Aquamarine from the Thuong Xuan District, Thanh Hoa Province, Vietnam

Abstract

dealers, ~100-150 kg of gem material were recovered by local people annually during the past decade, and in 2010 some 300-400 kg were produced. A limited number of gemstones have been faceted so far (e.g., figure 1), and sold mainly into the Vietnamese market. This article describes the geologic setting, gemological properties, and spectroscopic characteristics of Thuong Xuan aquamarine. LOCATION, GEOLOGY, AND MININGThe Thuong Xuan aquamarine deposits lie ~70 km west of the provincial capital, Thanh Hoa City (figure 2). While Thuong Xuan is the only commercially significant aquamarine locality in the country, the adjacent Que Phong District in Nghe An Province has produced small amounts of aquamarine from eluvial deposits.The Thuong Xuan region is cross-cut by a group of mainly northwest-trending faults. The aquamarine is hosted by pegmatites distributed mostly within the Ban Chieng and Ban Muong granite complexes, which together cover an area of 100 km 2 (figure 3). The pegmatite bodies typically form lenses or veins, ranging from 10 to 30 cm thick and a few meters in length to 4-5 m thick and tens of meters long. According to unpublished research by one of the authors (NNK), the pegmatites consist of quartz (38-48%), K-feldspar (~35%), plagioclase (18-24%), muscovite (2.3-3.5%), and biotite (0-2%). Quartz, feldspar, aquamarine, topaz, tourmaline, fluorite, and (rarely) zircon are found in miarolitic cavities. Although the topaz is of gem quality, it is not hosted by the same pegmatites as the aquamarine.Many eluvial occurrences of aquamarine are known, of which four-Ban Pang,

Color Characteristics of Blue to Yellow Beryl from Multiple Origins

“…This was in agreement with the fact that Na + coordinates with type II water molecules in the channel (see figure 11A) and each alkali was nearly proportional. Beryl samples from most localities were in the low-alkali beryl area including Pakistan, Russia, Africa, Mozambique, Italy (Bocchio et al, 2009), Vietnam (Huong et al, 2011), Thuong Xuan, Vietnam (Huong et al, 2011) Minas Gerais, Brazil (Viana et al, 2002) Masino-Bregaglia Massif, Italy (Bocchio et al, 2009) and Minas Gerais, Brazil (Viana et al, 2002). Although this Li-Cs plot could not be used to distinguish the exact geographic origin, it showed the possibility of separating blue to yellow beryl from locations worldwide by various chemical fingerprint diagrams.…”

A Study on Beryl in the Cuonadong Be-W-Sn Polymetallic Deposit, Longzi County, Tibet, China

“…(b) Al versus the sum of its substituents in Y site, in atoms per formula unit (apfu). Other sources are [3,18,19,21,22,48,49].…”

“…The K 2 O content is between 0.01 and 0.45 wt%. The Cs 2 O content is between 0.161 and 0.247 wt%, and the ratio of Na [18,[20][21][22]55].…”

“…As observed in Figure 13, aquamarine in most areas belongs to the "low-alkali beryl" area, including Longzi aquamarine. [18,[20][21][22]55].…”

Gemstones from Vietnam: An Update

“…(Obtained from a color-zoned sample; Laurs et al, 2002) Pink: 0.018 (Laurs et al, 2002) Healed fractures, color zoning, unknown solid inclusions (Laurs et al, 2002) medium blue with moderate saturation. While no internal features are considered locality specific, chemical data of samples from Thuong Xuan have identified low amounts of K and Na and high amounts of Fe and Cs compared to other sources (Le et al, 2011). Although emerald and more recently heliodor finds have been reported in nearby Chinese and Cambodian localities (Laurs, 2010), they have not yet been uncovered in Vietnam.…”