Synopses: The value of infra-red spectra in identifying sulphide minerals has been assessed by surveying the spectra of some forty specimens. Spectra of finely ground samples dispersed in polyethylene discs were obtained in the region 420-90 cm−1 with a resolution of 3–4 cm−1, using a Beckman-RIIC Fourier-Transform Interferometer. Except for minerals whose metallic conductivity obliterated vibrational features, the spectra permitted rapid recognition of sulphide minerals either alone or in mixtures.
Spectra of the following twenty-five pure, or nearly pure specimens are presented: cinnabar, galena, pyrrhotine, alabandine, sphalerite, wurtzite, realgar, orpiment, stibnite, bismuthinite, arsenopyrite, tetrahedrite, pyrargyrite, proustite, enargite, bournonite, boulangerite, jamesonite, and plagionite. Sulphides whose metallic conductivity led to featureless, almost total, absorption of infra-red radiation included chalcosine, troilite, millerite, covelline, bornite, and pyrrhotine: only the spectrum of the last is illustrated as a typical example.
Comparison of the spectra reproduced here with those previously published show a fair measure of agreement, although there are discrepancies. Povarennykh and co-workers, for example, have reported a common sequence of broad absorption bands at 370, 280, and 180 cm−1 for minerals that were found here to exhibit featureless metal-like absorption. The sources of these and other discrepancies are briefly discussed.