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Hanco Zwaan

Dr. J.C. (Hanco) Zwaan FGA, Senior researcher - Taxonomy and Systematics


Email: hanco.zwaan@naturalis.nl
Phone: +31 (0)71 56 87 665
Room number: C01.14, Darwinweg 2
“I am fascinated by the hidden treasures of Natural History. ”

My interest in minerals started at a young age, when I was primarily interested in their use in society and how I could identify them. It gradually developed into a desire to understand the factors that shape “System Earth” and what it takes to form minerals, the small building blocks. In particular I became fascinated by specific processes that produce beautiful, durable and rare minerals, called gemstones. Applying this knowledge in our lab, by distinguishing those unique items from the many look-a-likes or enhanced stones produced, also got me interested in the formation of pearls that consist of minerals that are produced by living organisms. I love to share my ‘hunt for treasure’ not only with fellow-scientists, but also with a wide audience, including gem- and antique dealers, jewelers, and other gem-enthusiasts.  


At Naturalis, I hold a position as research scientist. I am also head of the Netherlands Gemmological Laboratory.  I have a PhD from Free University of Amsterdam on Geology, specializing on the formation of emeralds.

Apart from being an expert on the formation of gems, I also published articles on a variety of other gemmological and mineralogical topics. I co-authored the Edward Gübelin Most Valuable  Article of the Year Award 2008 – first prize winning article ‘Copper-bearing (Paraíba-type) Tourmaline from Mozambique’, and the 2012 – third prize winning article ‘Emeralds from the Fazenda Bonfim Region, RGN, Brazil’,  that appeared in Gems & Gemology.

I am currently president of the World Jewellery Confederation (CIBJO) gemmological commission, dealing with nomenclature issues and laboratory best practices, secretary of the Dr. Schürmannfonds foundation, Executive Committee member of the International Gemmological Conference (IGC), and member of the Dutch NEN norm commission, dealing with the European ISO/CEN standard on Consumer confidence and nomenclature in the diamond industry.  


Research interest

The focus of all studies is on gems and pearls. My main research interest is to understand the specific processes that lead to the formation of gems, and how these processes link to specific events in the regional geologic history. This information can be used to better constrain ‘origin-specific’ properties that need to be determined when the (geographical) origin of a faceted gem has to be assigned. Further questions in this respect are whether this is feasible in all cases, and what is exactly needed to substantiate claims on origin of not only gems, but also pearls. These questions are relevant, in relation to fair-trade, sustainability issues and nature conservation. 



geology, gem provenance, advanced gemmology, education, applied research

Current research topics

Genesis of gems in crustal regions


The case of Sri Lanka: the formation of sapphires in lower crust

Relatively few data exist  on primary corundum (sapphire) occurrences, because most sapphires are found in alluvial deposits, transported away from the primary source. Young, Cenozoic (primary) magmatic occurrences are studied most. In contrast, models of corundum formation in metamorphic and metasomatic occurrences generally are of a hypothetical nature and poorly constrained by empirical facts. Details on the geological context, growth mechanisms and the origin of reactive fluids are scarce. During  field work last year, we identified  rare primary sapphire occurrences in Sri Lanka that can be studied in their geological context. It is expected that this study will lead to new insights into how sapphires are formed and how this process is linked to the geologic history of Sri Lanka in the late-Precambrian, still early history of the Earth. These data will be linked to what is known about gem occurrences in other parts of the super continent Gondwana (southern India, Madagascar, Mozambique, Tanzania) that was formed at the end of the Precambrian.

The case of Brazil: the formation of emeralds in upper crust

Models of emerald formation are fairly well established; however, conditions and mechanisms of emerald growth may differ greatly and objective observations may lead to more or other models. My work in Zimbabwe showed a new mode of emerald formation, namely emerald formation as a product of contact metasomatism at the border of ultramafic rocks and rare-element pegmatites during a deformation event, involving late stage magmatic/hydrothermal activity channelled by shearing.  At Sandawana, Zimbabwe, this took place at the border of  a major Late Archaean suture zone. The model did not fit in any of the genetic classification schemes presented before and this study also underscored that no single theory or model can be applied to all ‘schist-type’ emerald deposits. 

Key in the case of a new emerald occurrence in Rio Grande do Norte, Brazil, is to what extent the formation of emeralds is influenced by regional geological events, and under what specific conditions (chemistry-temperature-pressure-time) it has been formed. To what extent do the formation conditions differ from those in other areas? The case can further be compared with well-studied other cases in Africa, Russia and Brazil.

