Which technique is best for determining whether a diamond is Type IIa or Type IIb?

• A. Visual inspection
• B. Spectroscopy
• C. X-ray diffraction
• D. Scanning electron microscopy

Answer: (B)

The main distinction between Type IIa and Type IIb diamonds is the presence or absence of specific impurities in the crystal lattice—nitrogen in Type IIa is essentially undetectable, while Type IIb contains boron, which changes the diamond’s optical and electrical properties. Spectroscopy is the method that reveals these impurity signatures directly. Infrared spectroscopy, in particular, can detect nitrogen-related absorption features and boron-related signals, allowing you to confirm whether nitrogen is essentially absent (Type IIa) or boron is present (Type IIb). Visual inspection can be misleading since both can appear colorless or bluish, and the color alone isn’t a reliable indicator. X-ray diffraction shows the crystal structure but not impurity content, and scanning electron microscopy looks at surface morphology (and, with specialized techniques, elemental composition) rather than the subtle impurity signatures that define these types. So spectroscopy provides the most direct and reliable evidence for distinguishing Type IIa from Type IIb.