Mineralogical characteristics and the gem quality of corundum in Khe tre area, Eakar, Daklak

Ngoc Kim Bui, Hoang Kim Nguyen

Corundum in Khe Tre area essentially distributes in pegmatite bodies that intruded the granite of Ea Dui complex ((P-Ted) and metamorphic rocks of Ea Rock formation (PR2er). Corundum mainly developed within pegmatite bodies and in contact metasomatic endozone between pegmatite and granite or gneiss. Mineralogical composition of pegmatite is as follows; Major minerals: alkali feldspar (orthoclas, microlin) 60 -70 %, quartz ~ 15 %; Minor minerals: plagioclase, biotite, muscovite Accessory minerals: garnet, zircon, sphene, apatite,…The corundum here was found in intergrowth with feldspar and characterized by dark to dark blue (very rare) hue, opaque diaphaneity, subhedral to anheral crystals and few mineral inclusions. The size of corundum crystals varies from about 2 cm to 5 cm. Rough corundum crystals are rarely of gem value. Most of them can be used only as abrasibve material. For improvement of corundum to be used as gemstones, heat treatment method was proposed.

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