Like all colored diamonds, blue diamonds derive their color from chemical impurities or defects in the structure of the crystal lattice. Natural blue diamonds are so rare that most jewelers have never seen one. It has been estimated that the earth produces one colored diamond for every 10,000 white diamonds.
During formation, Boron bonds with Carbon and causes the crystal lattice to absorb red, green, and yellow light. Blue diamonds and diamonds with a secondary hue of blue can be found in Brazil, Central and South Africa, and fine dark blue can be found in India. Blue diamonds typically display red fluorescence with exposure to utlraviolet light and helps prove a stone to be of natural origins.
The Hope Diamond, 45.52 Fancy Dark Grayish Blue Diamond
The Hope Diamond is one of the most famous blue diamonds ever mined. It is currently on display at the National Gem and Mineral collection at the National Natural History Museum in Washington, D.C. and owned by the Smithsonian Institution. The diamond was thought to have been originally discovered in the mid-1600s in India and then sold to King Louis XIV around 1669 and became known as "Le bleu de France". It was later purchased in 1839 by a banker by the name of Henry Thomas Hope and renamed the "Hope diamond" after falling into the Hope family.
Fun fact: Gloria Stuart, nominee for best supporting actress for Titanic, wore the most expensive single piece of jewelry ever worn to the Oscars in 1998. It was a Harry Winston 15-carat blue diamond necklace worth $20 million!