the Zr–Wd and Ti–Wd. All the Raman peaks observed at ambient P–T conditions were linearly correlated with the composition, suggesting an almost full structural relaxation for the Wdss. These findings suggest that the complete mixing behavior along the join K2ZrSi3O9–K2TiSi3O9, as demonstrated by our high-P experiments, may extend to a much wider range of P–T conditions. Consequently, the coexistence of the Zr–Wd and Ti–Wd in the lamproites from the Leucite Hills, Wyoming, may be due to a chemical composition change of the magma rather than a crystal structural limit.
