DNA Fingerprinting of Pearls to Determine Their Origins

We report the first successful extraction of oyster DNA from a pearl and use it to identify the source oyster species for the three major pearl-producing oyster species Pinctada margaritifera, P. maxima and P. radiata. Both mitochondrial and nuclear gene fragments could be PCR-amplified and sequenced. A polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay in the internal transcribed spacer (ITS) region was developed and used to identify 18 pearls of unknown origin. A micro-drilling technique was developed to obtain small amounts of DNA while maintaining the commercial value of the pearls. This DNA fingerprinting method could be used to document the source of historic pearls and will provide more transparency for traders and consumers within the pearl industry

Gemmological Investigations on Pearls and Emeralds using Neutron Imaging

Gemmology deals with the characterization of coloured stones, diamonds and pearls used in the jewellery sector. As the investigated objects are in general rather valuable, a large variety of non-destructive testing methods (e.g. X-ray luminescence, X-ray tomography, UV/VIS spectroscopy, etc.) is routinely used for their inspection and characterisation. In a joint project of Paul Scherrer Institut (PSI), Swiss Gemmological Institute (SSEF) and the University Freiburg, potential application fields of neutron imaging methods (i.e. radiography, microtomography and neutron grating interferometry) in the characterisation and testing of pearls and emeralds were investigated and compared to already established X-ray methods. Neutron tomography yields results with comparable image quality but a different contrast, highlighting in the case of pearls the regions containing organic and hence hydrogen containing material. As such regions composed of low-Z material can be very hard to distinguish from voids inside an object using X-ray tomography, neutron tomography provides important additional information on the tested object due to its complementary properties. The complementarity between neutron and X-ray data shows also in the case of emeralds, where fissures filled with organic fillers are highlighted in the neutron data, while staying concealed in the X-ray data. Metallic inclusions in the emeralds on the other hand appear much more pronounced in the X-ray data, then using neutron imaging. The utilization of both methods on the same sample yields hence additional information on the composition of different regions within the object

Petrology, geothermobarometry and geochemistry of granulite facies wall rocks and hosting gneiss of gemstone deposits from the Mogok area (Myanmar)

The Mogok Metamorphic Belt (MMB) of Myanmar formed during the Paleogene collision between the West Burma block and the Shan-Thai block. The MMB is mainly composed of medium to high-grade metamorphic marble, calc-silicate rocks, gneiss, quartzite, peridotite and igneous rocks such as granite, syenite and gabbro. The Mogok area in the central part of the MMB is well-known for magnificent quality ruby, spinel, sapphire, and peridot. To unravel the metamorphic PT-conditions prevailing during the formation of spinel and ruby from primary marble deposits in the Mogok area, three different types of high-grade quartz-garnet gneiss from the neighbourhood of gemstone mines were investigated by electron microprobe. Geothermobarometry reveals granulite facies PT-conditions of 756-792 ◦C at 7.4-7.6 kbar, which is reproduced by Theriak-Domino modelling within the error of both methods at water activities of 0.34-0.4. Shoshonitic and high-K calc-alkaline mafic dykes occur within marble forming conspicuous garnet-nepheline and clinopyroxene-clinoamphibole gneiss. Petrologic and geochemical investigations of these metadykes verify their granulite facies metamorphism and classify them as subduction-related magmatic rocks, which intruded the marble sequences. These investigations as well as previous studies show that spinel and ruby in marble of the Mogok area may have formed not only by metasomatism around alkaline intrusions, but also by granulite facies regional metamorphism

U–pb dating of zircon and zirconolite inclusions in marble-hosted gem-quality ruby and spinel from Mogok, Myanmar

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