short-wave UV, in addition to occasional blue or red phosphorescence (King et al., 1998). Unlike the DiamondView, gemological UV lamps emit lowerenergy UV radiation and the phosphorescence of type IIb diamonds is not always visible. A few aspects of rough diamond shape and surface texture are strongly indicative of type as well. For example, sorters have recognized that, unlike type I stones, type II diamond crystals typically occur in irregular or flattened shapes and do not exhibit crystallographic faces (Wilks and Wilks, 1991). Sunagawa (2001) suggested that this is due to the latter experiencing greater degrees of fracturing and breakage in their ascent to the earth’s surface during eruptions of kimberlitic or lamproitic magmas, whereas type I diamonds tend to retain their original crystal morphology during magma transport.
Multiple Tests are Optimal When Investigating Diamond Type. Each of the properties and gemological tools mentioned above provides some indication of diamond type without the use of an FTIR spectrometer. They are most powerful, however, when used in combination. For example, type II diamonds can easily be distinguished from type I
on the basis of short-wave UV transparency and strain patterns. Types IIa and IIb can easily be separated on the basis of electrical conductivity. The largest group of natural diamonds, type I, is a bit harder to subdivide, but with practice it is still usually possible. Type Ia diamonds commonly show 415 nm or “cape” lines in the spectroscope, whereas type Ib diamonds often show strong general absorption from