Fine pearls are natural pearls (formed without human intervention), a limestone concretion produced by a mollusc in seawater or fresh water. There are a variety of main places of production for fine pearls such as the Persian Gulf, Australia or Polynesia. However, natural pearls can be found in all parts of the world.

There exist two types of fine pearls: Nacreous pearls and non-nacreous pearls. Nacreous pearls are made of mother-of-pearl (arrangement of calcite and/or aragonite interconnected by protein materials). Non-nacreous pearls are made of disorganised calcites and/or aragonite such as layers of mother-of-pearl.

Laboratory analysis of fine pearls is carried out via microradiography/tomography to observe their internal structure. X-ray luminescence, chemical and spectrometric studies will refine the diagnosis concerning the origin of the colour and the environment in which the pearl was created.


  • Name: fine pearls
  • Mineralogical nature: Biomineralisation
  • Colour: White, cream white, yellow, brown, grey, black
  • Crystal system: Calcareous concretion produced by a mollusc without human intervention
  • Chemical composition: CaCO3
  • Causes of colour: Natural pigments
  • Density: 2.66 to 2.68
  • Hardness: 3
  • Cleavage: None
  • Fracture: Splintering
  • Refractive index: n: 1.530 to 1.680 (use of the index is not recommended)
    Dispersion: Opaque
  • Pleochroism: Opaque
  • UVL: White to yellow to milky blue, orange to medium red for Pteria Sterna pearls
  • UVC: Same, lower
  • Treatments: Irradiation
  • Syntheses: None, beware of imitations
  • Geographical origin: Bahrain, Polynesia, Persian Gulf, Mexico, Australia, Philippines, Indonesia, etc.
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