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This fine 161 ct Melo pearl is from Phan Thiet, on the south coast of Vietnam. Photo by Pham Van Long. 

This fine 161 ct Melo pearl is from Phan Thiet, on the south coast of Vietnam. Photo by Pham Van Long. 

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This article describes the major gem materials of Vietnam, together with their new finds and recent production. The gemological properties and chemical composition of ruby, sapphire, spinel, tourmaline, garnet, and peridot from the most important Vietnamese sources are updated. Other gems such as aquamarine, green orthoclase, topaz, zircon, quartz,...

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... pearls are recovered off the coast of Vietnam, Thailand, Myanmar, and Malaysia (Pardieu, 2009). Vietnam is the leading source of these pearls (e.g., figure 21). They are found in Ha Long Bay and along the southern coast from Nha Trang to Phan Thiet. ...

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Citations

... were mainly distributed in the later. The Luc Yen is well known for producing multiple color spinels as well as ruby and sapphire (Pham et al., 2013), as indicated in figure 4. In Luc Yen, red color spinels mainly comes from calcic to dolomitic marble, and some are associated with clinochlore or phlogopite, while other colors come from complex metasomatic marbles which have a similar formation environment as marble hosted rubies (Huong et al., 2012). Our samples in this study were collected from Luc Yen area. ...
Article
Gem-quality pink-red spinels produced in Burma, Tanzania and Vietnam have been investigated for their gemological, spectroscopic and chemical characteristics. Microscopic examination revealed octahedral negative crystals and fingerprint inclusions as well as mineral inclusions, such as silicate and carbonate, to be most frequently observed in Burmese spinels. The presence of dust-like tiny exsolved particles are indicative internal features for spinels from Tanzania. The stellate dislocation needles are typical of spinels from Vietnam. Trace elements and further linear discriminant analysis (LDA) could help further distinguish spinels by a group of trace elements mainly composed by Ti, Fe, Zn, Cr, V, etc.
... The gemological properties (especially the internal features) of spinels have been discussed in many papers (e.g. Gübelin and Koivula, 2008;Malsy and Klemm, 2010;Huong et al., 2012). The most interesting inclusion type in the internal world of spinels are the solid inclusions. ...
... They are combination spectra with variable ratios of the spectral components [Cr 3+ ], [V 3+ ] and [Fe 2+ ]. Detailed studies on the color and absorption behavior of spinels from Burma, Vietnam and Tajikistan were published by Malsy et al. (2012) and Huong et al. (2012). Peretti et al. (2015) distinguish three color groups (purple to green -brown or orange-red -pink to vivid red) to describe and compare Burmese spinels from Mogok and Namya. ...
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... Vietnam is the main producer of gem spinels found in primary (marble type) and secondary (placer) deposits. Spinel is exploited in small-scale mines and the most significant deposits are found in North Vietnam along the Red River Shear Zone (Huong et al., 2012;Pham et al., 2013). Vietnamese spinels have been investigated by different authors in terms of geological setting as for the discovery of the Lang Chap deposit in the Tan Huong-Truc Lau area (Malsy et al., 2012), gemmology , trace elements chemistry (Pham et al., 2004;Malsy&Klemm, 2010;Kleišmantas&Daukšyte, 2016;, 2017;Huong et al., 2018) and genesis (Hauzenberger et al., 2001;Chauviré et al., 2015). ...
