Lot Essay
"Blue diamonds rarely have the depth of colour of a sapphire, and some show a hint of gray. As nitrogen is much more common and abundant than boron in diamonds, natural blue diamonds are quite rare"
George E. Harlow, The Nature of Diamonds, Cambridge University Press, 1998, p. 41
George E. Harlow, The Nature of Diamonds, Cambridge University Press, 1998, p. 41