Gem Lab
Raman spectroscopy
With a laser, minerals and even tiny inclusions can be identified without damage. Raman spectroscopy is now a standard tool.
Raman spectroscopy is based on an effect described by the Indian physicist C. V. Raman in 1928: a small part of the light striking a material is scattered with slightly changed energy. The shift depends on vibrations in the crystal lattice and is characteristic of each mineral.
How the measurement is made
A laser is focused through a microscope onto the stone or onto a single inclusion. The scattered light is collected and recorded as a spectrum. Comparison with a reference database shows which mineral it is. The measurement often takes only seconds and is non-destructive.
What Raman is used for
- Identifying the stone: corundum, spinel, garnet or glass can be distinguished quickly
- Identifying inclusions: a crystal inside can be identified without opening the stone; this helps with origin and with detecting heating
- Fillings and coatings: organic substances show their own signals
- Photoluminescence: with the same instrument, defect centres in diamonds that indicate treatment or synthesis can be measured
The limits
Strong fluorescence can mask the weak Raman signal; laboratories then choose a different laser. The surface and the orientation of the crystal affect the spectrum, and in mixtures signals overlap. Raman is not suitable for trace elements and therefore for many questions of origin.
Why the method is so valuable
Inclusions used to be interpreted mainly by their appearance. Today a laboratory can prove that a tiny needle really is rutile or that a crystal is zircon. Such findings make statements in a report more verifiable.
In brief
Raman identifies minerals and individual inclusions non-destructively from their vibrational signature. This makes observations under the microscope verifiable. Trace elements and many questions of origin require other methods.
At NOBILITH
In the Academy, the microscope illustrations explain typical inclusions; in the laboratory such inclusions are confirmed with Raman. The results feed into the report held in the dossier.
Sources
- GIA: Gems & Gemology, articles on Raman spectroscopy
- RRUFF database of Raman reference spectra
Read more
- Laboratory reportsUnderstanding a laboratory reportA laboratory report is a gemstone's most important document. Which information it contains, how to read it and what it does not say.Read more
- KnowledgeWhy a laboratory may say inconclusiveSometimes a question cannot be answered responsibly with the available data. What “inconclusive” means – and what it does not.Read more
- Gem LabGemmological microscopeThe most important instrument in the laboratory: under the microscope, inclusions, growth features and signs of treatment become visible.Read more
- Gem LabRefractometerThe refractometer measures how strongly a stone bends light. This allows many materials to be narrowed down quickly – within clear limits.Read more
Updated 2026-10-06