Which statement best describes the origin of many colorless and colored CVD lab-grown diamonds according to the source?

• A. Type Ib
• B. Type IIa
• C. Type Ia
• D. Type IIb

Answer: (C)

Understanding this question starts with how diamonds are classified by nitrogen content and how that nitrogen is arranged in the crystal. Type I diamonds contain nitrogen; Type II diamonds have little or no nitrogen. Within Type I, the nitrogen can be present as isolated atoms (Type Ib) or in aggregated forms (Type Ia), where nitrogen atoms pair up or form larger clusters known as A centers and B centers. These aggregation states influence how the lattice absorbs light and thus affect color.

In chemical vapor deposition (CVD) growth, nitrogen is often incorporated and tends to migrate and cluster into those aggregated forms during the process. That makes Type Ia the most representative classification for many colorless and colored CVD lab-grown diamonds. The aggregated nitrogen in these diamonds can yield colorless stones or various colors depending on the exact aggregation and accompanying defects, whereas Type Ib (isolated nitrogen) or Type IIa (nearly nitrogen-free) would show different typical color behavior and are less characteristic of the common CVD growth outcome. Type IIb involves boron and produces a blue color, which is not as broadly representative of the typical CVD set.