Article
Trace elements investigated by electron microprobe analysis (EMPA) have been combined with oxygen isotopic composition of pink, red and other colored spinels (blue, purple, brown, orange, lavender) hosted by marbles and found in placers from Luc Yen and An Phu deposits, Yen Bai province, North Vietnam. The deposits are those from Nuoc Ngap, Cong Troi, Bai Son and different placers from the An Phu area. Trace elements such as Fe-Zn-Cr-V in red and pink gem spinels permit to separate those from Cong Troi and those from the others deposits of the An Phu area. Spinels from Cong Troi have low to extremely low Zn (< 500 ppm) and high Fe contents (3,000 to 16,000 ppm) while those from An Phu area are Zn-rich (up to 11,000 ppm). Iron is the dominant element for the other colored spinels whereas Zn, Cr and V contents are extremely variable. The Bai Son blue spinel is Fe-rich (5,000 to 7,200 ppm) with some V (950 to 1,830 ppm), Cr (270 to 480 ppm), Co (240 to 400 ppm) and Ni (550 to 950 ppm). The O-isotope composition of the whole spinels ranges between 12.1 and 24.2‰ (n = 25). Within each deposit, the range of δ18O values for red, pink and colored spinels is usually similar. However, the red and pink spinels from An Phu present two distinct sets of δ18O values, respectively between 13.2 to 17.0‰ (n = 7) and 22.5< δ18O < 24.2 (n = 5). Those from Cong Troi are from 14.8 to 17.7‰ (n = 3) and their range overlaps that of An Phu. The use of O-isotopes is not useful for distinguishing between the deposits, but the low to extremely low Zn content of the Cong Trois spinels is a discriminant. The variation of δ18O values (12.1 <δ18O < 24.2‰) of the whole spinels indicates that the oxygen isotopic compositions of the metamorphic fluids were probably buffered by the local δ18O values of the impure host marbles.ReferencesChauviré B., Rondeau B., Fritsch E., Ressigeac Ph., Devidal J.-L., 2015. Blue spinel from the Luc Yen district of Vietnam. Gems & Gemology, 51, 2-17.D'Ippolito V., Andreozzi G.B., Hålenius H., Skogby H., Hametner K., Günther D., 2015. Colour mechanisms in spinel: cobalt and iron interplay for the blue colour. Physics and Chemistry of Minerals, 42, 431-439.Garnier V., 2003. Les gisements de rubis associés aux marbres de l’Asie Centrale et du Sud-est: genèse et caractérisation isotopique. PhD thesis INPL, Nancy, France, 373p.Garnier, V., Ohnenstetter, D., Giuliani, G., Maluski, H., Deloule, E., Phan Trong Trinh, Pham Van Long, Hoang Quang Vinh, 2005. Age and significance of ruby-bearing marbles from the Red River shear zone, northern Vietnam. The Canadian Mineralogist, 43, 1315-1329.Garnier V., Giuliani G., Ohnenstetter D., Fallick A.E., Dubessy J., Banks D., Hoang Quang Vinh, Lhomme Th., Maluski H., Pêcher A., Bakhsh K.A., Pham Van Long, Phan Trong Trinh, Schwarz D., 2008. Marble-hosted ruby deposits from central and Southeast Asia: towards a new genetic model. Ore Geology Reviews, 34, 169-191.Giuliani G., Fallick A.E., Garnier V., France-Lanord Ch., Ohnenstetter D., Schwarz D., 2005. Oxygen isotope composition as a tracer for the origins of rubies and sapphires. Geology, 33(4), 249-252.Giuliani G., Fallick A.E., Boyce A.J., Pardieu V., Pham Van Long, 2017. Pink and red spinels in marble: trace elements, oxygen isotopes, and sources. The Canadian Mineralogist, 55, 743-761.Hauzenberger C.A., Häeger T., Baumgartner L.P., Hofmeister W., 2001. High-grade metamorphism and stable isotope geochemistry of N-Vietnamese gem-bearing rocks. In: Proceedings of the Workshop on gems and minerals of Vietnam, Hanoi, 124-138.Hauzenberger C.A., Bagola C., Häeger T., Muellen C., Nguyen Ngoc Khoi, Le Thi Thu Huong, 2014. Mineralogy and petrology of the An Phu marble hosted spinel and corundum deposit, Luc Yen, N-Vietnam. In Proceedings of the 4th International Gem and Jewelry Conference, Chiang Mai, Thailand, 76-78.Kleišmantas A., Daukšyte A., 2016. The influence of Vietnam and Sri Lanka spinel mineral chemical elements on colour. Chemija, 27, 45-51.Kretz R., 1983. Symbols for rock-forming minerals. American Mineralogist 68, 277-279.Le Thi Thu Huong, Häeger T., Hofmeister W., Hauzenberger C., Schwarz D., Pham Van Long, Wehmeister U., Nguyen Ngoc Khoi, Nguy Tuyet Nhung, 2012. Gemstones from Vietnam: An update. Gems & Gemology, 48, 158-176.Le Thi Thu Huong, Tobias Haeger, The-Long Phan, 2018. Study of impurity in blue spinel from the Luc Yen mining area, Yen Bai Province, Vietnam. Vietnam J. Earth Sci., 40(1), 46-54.Malsy A., Klemm L., 2010. Distinction of gem spinels from the Himalayan mountain belt. Chimia, 64(10), 741-746.Malsy A., Karampelas S., Schwarz D., Klemm L., Armbruster T., Tuan Do Anh, 2012. Orangey-red to orangey-pink gem spinels from a new deposit at Lang Chap (Tan Huong - Truc Lau), Vietnam. The Journal of Gemmology, 33, 19-27.Pham Van Long, Hoang Quang Vinh, Garnier V., Giuliani G., Ohnenstetter D., Lhomme,T., Schwarz D., Fallick A.E., Dubessy J., Phan Trong Trinh, 2004. Gem corundum deposits in Vietnam. Journal of Gemmology, 29, 129-147.Pham Van Long, Pardieu V., Giuliani G., Nguy Tuyet Nhung, Pham Thi Thanh Hien, Pham Duc Anh, Nguyen Ngoc Khoi, Hoang Quang Vinh, 2014. Gemmological characteristics of spinel from Luc Yen, Yen Bai. Journal of Geology, 340, 29-36.Pham Van Long, Pardieu V., Giuliani G., 2014. Update on gemstone mining in Luc Yen, Vietnam. Gems & Gemology, 49, 233-245.Pouchou J.L., Pichoir F., 1991. Quantitative analysis of homogeneous or stratified microvolumes applying "PAP" In Electron Probe Quantification (K.F.J. Heinrich & D.E. Newbury eds.). Plenum Press, New York, USA, 31-75.Valley J.W., 1986. Stable isotope geochemistry of metamorphic rocks. Reviews in Mineralogy, 16, 445-481.Yui T.F., Khin Zaw, Wu C.-M., 2008. A preliminary stable isotope study on Mogok ruby, Myanmar. Ore Geology Reviews, 34, 182-199.
