gems, corundum, inclusions.5, India.12, Kashmir sapphire, Madagascar.12, Sri Lanka.12, Burma.12, zircon

In this study, zircon inclusions in selected 115 unheated sapphires originating from metamorphic deposits were studied by confocal micro‐Raman spectroscopy. By comparing Raman features of zircon inclusions in gem‐quality sapphires from Myanmar, India (Kashmir), Sri Lanka, and Madagascar, it could be established that those of younger age (sapphires from Myanmar and India [Kashmir]) contain zircon inclusion which exhibit relatively low ʋ1 and ʋ3 band positions and also smaller FWHM (ʋ3) than those in the older sapphires from Sri Lanka and Madagascar. Binary plotting of ʋ1 versus ʋ3 frequencies (Figure 3) and ʋ3 wavenumber versus FWHM of the studied zircon inclusions provide a method to distinguish young sapphires formed during Alpine‐Himalayan orogeny (Kashmir, Myanmar) from those related to the Pan‐African orogeny (Sri Lanka, Madagascar). This study shows the potential of the non‐destructive method on zircon inclusions in sapphires to be used to distinguish their origin as a service to the commercial gem trade. Zircon inclusions in selected 115 unheated sapphires originating from metamorphic deposits—Myanmar, India (Kashmir), Sri Lanka, and Madagascar—were studied by confocal micro‐Raman spectroscopy. This study shows the potential of the non‐destructive method on zircon inclusions in sapphires to be used to distinguish their origin as a service to the commercial gem trade.

gems, diamond, mantle; olivine; ringwoodite; wadsleyite; high pressure-temperature; shear deformation; diamond anvil cell; synchrotron radiation

Synchrotron X-ray diffraction, as well as visual observations, in a diamond anvil cell (DAC) using soft metal gaskets or slightly reducing gas environment, have revealed that the olivine-ringwoodite transition in olivines of several compositions take place in two steps: step 1: displacive restacking of the oxygen layers, followed by step 2: diffusive reordering of the cations. The initiation of the phase transition was observed at temperatures as low as 200°C below the reported temperature for the phase transition under hydrostatic conditions. These observations, especially residual disordered cations, have important implications for deep-focus earthquakes, the ability of ringwoodite to host surprising amounts of water, and possibly the observation of a blue olivine inclusion in a natural diamond from Brazil and in a pallasitic meteorite from Russia.

gems, beryl, emerald, Pakistan, Swat

Swat Valley has become an important source of emeralds, including recently discovered trapiche-type crystals. In this study, emerald samples from Swat were examined by standard gemological testing, UV-Vis-NIR, FTIR, Raman analysis, EDXRF, and LA-ICP-MS. The study found three-phase hexagonal inclusions consisting of water, gaseous carbon dioxide and nitrogen, and a magnesite crystal. The gaseous mixture in two-phase inclusions is characteristic in both trapiche-type (CO₂ + N₂) and non-trapiche samples (CO₂ + N₂ + CH₄). Mineral inclusions of hematite, magnetite, rutile, graphite, and siderite are reported for the first time. Regular non-trapiche-type Swat emeralds contain high chromium (avg. 7471 ppmw), alkali metal (avg. 21,040 ppmw), magnesium (avg. 34,263 ppmw), and iron (avg. 9265 ppmw), as well as scandium (avg. 633 ppmw). Infrared spectra show that the absorption of type II H₂O is stronger than that of type I H₂O. Logarithm plots of trace elements appear to be diagnostic. Based on Raman spectroscopy, the trapiche-type emeralds’ colorless core, light green hexagonal growth zone area, and green rim are emerald, while the six black arms are a mixture of hematite and graphite.

gems, diamond, corundum, inclusions

gems, corundum, inclusions.5, Burma.12, zircon, zirconolite, Mogok, spinel

The Mogok area in Myanmar (Burma) is known since historic times as a source for some of the finest rubies and spinels in the world. In this study, we focus on in-situ U–Pb geochronological analyses of zircon and zirconolite, either present as inclusions in gem-quality ruby and spinel or as accessory minerals in ruby- and spinel-bearing marble and adjacent granulite facies gneisses. The age determination was carried out using both laser ablation inductively coupled plasma time-of-flight mass spectrometry (LA-ICP-TOF-MS) and sector-field mass spectrometry (LA-ICP-SF-MS). In addition, we present multi-element data (REE) of zircon and zirconolite collected with LA-ICP-TOF-MS to further characterize these inclusions. Most of the studied zircon grains display growth zoning (core/rim) regardless if as inclusion in gemstones, or as accessory mineral in host rock samples. U–Pb dating was conducted on both core and rim of zircon grains and revealed most ages ranging from ~200 Ma in the core to ~17 Ma in the rim. The youngest U–Pb ages determined from the rim of zircon inclusions in gem-quality ruby and spinel are 22.26 ± 0.36 Ma and 22.88 ± 0.72 Ma, respectively. This agreement in U–Pb ages is interpreted to indicate a simultaneous formation of ruby and spinel in the Mogok area. In ruby- and spinel-bearing marble from Bawlongyi, the youngest zircon age was determined as 17.11 ± 0.22 Ma. Furthermore, U–Pb age measured on the rim of zircon grains in a biotite-garnet gneiss reveals a Late Oligocene age (26.13 ± 1.24 Ma), however older ages up to Precambrian age were also recorded in the cores of zircon as accessory minerals from this gneiss. These old ages point to a detrital origin of the analysed zircon cores. Although non-matrix matched standard was applied, zirconolite U–Pb age results are narrower in distribution from ~35 Ma to ~17 Ma, falling within the range of zircon ages. Based on results which are well in accordance with previous geochronological data from the Mogok Metamorphic Belt (MMB), we deduce that gem-quality ruby and spinel from Mogok probably formed during a granulite-facies regional metamorphic event in Oligocene to Early Miocene, related to post collision tectonics of the Eurasian and Indian plates. Our data not only provide key information to understand the formation of gem-quality ruby and spinel in the so-called Mogok Stone Tract, but also provide assisting evidence when determining the country of origin of gemstones in gemmological laboratories.

