Type I Diamonds

Type Ia - Nitrogen atoms are present as pairs or small groups called aggregates
Type Ib - Nitrogen atoms are present as isolated atoms

Type IaA - Contain aggregates of two nitrogen atoms, A aggregates
Type IaB - Nitrogen is present as aggregates of four nitrogen toms surrounding a 'vacancy' B aggregates. (Most diamonds containing some nitrogen in the B form also have aggregates of three nitrogen atoms surrounding a vacancy.


It is common to find many diamonds with a mixture of A and B aggregates. These are described as type IaA/B or IaAB.  Type IaAB - Contain both the A and B forms of nitrogen