In the framework of the Nederlands Edelsteen Laboratorium (Netherlands Gemmological Laboratory) the identification of gemstones and pearls is part of the daily work. One of the ongoing research projects here is the systematic characterisation of coloured gemstones from geologically different occurrences.

Netherlands Gemmological Laboratory

The Netherlands Gemmological Laboratory offers identification and grading services to Jewellers, Auction Houses, dealers, and consumers. Reports are issued on diamonds, coloured gemstones and pearls. Diamonds are graded according to international standards; the weight in carats, the colour, clarity and quality of the cut are evaluated. All these factors are important when the value has to be established of a particular stone. Because diamond is a valuable commodity, it is frequently simulated by other products, like synthetic cubic zirconia and synthetic moissanite.

Other gems, like ruby, sapphire and emerald, are frequently treated in order to enhance their appearance (colour and/or clarity), but also synthesized or simulated. So for each gemstone various categories exist, each representing a different value, for instance ‘natural ruby’, ‘enhanced ruby’, ‘treated ruby’, ‘synthetic ruby’ and imitation of ruby (often glass). In view of the difficulties in describing and identifying a gemstone correctly, the Netherlands Gemmological Laboratory is frequently asked for advice.

The Lab is independent and not involved in trading. It can therefore give an objective description and scientifically sound opinion on the quality and, where possible, provenance of any gem material that is offered for examination. The reports issued are internationally recognized and do not include valuation. In addition to relatively simple instruments used in earlier days, such as a refractometer, polariscope, and microscope, the laboratory (like other major gemmological laboratories in the world) houses more advanced technology. Ultraviolet-Visible (UV-VIS) and Fourier Transform Infrared (FTIR) spectrometers are used to measure absorption (or transmission) spectra of gemstones in the ultraviolet, visible and infrared frequencies, which helps to detect treatments and to ascertain the origin of a gem. A Raman micro-spectrometer, using the frequencies caused by the Raman effect, helps to identify minerals, inclusions, and various, otherwise undetectable treatments, and energy dispersive X-Ray Fluorescence (micro-EDXRF) is used for non-destructive chemical analysis of gemstones. Additionally, radiography, X-Ray Diffraction and micro computer tomography techniques are used for pearl testing. 

Other activities include public lectures and various courses and seminars designed for professional jewellers and others, also in cooperation with the School for Gold- and Silversmiths and Jewellers (Schoonhoven). There is a strong link between the Lab, the collections, research, and public activities. The historical collections (e.g., gems donated by King William I) provide invaluable reference material for natural gemstones.

more information about the Netherlands Gemmological Laboratory


The project in Sri Lanka is carried out in collaboration with Leo Kriegsman (Naturalis), Gamini Zoysa, Colombo, partners at Peradeniya University, and the Geological Survey, all in Sri Lanka, University of Perth, Australia, and Joh.Gutenburg University, Mainz. 

The project in Brazil will be carried out in collaboration with partners at the University of Natal, Rio Grande do Norte, Brazil, and the Joh.Gutenburg University, Mainz, Germany. 

Facilities at the University of Utrecht will be used in both projects.



Foundation and Diploma in Gemmology (FGA - BSc. eq.)

Last year the Netherlands Gemmological Lab became an Allied Teaching Centre of Gem-A, London, and started to provide an internationally recognised education program in gemmology, leading to an accredited, equivalent to BSc., Degree in Gemmology. Students passing the exams receive the title FGA (Fellow of the Gemmological Association of Great Britain).   

European degree in gemmology (EG - HBO eq.)

I am also involved in vocational teaching (cooperation with the Vakschool, Schoonhoven) leading to a HBO equivalent European degree in gemmology (FEEG, Federation of European Education in Gemmology). Students passing the exams receive the titel EG (European Gemmologist).

Short courses in gemmology

Short practical courses designed for gem and jewellery professionals. For further information go to  Netherlands Gemmological Laboratory (information in Dutch).

Supervision BSc Students

2013 Supervisor - Weerd, E. de - Phylogenetic implications of calcium carbonate mineralogy and pigment types in coral
2011 Co-supervisor - Graaf L. van de - Inventory of Baltic amber fossils using modern techniques
Available student projects



Journals SCI, peer-reviewed

Zwaan J.C., Hawthorne F.C., Day M., Laurs B.M. 2018. Cat’s-eye Tremolite from Badakhshan, Afghanistan. Journal of Gemmology 36: 14-15.

Zwaan J.C., Laurs B.M. 2018. Yellow scapolite from Tanzania showing peculiar daylight fluorescence. Journal of Gemmology 36: 198-200.

Zwaan J.C., Falster A.U., Simmons W.B., Laurs B.M. 2018. Axinite-(Mg) from Parachinar, Pakistan. Journal of Gemmology 36: 281-283.

