The infra-red absorption by diamond and its significance

3. Summary

Approximately ten per cent. of the total number of diamonds form group A and another ten per cent. group B. These two groups exhibit highly contrasting characters. Group A diamonds are isotropic and optically perfect, are opaque to ultra-violet of wavelengths less than 0·3µ and exhibit a visible blue luminescence. Group B diamonds are visibly birefringent, their transparency extends well beyond 0·3µ and they are non-luminescent. The two groups differ strikingly in their infra-red behaviour. These facts taken in conjunction indicate that the two groups of diamond differ fundamentally in their crystal structure.