Browsing by Author "Illangasinghe, I.K.M.S.C.K."

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Investigation of Geuda Gemstones, before and after the Heat Treatment using FTIR Spectroscopy
    (Uva Wellassa University of Sri Lanka, 2020) Ramesh, T.G.; Jaliya, R.G.C.; Illangasinghe, I.K.M.S.C.K.; Diyabalanage, S.; Jayasinghe, N.; Dharmaratne, T.S.
    Geuda is a low-quality form of corundum and abundant in the most gem enriched regions in Sri Lanka and can transfer into premium blue sapphires, similar to the natural in appearance through heat treatments. The study intended to identify characteristic features to distinguish heated geuda from natural sapphire using FTIR Spectroscopy. 53 geuda samples were collected from five gem bearing localities Ratnapura, Ridiyagama, Okkampitiya, Bakamuna, and Katharagama and heat treated up to 1800°C for the onehour soaking period under reducing environmental condition. Study samples were subjected to FTIR analysis before and after the heat treatment and could identify the development of a distinctive peak at 3310 cm-1 after treatment. This is due to the diffusion of atmospheric Hydrogen back into the crystal and appears in the absorption spectrum as an interstitial O-H bond in the corundum crystal structure. Further, two absorption bands at 2342 or 2362 cm-1 which corresponds to atmospheric CO2 and CO2 gas in negative crystals were observant in almost of the samples and as a direct response to CO2 gas in negative crystals, the intensity of this particular peak is found to be significantly less for Ridiyagama samples with respect to other localities. This reveals that the Ridiyagama samples are with less CO2 trapped inclusions. Nevertheless, certain 2853 and 2924 cm-1 peaks were observed before and after heat treated stones due to the C-H bond resulted in contamination. Furthermore, 3620 and 3697 cm-1 absorption bands related to Kaolinite hydrous mineral inclusions have been disappeared with heat treatment. This concludes to identify heat treated sapphires with 3310 cm-1 peaks and remaining of 3620 and 3697 cm-1 peaks verify it as a non-heat-treated sapphire. Hence, the FTIR technique could be clarified as one of the best methods to identify heat treated blue sapphires. Keywords: Heat treatment, FTIR analysis, Negative crystals, Absorption spectrum, Inclusions
  • No Thumbnail Available
    Item
    Investigation of the Origin of Radioactive Mineral in Godakawela Gem Field, Rathnapura in Sri Lanka
    (Uva Wellassa University of Sri Lanka, 2020) Kuruppu, K.A.D.D.N.; Hewathilake, H.P.T.S.; Illangasinghe, I.K.M.S.C.K.; Ranasinghe, R.A.N.C.; Jayasinghe, N.; Dharmaratne, T. S.
    Sri Lanka is well known for high-quality gemstones and 25% of the total land area is liable for potential gem fields. However, the identification of new gem bearing areas in Sri Lanka is mostly conducted by the sedimentological and geochemical analysis. Notably, most of the gem bearing areas have been associated with radioactive minerals (RAMs). Hence, the in-situ radioactivity survey is an important tool that has not been carried out intensively in Sri Lanka. Recent studies have revealed that the Godakawela gem field (GGF) in Rathnapura has an interesting radioactiveness. Therefore, the present study has conducted to investigate the type of the origin of the RAMs in GGF. The ambient gamma dose rate was measured by the plastic scintillation detector from 40 points in random walk mode and gamma energy was recorded in the NaI scintillation detector. Further, field observations, associated minerals, and surrounding geology were also considered together with the anomaly results. Anomaly results have proved that the GGF has high radioactiveness of 1305 nSv h-1 gamma radiation, which is ten times greater than the average baseline value in Sri Lanka. Peak anomaly observed in the base of the valley has shown a decrement in gamma dosage of 476 nSv h-1 compared to the mid-region of the slope. Hence, if it is a secondary deposit, a considerable amount of the RAMs must be settled to the low altitude area of the valley and given high peak anomaly. Godakawela is located in the Highland-Vijayan boundary which is also known to be fluoride-rich, and well-formed crystals of tourmaline have been associated in the area. Similarly, a large pegmatitic origin of the vein quartz deposit has been identified in this region. Therefore, depending on the distribution of radioactive anomaly patterns and the presence of associated minerals such as well-formed crystals of zircon, tourmaline together with the surrounded geological aspects has identified that the RAMs have primary origin in GGF. Keywords: Radioactiveness, Radioactivity survey, Gamma dose, Primary origin