Zwaan J.C., Mertz-Kraus R., Renfro N.D., McClure S.F., Laurs B.M. 2018. Rhodochrosite Gems: Properties and Provenance. Journal of Gemmology 36: 332-345.


Journals SCI, peer-reviewed

Zwaan J.C., Deljanin B. 2017. A Research Facility in The Netherlands for the HPHT Growth of Synthetic Diamonds and HPHT Treatment. Journal of Gemmology 35: 491-494.

Schilthuizen M., Sipman I., Zwaan J.C. 2017. Sexual dimorphism in shell coloration of Pletostoma (Caenogastropoda: Diplommatinidae) is caused by polyenes. Journal of Molluscan Studies: 1-3.
Go to website (URI)

Zwaan J.C. 2017. Enstatite from Emali, Kenya. Journal of Gemmology 35: 575-576.

Schilthuizen M., Sipman I., Zwaan H. 2017. Sexual dimorphism in shell coloration of Plectostoma (Caenogastropoda: Diplommatinidae) is caused by polyenes. Journal of Molluscan Studies: pending.
Go to website (DOI)

Chapters in books

Zwaan J.C., Swaving C., In: Eds. van den Bercken B.J.L., Baan V.C.P. 2017. The Original RMO Engraved Gem Collection: Gem Identification and Applied Research Techniques. Palma: Papers on Archaeology of the Leiden Museum of Antiquities 14 Palma 14 - Papers on Archaeology of the Leiden Museum of Antiquities 65-74: Sidestone press, Leiden. ISBN 978-90-8890-505-6.
Go to website (URI)


Journals SCI, peer-reviewed

Zwaan J.C., Pezzotta F., Rossmann G.R. 2016. Orange-Red to Yellowish Brown Cordierite from Madagascar. Journal of Gemmology 35: 8-9.

Zwaan J.C., Falster A.U., Simmons W.B., Blauwet D. 2016. Tantalite-(Mn) from Grangal, Nuristan, Afghanistan. Journal of Gemmology 35: 111-114.

Zwaan J.C. 2016. Clinohumite from Vietnam. Journal of Gemmology 35: 279-280.

Zwaan J.C. 2016. Scapolite from Badakhshan, Afghanistan. Journal of Gemmology 35: 285-287.

Zwaan J.C. 2016. Cat’s-eye Väyrynenite from Pakistan. Journal of Gemmology 35: 288-289.


Journals SCI, peer-reviewed

Reich S., Warter V., Wesselingh F.P., Zwaan J.C., Laurens L., Renema W. 2015. Paleoecological significance of stable isotope ratios in Miocene tropical shallow marine habitats (Indonesia). Palaios 30: 53-65.
Go to website (DOI)

Zwaan J.C. 2015. Yellow Scheelite from Khaplu, Pakistan. Journal of Gemmology 34: 298-299.

Zwaan J.C. 2015. Apatite from Kenya. Journal of Gemmology 34: 289-290.

Zwaan J.C. 2015. Rhodochrosite from Brazil. Journal of Gemmology 34: 473-475.

Zwaan J.C., Hawthorne F.C. 2015. Tremolite from Mwajanga, Tanzania. Journal of Gemmology 34: 569-571.

Zwaan J.C. 2015. Stabilized Shattuckite and Bisbeeite from the Democratic Republic of Congo. Journal of Gemmology 34: 663-666.

Zwaan J.C. 2015. Purple Tourmaline from Maraca, Mozambique. Journal of Gemmology 34: 666-667.

Zwaan J.C. 2015. Green Prase Opal from the Kondoa District, Tanzania. Journal of Gemmology 34: 658-660.

Zwaan J.C., Buter E., Mertz-Kraus R., Kane R.E. 2015. Alluvial Sapphires from Montana: Inclusions, Geochemistry and Indications of a Metasomatic Origin . Gems & Gemology 51: 370-391.
Go to website (DOI)


Journals non-SCI, peer-reviewed

Zwaan J.C., Groenenboom P. 2014. Natural pearls from Edible 'True Oysters' in Zeeland, the Netherlands. Journal of Gemmology 34: 150-155.

Zwaan J.C., Marel D.M. van der, Dommisse H.A. 2014. The ‘Sleeping Lion’ Baroque Pearl: An Update. Journal of Gemmology 34: 248-253.
Go to website (DOI)

Zwaan J.C. 2014. Gem Notes: Green Fluorite from Stak Nala, Pakistan. Journal of Gemmology 34: 192-194.

