Spring 2015 G&G Examines Blue Spinel, Chinese Jewellery Design and the Latest in Synthetics
June 12, 2015
Blue spinel is rare in nature and not well-known in world gem markets, but its colour rivals that of sapphire. Luc Yen, located about 100 miles from Hanoi, has been a source of gem-quality ruby, sapphire and red spinel for the past 25 years. Blue spinel is a more recent discovery, not mined in significant quantities until a decade ago. The gems come from three deposits and are hard-won, requiring a four-hour hike, rising 1,800 feet through dense foliage to reach the mine sites.
In primary deposits, the blue spinel crystals are found in a marble layer some 1,500-feet thick. Miners – primarily local farmers working part time – extract it using hand tools and pneumatic drills. However, most of the blue spinels, along with their red counterparts, are found in secondary deposits, where they eroded out of their host rocks and washed into the valleys. Here, the miners use a water hose and sluice to sort out the gem-bearing gravels, which can also include ruby and sapphire.
The authors (Boris Chauvire, Benjamin Rondeau, Emmanuel Fritsch, Phillipe Ressigeac and Jean Lu-Luc Devidal) conducted extensive gemmological analyses of the samples they purchased from local merchants. The colours and saturation varied from deposit to deposit, but ranged from violet-blue to blue and slightly greyish to vivid saturation, and very light to medium-dark tones. Analysis found the most vibrant blue colours came from trace amounts of cobalt, which is similar to blue spinel from some other locations. In addition, the authors present a lot of information on the geology, along with a hypothesis on the gems’ geological origin.
The Chinese Soul in Contemporary Jewellery Design
Historically, Chinese culture - and jewellery design/tastes - was known for its dragon, bamboo and phoenix motifs, as well as its symbolic writing. Today, China is the world’s second largest jewellery market with a growing penchant for brand names and luxury. GIA staff authors, Andrew Lucas, Merilee Chapin, Moqing Lin and Xiaodan Jia profile six designers whose work incorporates traditional motifs and materials with modern sensibilities, combined with traditional Chinese and Western techniques.
- Hong Kong designer Dickson Yewn incorporates traditional door lock motifs and lattice windows in his emerald pieces. The lock motif in the bracelet is meant to symbolise health and happiness for the wearer. The window lattice ring design was patterned after the Classical Gardens of Suzhou, and was worn by Michelle Obama at a banquet honouring Queen Elizabeth II.
- Master Jingyi Bai, who learned her craft from master goldsmiths, creates traditional filigree and inlay art objects. She also creates replicas of historic pieces in the style of the old masters.
- Taiwanese designer Yue-Yo Wang incorporates the ancient art of knotting into modern-styled pieces that feature coloured gemstones such as rose quartz, chalcedony, tourmaline and, of course, jadeite. Jadeite is one of the strongest traditions in Chinese jewel craft and Shanghai designer Kaka Zhang creates jadeite pieces of traditional fairytale characters that she markets mainly online.
- Shirley Zhang, working from Shenzhen, creates highly intricate pieces that combine ancient motifs and innovative techniques, such as gem setting that enables more light to pass through the stones.One of her award winning pieces, “Dancing on Flowers”, features 1,002 coloured stones and 4,986 small diamonds in a suite of three pieces featuring blossoms and bees to symbolise diligence and beauty.
- Jin Ren, of Beijing, bases some of his designs on mythological characters such as the Monkey King. He has created a suite of jewels with colourless, yellow and black diamonds arranged in a snakeskin motif to symbolise renewal, as when a snake sheds his skin.
Amethyst from Boudi, Morocco
Amethyst is one of the most popular gemstones in world markets, and authors Fabrizio Troilo, Abdelghani El Harfi, Salahaddine Mouaddib, Erica Bittarello and Emanuele Costa, from the Instituto Gemmologico Italiano and universities in Italy and Morocco, examined material from the Boudi area of Morocco that is being commercially mined.
While much of the Boudi production has colour and properties similar to amethyst found in other parts of the world, it does produce some fine reddish-purple gems that resemble the top-quality stones produced from classic deposits.
Visible Absorption Spectra of Coloured Diamonds
GIA researchers Dr James Shigley and Dr Christopher Breeding present a review of the absorption features of yellow, pink to red, grey to blue and orange to brown diamonds.
Colourless diamonds have few or no trace elements or growth defects (such as misaligned crystal structure) to absorb certain colours of the spectrum from the light that passes through them, so the light returned is “white”. Elements such as nitrogen and boron, however, absorb certain colours of the spectrum, so the light returned is yellow or blue. Other factors can also cause diamond colour. Natural or artificial radiation displaces some of the carbons atoms from the crystal structure of the diamond to create vacancies that cause a green colour.
The authors have created a colour chart that shows visible absorption spectra for a range of coloured diamonds to serve as a reference tool for researchers and gemmologists.
Mozambique: A Ruby Discovery for the 21st Century
The final full article is from a G&G staff field trip to the Montepuez ruby deposit in Mozambique. The article details the geology of the area that has produced the largest ruby find in recent history and how the rough gems are mined, sorted and graded for sale. The authors, Merilee Chapin, Vincent Pardieu and Andrew Lucas, detail the nature of the rubies in comparison with those from other sources.
This issue features an entry on techniques for identifying very small synthetic diamonds using a microscope equipped with a Fourier-transform infrared (FTIR) spectrometer. The report notes that GIA has seen a surge in faceted melee goods submitted for identification. Combining the FTIR spectrometer with the microscope has enabled GIA researchers to get accurate spectra readings for diamonds as small as .00054 carats. It had been difficult to retrieve proper spectra for diamonds under .01 carat (ct.) before this, because readings were often indistinct and had to be taken while the diamond was in a set position. This set-up allows clear readings to be taken independently of a diamond’s position, whether mounted in jewellery or loose.
The above method was also used to examine a pendant holding 118 diamonds, including 58 fancy yellows and 60 colourless stones. GIA staff found one HPHT-grown synthetic weighing .00431 ct. Nearly all of the other diamonds were natural type 1aA or type 1aAB.
In Hong Kong, GIA recently examined two large synthetic colourless diamonds, submitted with full disclosure by a Russian producer. One was a 4.30 ct. D SI1; the other a 5.11 ct. K I1. Both were HPHT grown and contained distinctive metallic inclusions. The quality and size of these diamonds demonstrates that HPHT synthetic technology has made great strides in recent years.
GIA staff in New York examined two chameleon diamonds, a 0.35 ct. Fancy Deep yellow-green and a 0.27 ct. Fancy Deep greyish yellowish green, both marquise cuts. Spectral analysis revealed that these diamonds were irradiated to enhance their body colour – a process not usually performed on chameleon stones.
Additional GIA lab notes include an analysis of a large (13.69 mm x 11.80 mm) fine colour Quahog pearl with very good symmetry and shape; a report on large specimens of pink and reddish purple cobaltocalcite; a diamond that contains a tiny diamond inclusion that formed in a different geological environment; and conservation concerns over the use of natural large saltwater clam shell (Tridacna) beads in imitation pearls as all species in this family of molluscs are listed in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).
About the Author
Russell Shor is senior industry analyst at GIA in Carlsbad.
Gems & Gemology is GIA’s quarterly technical journal, reporting the latest advances in gemmological research since 1934. G&G Brief presents an overview of the content of the latest issue of the journal.