Ruby and Sapphire from the Tan Huong-Truc Lau Area, Yen Bai Province, Northern Vietnam

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. For more than 20 years, Vietnam's Yen Bai Province, and the Luc Yen District in particular, have been widely known for producing highquality rubies and sapphires. Subsequent deposits found elsewhere in Vietnam (Long et al., 2004) include Quy Chau-Quy Hop (Nghe An Province), Di Linh (Lam Dong), Dak Ton (Dak Nong), and Ma Lam and Da Ban (Binh Thuan). Still, Yen Bai remains the country's most important source of ruby and sapphire. Much of the production consists of cabochonquality stones from the Tan Huong-Truc Lau area (e.g., figure 1), as described in this article.Vietnamese geologists first discovered gem-quality corundum and spinel at Luc Yen in 1983 (Vinh, 1991). In early 1987, the Geological Survey of Vietnam found abundant gem material in alluvium in Luc Yen's Khoan Thong area. Mining activity soon thrived, with many companies operating in the region (Voi, 1991). Other gem occurrences near Khoan Thong followed, such as Nuoc Ngap, Hin

Gemstones from Vietnam: An Update

“…Rubies from these two Vietnamese sources can be differentiated by their ratios of Cr 2 O 3 /Fe 2 O 3 and Cr 2 O 3 /TiO 3 , both of which are higher in Luc Yen samples (Hauzenberger et al, 2003). A comparative study of the Yen Bai material by one of the authors (Nguyen et al, 2011) indicated lower Cr and higher Fe in ruby from the newer mines. Furthermore, distinctive internal features in ruby and fancy sapphire from the old mines were presented by Kane et al (1991).…”

“…Supplies of facet-grade ruby from Luc Yen (as well as Quy Chau) have become rare, and cabochon-quality ruby and fancy sapphire are more common (figure 3). One interesting feature of ruby and sapphire from the newer mines is that the crystals are very typically surrounded by spinel, which generally follows the morphology of the underlying corundum crystal (see Nguyen et al, 2011). The boundary between the corundum and the spinel is slightly rounded, suggesting disequilibrium between the two (Häger et al, 2010;Hauzenberger et al, 2010).…”

“…Current production from this deposit totals around 10 kg per month, consisting of 20-30% ruby (and some sapphire) and 70-80% spinel. Only 10-15% of the total production is of cabochon quality; the rest is used for carvings or specimens (Nguyen et al, 2011). An 18.8 kg star ruby of good quality, discovered by DOJI in the Tan Huong mine in 2005, is the largest known Vietnamese ruby specimen (see Nguyen et al, 2011).…”

“…The major deposits are located at An Phu, Khoan Thong, Minh Tien, and Truc Lau in Luc Yen, and at Tan Huong in Yen Binh. The newest deposit, found in February 2010, is Lang Chap, notable for its orange-red padparadscha-like stones (Nguyen et al, 2011). Yet the most productive spinel deposit remains the old Cong Troi mine in An Phu, which yields a wide range of colors (Blauwet, 2010).…”

The Annealing of Corundum (Ruby) in Nitrogen (N2) Air

“…Ruby may contain Ti, V, Ga in trace amounts together with Cr, Fe. Sapphire synthesizes chromium red, nickel yellow, chromium + nickel pinkish orange while producing titanium and iron blue surface [7,22,23]. Changes in the valance values of the elements Fe, Mg, Ca, Ni in the case of the pink color of the ruby color after heat treatment in the nitrogen atmosphere, the heat regulation of these elements in the crystal structure and the changes in the oxygen vacancies are influential.…”