... In contrast, enrichment of Fe 3+ presents dark brown, while small amount of Fe 3+ makes the color prone to green or even blue-green 35 when Fe 2+ is oxidized to Fe 3+ . On the other hand, Cr 3+ is the key factor of red appearance, which usually give red or pale pink colors to the spinel 36 . The joint effect of Fe 2+ and Cr 3+ then produce colors in violet-red or dark violet, but the color will tend to orange when Fe 3+ replace part of the Cr 3+ . ...
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In this work, we present laser coloration on 304 stainless steel using nanosecond laser. Surface modifications are tuned by adjusting laser parameters of scanning speed, repetition rate, and pulse width. A comprehensive study of the physical mechanism leading to the appearance is presented. Microscopic patterns are measured and employed as input to simulate light-matter interferences, while chemical states and crystal structures of composites to figure out intrinsic colors. Quantitative analysis clarifies the final colors and RGB values are the combinations of structural colors and intrinsic colors from the oxidized pigments, with the latter dominating. Therefore, the engineering and scientific insights of nanosecond laser coloration highlight large-scale utilization of the present route for colorful and resistant steels.
... Other studies claimed that the yellow colour of heliodor is in fact linked to a substitution of Fe 3+ on a tetrahedral site, that is, Be or Si (Solntsev & Bukin, 1997;Andersson, 2013). For further recent work on natural beryl crystals see Huong et al. (2012) and Fridrichová et al. (2015). ...
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Beryl in different varieties (emerald, aquamarine, heliodor etc.) displays a wide range of colours that have fascinated humans throughout history. Beryl is a hexagonal cyclo-silicate (ring-silicate) with channels going through the crystal along the c-axis. The channels are about 0.5 nm in diameter and can be occupied by water and alkali ions. Pure beryl (Be3 Al2 Si6 O18 ) is colourless (variety goshenite). The characteristic colours are believed to be mainly generated through substitutions with metal atoms in the lattice. Which atoms that are substituted is still debated it has been proposed that metal ions may also be enclosed in the channels and that this can also contribute to the crystal colouring. So far spectroscopy studies have not been able to fully answer this. Here we present the first experiments using atomic resolution scanning transmission electron microscope imaging (STEM) to investigate the channel occupation in beryl. We present images of a natural beryl crystal (variety heliodor) from the Bin Thuan Province in Vietnam. The channel occupation can be visualized. Based on the image contrast in combination with ex situ element analysis we suggest that some or all of the atoms that are visible in the channels are Fe ions.
... , the Vietnamese samples showed gemological properties similar to those noted for peridot from other sources found in xenoliths within basalt (Gübelin, 1981; Koivula, 1981; Stockton and Manson, 1983; Koivula and Fryer, 1986; Fuhrbach, 1992; Kane, 2004; Adamo et al., 2009; Huong et al., 2012). Color. ...
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From 2009 to 2011, sapphire crystals and corundum-bearing rocks were discovered at Sutara, in the Jewish Autonomous Region of the Russian Far East. These sapphires are typically translucent to semitransparent and blue to pinkish blue. Most of the crystals are heavily included and display prominent growth zoning, twinning planes, and abundant exsolution lamellae. Their primary fluid inclusions contain diaspore crystals and a lowdensity CO2-CH4 mixture. These inclusions indicate that sapphire mineralization occurred by means of low-density aqueous-carbonic fluids, which were able to carry significant concentrations of alumina. These fluids may have formed as a result of thermal impact of granitic magma on carbonate country rocks. The authors consider Sutara a metamorphic occurrence that formed as a result of diffusive and metasomatic processes at a region of contact between carbonate rocks and pegmatite veins.
