Which impurity is responsible for blue color in type IIb diamonds?

• A. Nitrogen impurities
• B. Hydrogen impurities
• C. Boron impurities
• D. Phosphorus impurities

Answer: (C)

Blue color in type IIb diamonds comes from boron impurities substituting for carbon in the crystal lattice. Boron introduces energy levels that alter how the diamond absorbs light, specifically absorbing red wavelengths and transmitting blue, which gives the gem its distinctive blue hue. This type of diamond is nitrogen-free, distinguishing it from many colorless or yellow-tinted diamonds that owe their color to nitrogen. The other impurities listed don’t produce the blue coloration characteristic of type IIb diamonds; nitrogen tends to create yellow or brown tones, while phosphorus and hydrogen are not the typical culprits for blue in this context.