Baddeleyite containing ordered srilankite (ZrTi2O6) from Eppawala, Sri Lanka

Abstract

Megacrysts of baddeleyite have been found in a (latest Neoproterozoic) carbonatite near Eppawala, Sri Lanka. The material was characterised using a combination of structural, chemical and spectroscopic analysis techniques, revealing notable internal heterogeneity. The baddeleyite contains variable, significant volume fractions affected by secondary alteration. Further detailed studies will be needed before the material can be considered as potential primary reference material in U-Pb and other isotope-analytical studies. Most remarkable, however, is the occurrence of lamellae of ordered ZrTi₂O₆ (orthorhombic space group Pbcn with a = 14.198 ± 0.002 Å, b = 5.326 ± 0.001 Å, c = 5.002 ± 0.001 Å). Single-crystal X-ray diffraction and Raman microspectroscopy results, including a calculated spectrum, are presented for the newly recognised ordered form of ZrTi₂O₆. In this phase, Zr is eight- and Ti is six-coordinated. It seems to be a hitherto unknown polymorph: So far, only disordered ZrTi₂O₆ with both Zr and Ti in octahedral sites was known to occur in nature. Revisiting known srilankite samples appears worthwhile.