Characterization of zircons in Buttaia - Okkampitiya gem fields,Sri Lanka: An implication for heat treatment

Abstract

Zircon is considered as a low quality gemstone, with various colour varieties, which is used to traditional heat treatment by Buttala - Okkampitiya gem traders for enhancing its quality and colour. Yellow and pastal green varieties are commonly found in the study area. The green varieties are different from Ratnapura green zircons and the yellow zircons found from the study area are with high radioactivity and consists inclusions that are unique to green zircons. The characteristics such as specific gravity, radioactivity, reflectivity, surface and internal features of zircon samples from heavy mineral concentrates were studied using hydrostatic balance, geiger muller counter, reflectometer, microscope and Visible light spectroscope, UV-VIS-NIR, FTIR and EDXRF techniques. Samples were heat-treated using electric furnace. Heat treatment resulted the yellow and violet zircons to transform into colourless under 800 °C for 2 hrs in oxidation condition, which can be used as a substitute for diamond by their adamantine luster. Under less oxygen condition green zircons become bluish colour. According to the results, yellow zircons show metamict characteristics. The different Zr/Hf ratios from EDXRF indicating the zircons are from different origins. These results can be used as a base for comparison of other gem varieties and as a base for cost effective zircon enhancement.