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Carlsbad, United States

Guastoni A.,University of Padua | Kondo D.,GIA Laboratory | Nestola F.,University of Padua
Gems and Gemology | Year: 2010

Large crystals of the rare-earth carbonates bastnäsite-(Ce) and parisite-(Ce) have been collected from alkaline pegmatites at Malawi's Mt. Malosa, where they occur associated with aegirine, microcline, and several other unusual accessory minerals. Only small portions of some crystals are suitable for cutting into attractive gems, because most of the material is opaque or heavily fractured. This report presents the gemological and chemical properties of Mt. Malosa bastnäsite-(Ce) and parisite-(Ce) gemstones. This area shows good potential for future production of these rare-earth carbonates, although cut stones will continue to be rare. © 2010 Gemological Institute of America.

Marshall D.,Simon Fraser University | Pardieu V.,GIA Laboratory | Loughrey L.,Simon Fraser University | Jones P.,Carleton University | Xue G.,Simon Fraser University
Mineralogical Magazine | Year: 2012

Preliminary geological work on samples from Davdar in China indicate that emerald occurs in quartz veins hosted within upper greenschist grade Permian metasedimentary rocks including quartzite, marble, phyllite and schist. Fluid inclusion studies indicate highly saline fluids ranging from approximately 34 to 41 wt.% NaCl equivalent, with minimal amounts of CO 2 estimated at a mole fraction of 0.003. Fluid inclusion, stable isotope and petrographic studies indicate the Davdar emeralds crystallized from highly saline brines in greenschist facies conditions at a temperature of ∼350°C and a pressure of up to 160 MPa. The highly saline fluid inclusions in the emeralds, the trace-element chemistry and stable isotope signatures indicate that the Davdar emeralds have some similarities to the Khaltaro and Swat Valley emerald deposits in Pakistan, but they show the greatest similarity to neighbouring deposits at Panjshir in Afghanistan. © 2012 Mineralogical Society.

Shigley J.E.,GIA Laboratory | Breeding C.M.,GIA Laboratory
Gems and Gemology | Year: 2015

Diamond color is usually the result of selective absorption of incident white light. The unabsorbed portion of this light is transmitted through the diamond and is interpreted by the human vision system as the perceived color. The spectroscope allows a gemologist to observe some of the more intense and narrower absorptions in the visible spectrum of diamond as dark bands at specific wavelengths. Yet the broader regions of absorption, which can be difficult to observe with the spectroscope, often have a greater influence on a diamond's color. A chart has been prepared to illustrate the visible spectra of various colored diamonds as recorded at low (liquid-nitrogen) temperatures with a spectrophotometer. The chart shows how similar diamond colors can result from different light absorption patterns. © 2015 Gemological Institute of America.

Renfro N.,GIA Laboratory | Koivula J.,GIA Laboratory | Wang W.,GIA Laboratory
Gems and Gemology | Year: 2010

The first decade of the 2000s brought a constant flow of previously known synthetics into the marketplace, but little in the way of new technology. The biggest development was the commercial introduction of faceted single-crystal gem-quality CVD synthetic diamonds. A few other interesting and noteworthy synthetics, such as Malossi hydrothermal synthetic emeralds and Mexifire synthetic opals, also entered the market. Identification of synthetic gem materials continued to be an important function of-and, in some cases, challenge for-gemologists worldwide. © 2010 Gemological Institute of America.

Gaillou E.,Smithsonian Institution | Wang W.,GIA Laboratory | Post J.,Smithsonian Institution | King J.,GIA Laboratory | And 2 more authors.
Gems and Gemology | Year: 2010

Two historic blue diamonds, the Hope and the Wittelsbach-Graff, appeared together for the first time at the Smithsonian Institution in 2010. Both diamonds were apparently purchased in India in the 17th century and later belonged to European royalty. In addition to the parallels in their histories, their comparable color and bright, long-lasting orange-red phosphorescence have led to speculation that these two diamonds might have come from the same piece of rough. Although the diamonds are similar spectroscopically, their dislocation patterns observed with the DiamondView differ in scale and texture, and they do not show the same internal strain features. The results indicate that the two diamonds did not originate from the same crystal, though they likely experienced similar geologic histories. © 2010 Gemological Institute of America.

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