Neo-Science of Natural History : Integration of Geoscience and Biodiversity Studies;Proceedings


Study of Macroscopic and Microscopic Reaction Textures Associated with Corundum of Balangoda Region, Sri Lanka

Francis, Muttarachchige D.P.L.;Matsueda, Hiroharu

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KEYWORDS : Reaction textures;Corundum;Calc-silicate;Granulite;Mineralization


Corundum is the most sought after gem variety among Sri Lankan gem minerals. Locations of most of the gem quality stones were identified as alluvial. The in-situ corundums rarely show a gem quality and are mostly associated with macroscopic and microscopic reaction textures. Studies of these textures, associated reactants and the intrusion of corundum by reaction products using electron probe microanalysis and energy dispersive x-ray analysis reveal that hydrous minerals such as phlogopite mica play an important role in promoting such reactions. Because of these reactions corundum is likely to be fractured and the fractures are often filled with reaction products. Hence the gem quality is not retained in most corundum after their formation. Also the natural shielding effect, called plagioclase shielding that protects corundum against the retrograde reactions, is found to be responsible for the production of valuable gem quality stones.