Thorium-Rich Zircon From the Idar Pegmatite, Sabarkantha District, Gujarat

Cyrtolite variety of zircon rich in thorium occurs as pockets of radiating, multiple intergrowth crystals in a pegmatite emplaced in the Idar granite, Sabarkantha district, Gujarat. It has a lower specific gravity (3.86-4.4) and micro-Hardness (676-835), compared to crystalline zircon (4.71 and 841-1468) respectively. The mineral analysed lower contents of SiO₂ (23.89%) and ZrO₂ + HfO₂ (43.36%), compared to normal zircon, and high contents of ThO₂ (5.06%), UO₂ (0.74%), Rare Earth Oxides (REO) (7.88%), FeO (4.44%), CaO (1.98%), MnO (1.26%), H₂O (7.95%). Accumulated damage to the crystal structure caused by the presence of appreciable amount of radioelements (5.06% ThO₂ and 0.74% UO₂) and also REO (7.88%) in the phase, aided in its metamictisation, hydration and alteration resulting in cyrtolite formation. On heating at 900±C the re-Crystallised material yielded zircon x-Ray pattern. The "d" spacings, intensities of the reflections obtained and increase in the size of unit cell determined for the specimen, compared to that of standard zircon, matches well with the observations made for similar metamict cyrtolites studied by others.