Zirconolites from Sri Lanka, South Africa and Brazil

Abstract

Zirconolites, CaZrTi₂O₇, from Sri Lanka and Pala Bora, South Africa, and a calzirtite, CaZr₃TiO₉, from Jacupiranga, Brazil, were examined using the electron microprobe, x-ray diffraction (annealing study), transmission electron microscopy, scanning electron microscopy and optical microscopy. The x-ray data indicate that all three zirconolites are metamict. Both Sri Lanka zirconolites are amorphous to the limits of resolution of the electron microscope (∼10 A). The Pala Bora zirconolite is largely amorphous but contains isolated domains (50–200 A) of crystalline material which may be the result of post-metamict recrystallization and alteration. The only other significant evidence for chemical alteration was the lower Th concentration (1–2 weight percent) and slightly lower analytic totals for the rims of the Sri Lanka zirconolites. Upon annealing at 1130°C for 5 hours, all three zirconolites recrystallized as microcrystalline aggregates. Refined unit cell parameters and volumes are consistent with published data for synthetic zirconolites. Both Sri Lanka zirconolites contain microvoids, spherical in shape, and 200 Angstroms to 2 microns in size. This porosity may be the result of helium accumulation arising from the decay of U and Th. The calzirtite was highly crystalline, exhibited no porosity, and was unchanged by the annealing treatment.