Abstract

Gem spinels were first discovered in Lục Yên (Yên Bái Province) in 1985, together with ruby and sapphire in placers. Spinels from Lục Yên can be seen in different colors: red, pink, purple, sea blue and sky blue. Gem quality spinels have been found and exploited in placers, meanwhile spinels in host rocks (white marble) are usually of low quality and are used mainly as sample collections. The color of Lục Yên spinel changes depending on the concentration of impurity elements. The presence of chromium (Cr₂O₃) gives red and pink color, the combination of Cr₂O₃ and FeO gives purple color. Cobalt (CoO) gives blue color. Iron ( Fe₂O₃) causes brown shade and brownish luster... An inclusion assemblage has been discovered, consisting of apatite, goethite, rutile, orthoclase and negative crystals.