The blue diamond is one of stones the most appreciated to the world.
His(Her,Its) color is due to atoms of Boron or Hydrogen which skipped into the atomic structure.
The most famous of all, are doubtless "Blue Hope" this blue diamond of 45.52ct, which surprises us even today. Of other one diamonds are very known as Wittelsbach-Graff, Oppenheimer Blue or Blue Moon.
Most of the blue diamonds come from mines of South Africa, as mines the First one Mine always in service unlike those of Kimberley and Cullinan.
The diamonds blue of which the color is natural are very rare, most of the time diamonds are treated to obtain this beautiful tint. However any processing must be indicated!
To know more about the mineralogy of the blue diamond, see mindat.org ->
See the article on the Diamant
