Geologically Significant Information from Routine Analysis of the Mid-Infrared Spectra of Diamonds

Abstract

Availability of infrared (IR) microscopes has made it possible to obtain absorption spectra from microdiamonds or from small areas of larger diamonds. Analysis of the envelopes of the one-phonon spectra, in terms of the defect-aggregation sequence for ppm quantities of nitrogen present in most diamonds, can be performed. In conjunction with activation energies determined experimentally for the various stages in the sequence, these analyses can be used to obtain time/temperature estimates for diamond residence in the mantle. Such information can be used to distinguish separate diamond populations within and between different geographical and geological diamond sources, depending, of course, on the availability of a sufficient number of diamonds to provide statistically significant information. However, this requires semi-automated procedures for detailed analyses, within a reasonable time, of the large number of spectra necessarily involved. This paper describes some of the practical problems involved and explains current methods of addressing them, for the purpose of specifying a procedure for the extraction of relevant information from the midIR spectra. This is accomplished via Bruker Opus/3D (PCbased) software, followed by transfer to Quattro-pro spreadsheet programs that analyze the data for time/temperature information.