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Gem materials

Emmanuel FRITSCH (PR-IMN), Benjamin RONDEAU (MC-LPGN) Olivier SEGURA (PhD student), Aurélien DELAUNAY (PhD student)

Gem materials are known for their luster (diamond), color (ruby, emerald) and high clarity. In general, we strive to understand the properties of these exceptional optical materials, with high added value, and to find the difference between the authentic and the various shades of "fake". We have a keen interest in the origin of the color, which often carries the value, and may be "enhanced" in the laboratory. There are even some gem materials that are naturally thermochromic (chameleon diamonds) or photochromic (sodalite variety hackmanite). Luminescence is sensitive to very low concentrations of defects. It helps detect laboratory treatments sometimes very close to natural processes, especially for colorless diamond. Optical spectroscopies and observation, both non destructive, are our favourite investigation methods.

The orange luminescence of sapphires (Al2O3)
to shortwave ultraviolet (254 nm)
is due to a hole center, whereas the blue color
is emitted by titanate groups.
The photochromic variety of the natural
mineral sodalite, hackmanite, goes
from colorless to deep purple under ultraviolet
radiation, thanks to traces of sulfur.
Natural yellow type Ib diamonds all
correspond to a rare growth morphology,
the reentrant cube, which is rich in H.


  • Emmanuel FRITSCH (PR-IMN), Benjamin RONDEAU (MC-LPGN)
  • Olivier SEGURA (PhD student): natural pearls: properties, structure and identification criteria
  • Aurélien DELAUNAY (PhD student) Near-colorless, type IIa diamonds: natural, synthetic and/or high pressure-high temperature (HPHT) treated.


Gemology, the emerging science of gems
Fritsch E., Rondeau B.. Elements 5 , 147-152 (2009)

Chapter 13: Raman spectroscopy applied to gemology. In "Raman Spectroscopy applied to Earth Sciences and cultural heritage"
Fritsch E., Rondeau B., Hainschwang T., Karampelas S., EMU Notes in Mineralogy, 12, 453–488 (2012)

Luminescence spectroscopy and microscopy applied to the study of gem materials: a case study of C centre containing diamonds.
Hainschwang T, Karampelas S., Fritsch E., Notari F. Mineralogy and Petrology, 107-3, 393-413 (2013)

The origin of color in natural C center bearing diamonds.
Hainschwang T, Fritsch E., Notari F., Rondeau B., Katrusha A. Diamond & Related Materials 39, 27-40 (2013)


  • LPGN, University of Nantes, France
  • GGTL, Geneva, Switzerland and Balzers, Liechtenstein
  • Gübelin Gem Lab, Luzern, Switzerland
  • French Gemmological Laboratory (LFG) and UFBJOP, Paris, France
  • Opalinda, Strasbourg, France

ANR and contracts

Scientific advisor and Course design, LFG, Paris, France.

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