ThuyetNguyen Thi MinhGems & GemologyRuby and Sapphire from the Tan Huong-Truc Lau Area, Yen Bai Province, Northern Vietnam. Nguyen Ngoc Khoi,Chakkaphan Sutthirat,Duong Anh Tuan,Nguyen Van Nam,Nguyen Thi Minh Thuyet,Nguy Tuyet Nhung. Gems and Gemology . 2011...