Hanco Zwaan

Hanco Zwaan

Working on understanding the factors that shape “System Earth” and what it takes to form minerals, the small building blocks, lead to a particular fascination for specific geological processes that produced beautiful, durable and rare minerals, called gemstones. Expertise on these hidden treasures of Natural History is used in our gemmological laboratory, when distinguishing those unique items from the many look-a-likes, synthetics or enhanced stones produced. 


Geology, gem provenance, gem origin, advanced gemmology, applied research, pearl testing, mineralisation, bio-mineralisation, education

Dr. Hanco Zwaan FGA

Researcher and Head NEL
Taxonomy & systematics

+31 (0)71 751 9665

Nederlands Edelsteen Laboratorium (NEL)



The focus of all studies is on the formation and identification of gemstones and pearls. Key is the understanding of mineralization and biomineralization.

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. 

rutile needles in sapphire
two phase inclusions in flux-grown emerald



  • 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. 
  • 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) 
  • 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., 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)

  • 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.

  • 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.

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

  • 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.

  • 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)

  • Seifert A.V., Zacek V., Vrana S., Pecina V., Zacharias J., Zwaan J.C. 2004. Emerald mineralization in the Kafubu area, Zambia. Bulletin of Geosciences79: 1-40.

  • 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)


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

The Netherlands Gemmological Laboratory (NEL) is an Accredited Teaching Centre of Gem-A, London, and provides 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.)

The NEL is 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).

In the

Volkskrant 2018 - 8 februari 2018: 'Bling bling uit het lab', interview over de opkomst van de synthetische diamant.

metallic flux in synthetic diamond