Ruby is the red variety of the corundum (aluminium oxide or alumina). It is coloured by chromium. The formation of rubies can be divided into several groups: rubies of metamorphic origin, rubies of metasomatic origin and rubies of basaltic origin. Each type of ruby will have different properties (spectrometry and chemistry in particular).

All rubies submitted to the Laboratory are analysed to identify their nature. As synthetic rubies have been in existence since the end of the 19th century, it is essential that they be differentiate them from natural rubies based on their inclusions, properties and very different chemistries.

Thermal treatment of ruby is a traditional practice detected in the laboratory by analysing the inclusions and spectra gained on each stone analysed. Other ruby treatments exist such as filling cracks with lead-doped or lead-free glass. Of course, all treatment on stones identified during our analyses is indicated in our reports.

The geographical origin of rubies is determined based on a set of arguments deduced from our analyses: identification of inclusions, spectrometry, chemical study. The experience of our gem specialists and the resulting rigour of our quality procedures are undeniable strengths in the conclusions drawn on our reports.


  • Name: Ruby
  • Mineralogical nature: Corundum
  • Colour: Red to red-purple (sometimes asterism or trapiche)
  • Crystal system: Rhombohedral
  • Chemical composition: Al2O3
  • Causes of colour: Cr3+
  • Physical properties:
  • Density: 3.97 to 04:05
  • Hardness: 9
  • Cleavage: None
  • Fracture: Conchoidal or irregular
  • Optic sign: Negative Uniaxial
  • Refractive index: no: 1.767 to 1.778 / ne: 1.759 to 1.770
  • Birefringence: 0.008 to 0.009
  • Dispersion: 0.018
  • Pleochroism: Clean red-orange to red-purple
  • UVL: Inert to intense red
  • UVC: Inert to medium red
  • Treatments: Thermal treatment
  • Deep diffusion with Be2+
  • Filling with glass, possibly doped with non-Pb3+
  • Syntheses: Merger (Verneuil process, Czochralski, etc.)
  • Anhydrous Dissolution
    Hydrothermal Dissolution
  • Geographical origin: Myanmar, Madagascar, Mozambique, Tanzania, Kenya, Pakistan, Afghanistan, Greenland, Sri Lanka, Vietnam, etc.


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