Characterisation of Eluvial Corundum (Ruby) from Kermunda, Kalahandi District, Odisha, India

Abstract

Corundum and ruby occur sporadically in the soil horizons around Kermunda area, which is situated in Kalahandi district of Odisha. The area is constitutes a part of the Precambrian khondalite-charnockite-granite gneiss terrane of Eastern Ghats. Corundum is light pink while ruby is rose red, carmine or purple red in colour. The corundum and ruby grains contain inclusions of rutile and zircon and are often surrounded by dark coloured spinel exhibiting corona texture. Sapphirine occurs as rim around spinel as well as corundum. Veinlets of hematite and diaspore traverse spinel and sapphirine aggregates. SEM-EDS analysis indicated that (i) corundum and ruby grains contains trace amounts of Fe and Cr, (ii) spinel is pleonaste and chromium pleonaste types and (iii) sapphirine is silica- poor and magnesian rich. The corundum-spinel intergrowth showing corona texture suggests that under high P-T gradient in granulite facies metamorphism, corundum reacted with either phlogopite or garnet to form spinel by the reactions: (i) Corundum + Phlogopite= Spinel + K-feldspar + Water or (ii) Corundum+Garnet = Spinel. Sapphirine is possibly a reaction product of (i) Corundum+Spinel+Garnet= Sapphirine or (ii) Spinel+Silica= Sapphirine.