Gemological characteristics and the quality of sapphire from Krong H’Nang - Dak Lak

Sapphires in Krong H'Nang area have been found mainly in deluvialor alluvial placers which related to Pliocene-lower Pleistocene basaltoid formations (βN2-Q1). Their main colors are dark green, yellow-green, yellow more rarely dark blue, yellow-blue-green. Sapphires in this area are transparency, translucency and opaqueness, most of them are opaque. The crystals are from 2–7 mm and sometimes their size can be up to 30–4 0mm. Besides the color zoning reduces color quality in dark blue sapphire, there are also many plagioclase or zircon, fingerprint and liquid-filled inclusions which reduce the clarity of the sapphires. Transparent sapphires with green, yellow-green, yellow are evaluated to be good quality and can be used in jewelry. For translucent and opaque sapphires with dark green, dark blue and transparent sapphires with color zoning, they can be used in jewelry but are not estimated well. Therefore, in order to improve the quality of the latter group, suitable methods such as heat treatment, beryllium diffusion and glass filling are needed.