Abstract:
Ruby, Sapphire, and Emerald are the gem varieties that come under the precious gem
category. Therefore, they have a high economic value in the global gem market. Semiprecious
gem types are already gaining significant commercial importance in the worldwide
gem trade. Gem quality Spinels has a high demand as a semi-precious gem variety. Sri Lanka
is very famous for gem-quality Spinels, but apart from that, a high quantity of low gemquality
dark Spinels are found in Sri Lankan gem fields. Currently, the Sri Lankan gem
industry is facing the challenge of enhancing the clarity and transparency of dark spinel
using heat treatment techniques. Therefore, this study focused on whether the Sri Lankan
dark Spinels can be lightened through heat treatment and to develop a heat treatment
technique for clarity enhancement of dark Spinels. Spinel samples were analysed to find the
content of d block transitional elements which are responsible for the formation of colours in
crystals. X-ray fluorescence spectroscopy was used to provide information about the
chemical composition and trace element content of Spinel samples. The samples were heattreated
in oxidising and reducing conditions at a temperature ranging from 600° C to 1800° C
for 1 hour to 6 hours using the Lakmini gas furnace to find the critical temperature at which
Spinels change their current state of transparency. Chemical analysis has proved the dark
Spinels primarily consist of high Fe and Zn content. Some rare elements, such as Pt, are also
found apart from 3d transitional elements. The critical temperature at which Spinels enhance
their clarity was around 1050° C. Prominent clarity enhancement was observed in samples
that contained a high percentage of 3d transitional elements such as Mn, Cr, and Cu. The
results of this research proved that dark spinel could be value-added by heat treatment.
Citation:
Samaranayake, K.P.R.N., Balasooriya, N.W.B., Illangasinghe, S. (2021). Value addition of Sri Lankan dark spinels through a heat treatment technique. In D.M.D.O.K. Dissanayake & C.L. Jayawardena (Eds.), Proceedings of International Symposium on Earth Resources Management & Environment 2021 (p. 127). Department of Earth Resources Engineering, University of Moratuwa. https://uom.lk/sites/default/files/ere/files/ISERME%202021%20Proceedings_2.pdf