Ruby and sapphire from the tan Huong-Truc Lau area, Yen Bai province, Northernvietnam

Abstract

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. © 2011 Gemological Institute of America.