5th European Gemmological Symposium

Last Updated: 31st Aug 2013

The 5th European Gemmological Symposium took place on last 16th June 2013 in Leiden, The Netherlands, at the Museum of Natural History.
A short summary of the speeches is given in the following lines.
"OVERVIEW OF PEARL TESTING; CLASSIC METHODS AND NEW DEVELOPMENTS" by Stefanos Karampelas, Luzern, Switzerland. He emphasized the new challenges of testing pearls, which nowadays regards not only whether a specimen is natural, cultured or an imitation, but also whether it comes from a mollusk which is included in the CITES list, i.e. whether it belongs to en endangered specie. Therefore the issue is also whether a pearl was acquired before or after the mollusk was inserted in the CITES list. For example, the famous pink "conch" pearls come from the mollusk Strombus pugilis which was included in the CITES list in 2006. Therefore the issue is whether a conch pearl was acquired before or after that date. Just radioactive element analyses (for example the 14-C) may give an answer.
"COLOUR AND COLOUR MODIFICATION OF NON-TRANSPARENT QUARTZES" by Ulrich Henn, Idar-Oberstein, Germany. He gave an oversight of non-transparent quartz varieties with the gemmological and the business names, thus stressing the causes of colours are colour centers, optical effects and inclusions. He gave also an oversight of colour enhancements in agates and in other kinds of quartzes.
"USEFUL GEMMOLOGICAL DATA SETS FROM DEPOSIT SPECIFIC SAMPLES" by Kenneth Scarratt, Gemological Institute of America. He gave an oversight of examples of inclusions in several gemstones (corundums, beryl etc.), thus stressing some inclusions may be somewhat informative about the possible origin of a gemstone, even if not always decisive. For example some African corundums were found to have an inclusion combination which is very similar to the inclusions showm in Burmese rubies and sapphires, and some African and Afghani emeralds showed inclusions which were very similar to those which often appear in the Columbian stones. Just a spectrometrical analysis may give an answer to this issue.
"NATURAL GREEN DIAMONDS" by Thomas Hainschwang, Balzers, Liechtenstein. He talked about the causes of green colour in natural and artificially enhanced diamonds, by giving much importance to natural and artificial irradiation. Natural irradiation may be given by contact with natural radioactive minerals and/or fluids. He also told it's very difficult even for gemmologists to distinguish a natural green diamond from an artificially irradiated one. The conclusion is the only green diamonds which have an unambiguously natural colour are those which have been kept in museums uninterruptedly since 1930 or even before.
"ELEMENT ANALYTICAL AND UV-VIS-NIR STUDY OF NATURAL UNTREATED SPINELS FROM VIETNAM IN COMPARISON TO SYNTHETICS" by Tobias Hàger, Mainz, Germany. He gave an oversight of Vietnamese red and blue spinels which were recently found in several localities of that country, and showed the results of a quantitative analysis of colouring elements on those stones and, by comparison, on some synthetic ones. The result for the natural red spinels versus the synthetic ones was a slight difference in spectrum for the elements vanadium, chrome and iron, and for the natural blue spinels versus the lab created ones was a slight difference in spectrum for the elements cobalt and iron.
"THE ORDINARY AND EXTRAORDINARY SHAPES OF DIAMOND CRYSTALS" by Emanuel Fritsch, Nantes, France. He showed the various forms of diamond crystals, from the usual ones to the strangest ones, thus giving an oversight of growth ways in natural and synthetic diamonds. Natural diamonds show an octahedrical (111), fibrous and/or cuboid growth, or a combination of those ways (a photo of a strange diamond crystal was shown, this crystal showed four perpendicular rounded "discs" in the places of the octahedron edges), while synthetic ones show faces which are absent in natural crystals: true cube (001), dodecaedron (110) and trapezoedra (113) and (115). An analysis at the luminescence and at the microscope should give an answer.
"GEMMOLOGY AND GEOLOGY OF PRECIOUS OPAL DEPOSITS: COMPARISON OF AUSTRALIAN VERSUS ETHIOPIAN DEPOSITS" by Benjamin Rondeau, Nantes, France. He talked at first about the recent discovery of opals in the Wegel Tana deposit in Ethiopia, thus stressing the stones are found in a relatively low depth and therefore show inclusions of vegetable residuals (roots), while the famous Australian opals are found in a much bigger depth and therefore they replace fossils (for example shells), but they don't contain organic residuals inside the stone. He also gave an oversight about the stability of those gemstones, thus stressing Ethiopian cutters are not aware of the danger of breaking the stones while cutting them as the Australian cutters are.
"AMBER: REAL, FAKE AND COLOURED" by Maggie Campbell, London, United Kingdom. She talked at first about recent discoveries of amber deposits (Australia), thus stressing the Australian ambers are very similar to the Burmese ones regarding their colour (red to pink). She also stressed the new challenge of terminology, thus wondering when a specimen should be called "amber" and when should it be called "copal". So far the gemmologists gave an age limit for amber and copal, but recently a resin was found in Ethiopia, which was dated over 90 million years old, which melted easily when polished, as well as copal usually does. Therefore the concept should be discussed. Moreover some copal is treated in autoclave in order to have it "matured", i.e. to increase the melting point of it. Therefore it is not an amber, but it is an artificially enhanced copal. The challenge is to have a method to distinguish the specimen. Then she gave an oversight of artificially coloured resins (for example the "green amber" and the "Baltic cherry amber"), and of fakes which are marketed with the false name "amber", for example bakelite, a material which has nothing to deal with amber, whose marketing name is often "Vintage red cherry amber bakelite".
Riccardo Modanesi.





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