gems, corundum, inclusions.5

Lovely catalog of an exhibition put on by L’École Asia Pacific–School of Jewelry Arts in Hong Kong. The exhibit ran from 10 June to 20 September 2020 and featured inclusion photos from Lotus Gemology’s E. Billie Hughes, Wimon Manorotkul and Richard Hughes, along with essays on various aspects of ruby and sapphire written by Olivier Segura, Capucine Juncker and Billie Hughes, Richard Hughes and Paolo Minieri. The exhibit also offered a collectable series of postcards of inclusion photos.

gems, corundum, sapphire, origin determination, Burma.12, India.12, Kashmir.12, Madagascar.12, Thailand.12, Sri Lanka.12, Nigeria.12, Australia.12, Ethiopia.12, analytical, provenance

Geographic origin determination, one of the most pressing issues facing modern gemological laboratories, is especially challenging for blue sapphire. Reliable origin determination requires careful analysis of a stone’s inclusions and trace element chemistry as well as spectroscopic data. Some stones have characteristic inclusion scenes or trace element chemistry that make it easy to determine their origin, but in many cases there is significant overlap for blue sapphire from distinct geographic localities. The most commonly encountered inclusions are rutile silk and particle clouds. In some stones the silk or clouds may take on a distinct appearance and the origin may be accurately determined. But in many cases the evidence presented by inclusions within a stone is ambiguous. This contribution outlines the methods and criteria used at GIA for geographic origin determination of blue sapphire.

gems, beryl, emerald, Colombia, Muzo, Chivor, Cosquez, Zambia, Afghanistan, Panjshir, Zimbabwe, Brazil, China, Ethiopia

The gem trade has grown to rely on gemological laboratories to provide origin determination services for emeralds and other fine colored stones. In the laboratory, this is mostly accomplished by careful observations of inclusion characteristics, spectroscopic analysis, and trace element profile measurements by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS). Inclusions and spectroscopy can often separate Colombian emeralds from other sources (although there is some overlap between Colombian, Afghan, and Chinese [Davdar] emeralds). For non-Colombian emeralds, trace element analysis by LA-ICP-MS is needed in addition to information from the stone’s inclusions. The relative chemical diversity of emeralds from worldwide deposits allows confidence in origin determination in most cases. This contribution outlines the methods and criteria used at GIA for geographic origin determination for emerald.

gems, spinel, Sri Lanka, inclusions

Sri Lanka has been known for its exceptional spinels for centuries. Most of these beautiful gems are found in colors of red to purple, although some cobalt-bearing blue varieties have been discovered in a few locations. All spinel mining occurs in alluvial deposits in specific areas in the southwestern parts of the island.

gems, corundum, Thailand.12, Inclusions.5

The mineral inclusions of alluvial ruby and sapphire from the Bo Welu gem deposit in Thailand’s Chanthaburi Province were collected and investigated. This deposit is directly related to a basaltic terrain. Raman spectroscopy and electron probe micro-analyzer (EPMA) measurements allow the identification of mineral inclusions of pyrope-rich garnet, sillimanite, high-Al diopside, sapphirine, nepheline, quartz, feldspar (mostly plagioclase), spinel, sulfide, anhydrite, and silicate melts in ruby and purple sapphire. Zircon, alkali feldspar (mostly with high Na content), monazite, columbite, and sulfide were identified in blue sapphire. This study represents the first report of several inclusions in ruby and sapphire from this gem deposit.The mineral inclusions of alluvial ruby and sapphire from the Bo Welu gem deposit in Thailand’s Chanthaburi Province were collected and investigated. This deposit is directly related to a basaltic terrain. Raman spectroscopy and electron probe micro-analyzer (EPMA) measurements allow the identification of mineral inclusions of pyrope-rich garnet, sillimanite, high-Al diopside, sapphirine, nepheline, quartz, feldspar (mostly plagioclase), spinel, sulfide, anhydrite, and silicate melts in ruby and purple sapphire. Zircon, alkali feldspar (mostly with high Na content), monazite, columbite, and sulfide were identified in blue sapphire. This study represents the first report of several inclusions in ruby and sapphire from this gem deposit.