Zwaan J.C. 2014. Gem Notes: Bicoloured Grossular from Kambanga, Kenya. Journal of Gemmology 34: 195-197.

Zwaan J.C. 2014. Gem Notes: Blue Kyanite from Tanzania. Journal of Gemmology 34: 198-200.

Edited books

Lauwerier R.C.G.M., Kort J.W. de, (eds.). 2014. Merovingers in een villa 2. Romeinse villa en Merovingisch grafveld Borgharen – Pasestraat Onderzoek 2012. 237 p. Rijksdienst voor het Cultureel Erfgoed, Amersfoort. ISBN 9789057992346.
Go to website (URI)

Chapters in books

Jagt I. M. van der, M., Laarman F. J., Kuijper W., Nieman A. M., Os B. J. H. de, Zwaan J.C. 2014. Dierlijk Materiaal. 157-189: Rijksdienst voor het Cultureel Erfgoed, Amersfoort, Amersfoort. ISBN 9789057992346.
Go to website (URI)


Journals SCI, peer-reviewed

Zwaan J.C., Jacob D.E., Haeger T., Cavalcanti Neto M.T.O., Kanis J. 2012. Emeralds from the Fazenda Bonfim Region, Rio Grande do Norte, Brazil. Gems & Gemology 48: 2-17.
Go to website (DOI)


Journals non-SCI, peer-reviewed

Zwaan J.C., Dommisse H.A. 2009. A description and history of one of the largest nacreous pearls in the world. Journal of Gemmology 31: 196-202.


Journals SCI, peer-reviewed

Houran J., Laurs B.M., Krzemnicki M.S., Groenenboom P., Kondo D.M., Haenni H.A., Laurs B.M., Hlaing U.T., Win K.K. Fernandes S., Laurs B.M., Zwaan J.C., Koivula J.I., Chadwick K.M., Choudhary G., Overton T.W. 2008. Colored stones and organic materials. Gems & Gemology 44: 262-281.

Laurs B.M., Zwaan J.C., Breeding C.M., Simmons W.B., Beaton D., Rijsdijk K.F., Befi R., Falster A.U. 2008. Copper-bearing (Paraiba-type) tourmaline from Mozambique. Gems & Gemology 44: 4-30.

Laurs B.M., Zwaan J.C., Simmons W.B., Falster A.U. 2008. Tourmaline from Muva, Mozambique. Gems & Gemology 44: 273-275.

Journals non-SCI, peer-reviewed

Zwaan J.C., Zoysa E.G. 2008. New primary gem occurrences in Sri Lanka. Gemmologie: Zeitschrift der Deutschen Gemmologischen Gesellschaft 57: 23-32.


Journals SCI, peer-reviewed

Laurs B.M., Zwaan J.C., 2007. Field study on Cu-bearing tourmaline mines in Mozambique. Gems & Gemology 43: 383-384.

Journals non-SCI, peer-reviewed

Zwaan J.C. 2007. Models of emerald formation: a new perspective. Gemmologie: Zeitschrift der Deutschen Gemmologischen Gesellschaft 56: 71-74.


Journals non-SCI, peer-reviewed

Zwaan J.C. 2006. Gemmology, geology and origin of the Sandawana emerald deposits, Zimbabwe. Scripta Geologica 131: 1-211.


Journals SCI, peer-reviewed

Zwaan J.C., Seifert A.V., Vrana S., Laurs B.M., Anckar B., Simmons W.B.S., Falster A.U., Lustenhouwer W.J., Muhlmeister S., Koivula J.I., Garcia-Guillerminet H. 2005. Emeralds from the Kafubu area, Zambia. Gems & Gemology 41: 116-148.


Journals SCI, peer-reviewed

Zwaan J.C., Cheilletz A., Taylor B.E. 2004. Tracing the emerald origin by oxygen isotope data: the case of Sandawana, Zimbabwe. Comptes Rendus Geoscience 336: 41-48.
Go to website (DOI)

Journals non-SCI, peer-reviewed

Seifert A.V., Zacek V., Vrana S., Pecina V., Zacharias J., Zwaan J.C. 2004. Emerald mineralization in the Kafubu area, Zambia. Bulletin of Geosciences 79: 1-40.


Journals SCI, peer-reviewed

Calligaro T., Dran J.C., Poirot J.P., Querre G., Salomon J., Zwaan J.C. 2000. PIXE/PIGE characterisation of emeralds using an external micro-beam. Nuclear Instruments & Methods in Physics Research Section B-Beam Interactions with Materials and Atoms 161: 769-774.
Go to website (DOI)

Naturalis Repository

Please contact the author when you are interested in one of the articles above and it is not available online or in the repository.