μ-FTIR mapping: Distribution of impurities in different types of diamond growth

Developments in technology are making the application of Fourier Transform infrared (FTIR) mapping to the study of minerals more feasible. In the case of diamonds, IR spectroscopy provides a simple method of analyzing common impurities; this not only forms the basis of their classification, but may also provide insights into their age and/or thermal history. The spatial distribution of these impurities, as defined by FTIR mapping, thus can reveal significant information about the growth history of the diamond. However, this mapping technique produces thousands of spectra, creating a need for some form of automated data processing, which was previously unavailable. We describe our new computer routine, named DiaMap. It has been written to provide quantitative data on the most commonly reported IR-active impurities in natural diamonds; nitrogen concentrations and aggregation states, the intensity of the platelet (B′) band, and the presence of hydrogen. While this routine is written for application to natural diamonds, it can also be applied to synthetic diamonds. Here we demonstrate the application of the method to a natural diamond of roughly cube morphology from the Diavik mine (Canada) that contains layers of octahedral, cuboid and fibrous growth. The data show that our traditional understanding of nitrogen aggregation rates and platelet development does not apply to cuboid and fibrous diamond growth types, and lays the basis for a more intensive study of such diamonds.