arrangements characteristic of synthetic diamonds. Several natural diamond types also show characteristic fluorescence patterns in the DiamondView (GIA staff observations; figure 11). Type Ia diamonds usually show blue fluorescence with irregular natural growth patterns. Natural type Ib diamonds often show an array of green luminescence lines on a background of orange fluorescence, whereas their synthetic counterparts often show greenish yellow and blue fluorescent growth zones in cross-like patterns (Shigley et al., 2004). Type IIa and IIb diamonds usually show a network of crisscrossing features that are thought to be due to dislocations in the diamond lattice. In addition, type IIb diamonds nearly always show blue or red phosphorescence in the DiamondView. Blue phosphorescence alone should not be used as evidence for diamond origin, because boron impurities in type II HPHT-grown synthetic diamonds will also produce blue phosphorescence.