The use of near‐infrared spectroscopy to determine the degree of serpentinization of ultramafic rocks

Abstract

Visible and near‐infrared (0.35 to 2.5 μm) bidirectional reflection spectra were recorded for a suite of particulate samples from mineralogically well‐characterized serpenatinized ultramafic rocks. The reflection spectra typically exhibit well‐defined minima due to electronic and vibrational processes in the individual mineral constituents. The contrast of near‐infrared spectral features of primary magnesian silicate minerals and secondary hydrous‐serpentine group minerals can be used to indicate the degree of serpentinization of the rock, provided less than about 1 percent of finely divided magnetite is present. The effect of magnetite, apparent in rocks with more than 50 percent serpentine, is to reduce the overall reflectance and the contrast of spectral bands. Near‐infrared spectrometry is potentially a rapid and reliable technique for detecting the highly serpentinized rocks which constitute target areas for asbestos exploration.