... The Cổng Trời mine in northern Vietnam is a wellknown producer of various colours of spinels that are occasionally associated with orange clinohumite (e.g. Huong et al., 2012). This marble-hosted deposit is located ~3 km from An Phú in the Lục Yên District of Yên Bái Province. ...
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... The geology of northern Vietnam is dominated by metamorphic rocks inherited from these two major orogenic events. The first one, the Indosinian orogeny, led to the collision of the main shields (Yangtze and Indochina) during the Permo-Triassic at about 240–245 Ma (Kušnír, 2000; Lepvrier et al., 2008; Huong et al., 2012). In the later orogeny, the Himalayan collision during the Tertiary period, the terrains were strongly reworked. ...
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The Luc Yen district of northern Vietnam is a very productive gem province and the leading source of vivid blue spinel. This study characterizes the origin and gemological properties of these spinels, especially the cause of their unusually bright color, which is directly related to their value. Chemical and spectroscopic analyses indicated that the blue color is due to cobalt (Co2+), with some iron contribution. Petrographic examination identified the context of the gem's formation, which appears to be linked to intense metamorphism during successive orogenies. The carbonate platforms in the ancient Paleo-Tethys Ocean were sandwiched and highly deformed during this orogeny, leading to marble and spinel formation. The authors propose that the cobalt (and to a lesser extent the iron) necessary for the blue color were transported by fluids during metamorphism of the sedimentary sequence.
... Our samples had the following qualities: (1) aquamarines were prismatic, usually terminated with basal pinacoids and individual crystal length of approximately 1-1.5 cm, clarity was translucent or semi-transparent and the colour was deep blue with a green or yellow tone and (2) yellow beryls were non-prismatic, poorly finished, sharp edged and angular, approximately 1-2 cm in length, with transparent and translucent clarity and coloured deep yellow. Aquamarine is reported to be the only beryl gem variety produced in Vietnam, with some Vietnamese dealers stating that a large volume of pale aquamarine from Vietnam is irradiated in Laos and then sold back on the domestic market as natural heliodor (Huong et al. 2012). ...
... The best colour and clarity for gemmological purposes were achieved in aquamarine heated at 700 °C. If we presume that radiation induced the yellow beryl colouring (Huong et al. 2012), heating at 500 °C most likely resets the artificial yellow to the original very pale blue. ...
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Optical and crystal-chemical changes in two beryl varieties after the heat treatment were determined using a wide spectrum of analytical methods. Studied aquamarines are generally more enriched in Fe (up to 0.25 apfu) and alkali (up to 0.08 apfu) than yellow beryls (up to 0.07 apfu Fe, up to 0.04 apfu alkali). The determined c/a ratio of 0.997-0.998 classified all our studied beryls as “normal” beryls. While no crystal structure changes were observed in samples heated to 700°C, those heated to 900 and 1100°C exhibited cracks and fissures. Reduced Fe occurred in samples heated between 300 and 700°C and subsequent oxidation from 900 to 1100°C induced changes in their colour and clarity. The Fe-bearing beryl colour is controlled by the position of the absorption edge and the presence of a broad band attributed to Fe2+ in the NIR region. Blue colour results from the absorption edge located deeper in the UV region and the presence of broad band in the NIR region. Shift of absorption edge to the visible region at the presence of the broad band gives a yellow colour. Although our studied beryls are enriched in H2O I molecule due to their low alkali content, the H2O II molecule is also present. The following two dehydration processes were observed; (1) release of one double-coordinating H2O II molecule at 300-500°C, and (2) total dehydration at 900-1100°C. The observed cracks and fissures likely resulted from channel water release in large beryl crystals.
... The successive growth zones are red (R, R'), Violet (V, V') and intermediary (I, I') colors which are associated to a coeval variation of chromium (Cr 2 O 3 ) and titanium (TiO 2 ). Garnier 2003, Pham et al. 2004, Nguyen et al. 2011, Le et al. 2012. Galibert & Hughes (1995) reported that ruby-bearing marble was discovered in Yunnan province, China, at the beginning of the 1980s. ...
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Gem deposits are rare because in general the conditions that promote their formation are unusual and thus worthy of scientific study. Recently, modern geological and analytical techniques have been applied to gem occurrences worldwide, and our models and understanding of their formation are being radically altered. This short course volume looks at gemstones from a geological perspective and reviews our current understanding of diamond, ruby, sapphire, and emerald deposits, but will also examine the lesser known coloured gems.