Primary and secondary deposits in the Tan Huong–Truc Lau area of northern Vietnam’s Yen Bai
Province have supplied rubies (especially star rubies) and some sapphires—mostly of cabochon
quality—for more than a decade. The gems are typically translucent to semitransparent and pink
to purplish or brownish red, with rare color zoning. The most distinctive features of this corundum
after polishing include growth zoning and asterism. The samples contain relatively high
amounts of Fe and variable Ti and Cr. The geologic origin and gemological properties of this
corundum are distinct from that of the adjacent Khoan Thong–An Phu area.