The lecture was delivered on the 8th December, 2004 at AIGS by Dietmar Schwarz and Christian Dunaigre, Gubelin Gem Lab, Switzerland.
In brief:
Historical data: The concept of country of origin determination started 60+ years ago in Switzerland by Dr. Eduard Gubelin who did methodical studies on internal features of gemstones originating from important gem localities around the world. During 1950s and 1970s the number of important gem deposits were restricted due to political and economic reasons. Some of the major deposits include:
Ruby: Ratnapura/Elahera in Sri Lanka
Mogok Stone Tract / Mong Hshu / Namya in Burma
Trat province in Thailand
Magari / Umba valley in East Africa
Different localities in Vietnam
Different localities in Madagascar
Sapphires: Ratnapura / Elahera in Sri Lanka
Mogok Stone Tract in Burma
Kanchanaburi / Chantaburi in Thailand
Different localities in Australia
Different localities in Madagascar
Different localities in the USA
Emeralds: Muzo / Chivor in Colombia
Different localities in Zambia
Sandawana in Zimbabwe
Ural mountains in Russia
Different localities in Brazil
Different localities in Afghanistan
Different localities in Pakistan
In today’s gem market, traders like to submit a ruby, sapphire or emerald for origin determination due to its high value. Inclusions do affect prices. There are number of reasons why inclusions alone are unreliable for determining the origin of gemstones. The current gemological knowledge of inclusions for various ruby + sapphire + emerald + other important colored stone occurrences are incomplete. Study of inclusions is a relatively new science and there is so much that remains to be learned + so many inclusions that have yet to be identified and catalogued. The key areas to be studied are:
- variation of the inclusion parameters within samples from a given locality
- similarity of inclusion populations in samples from different localities
- what sort of diagnostic origin information can we collect from a cut gemstone
- limitations in the determination of origin
- chemical fingerprinting
- advanced instruments such as UV, VIS-NIR, FTIR, Raman +++
During the 80s and 90s many new gem deposits were discovered. It was found that the mineralogical-gemological properties of the new sources were quite similar or even identical to those observed from the traditional sources. For instance blue sapphires from Madagascar displayed features that resembled sapphires from Sri Lanka, East Africa, Burma or even Kashmir. At the same time gemstones even when found in similar geological environments still showed some locality-specific features which allowed a clear separation from gems originating from a deposit of the same generic type such rubies from the Mogok and Mong Hshu.
Today gemological laboratories dealing with origin determination of colored stones are confronted with the gem production of an increasing number of mining areas all over the world. Some of the traditional sources are not producing gems consistently. Without any doubt the island of Madagascar has enormous potential for almost all gemstone species located in different regions of the country and related to different types of host rocks. Advanced + proprietary treatment techniques in rubies, sapphires and emerald may result in the elimination of characteristic features and make origin determination more difficult.
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