Why Is the Hope Diamond Blue

Diamonds are the only gemstone whose colorlessness enhances their value. However, the rare, rich, natural coloring of fancy color diamonds commands the highest prices. The Hope Diamond possesses exceptional blue coloring and is undoubtedly the most celebrated diamond in the world. What is the origin of its intensely prized blue hue  

Throughout history civilization has treasured the rarity and beauty of fancy colored diamonds. The stunning diamond from India known as the Hope Diamond, once a part of many royal inventories, is now the premier attraction of the Smithsonian Institution (see color Fig. 4.3.1). While the size of the diamond at 45.52 carats has certainly contributed to the public s interest in the gem, the intense blue-violet color of the stone is generally considered to be its most captivating feature. First described in the mid 1600s by the French merchant traveller Jean Baptiste Tavernier as un beau violet (a beautiful violet), the gem also acquired the title Blue Diamond of the Crown or the Royal French Blue when in possession of King Louis XIV of France. The blue color is attributed to trace amounts of boron in the carbon matrix of the stone. Substitution of carbon atoms by nitrogen leads to yellow diamonds, such as the famous canary yellow 128.51-carat Tiffany diamond. 

The chemical composition and crystal structure of a mineral determine its physical and optical properties. The diamond crystalline lattice structure (Fig. 4.3.2) 

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