Abstract

Near infrared (NIR) spectroscopy is a technique that can be utilised to analyse minerals remotely through a fibre-optic cable. A suite of sulphate efflorescent minerals from the El Jaroso ravine, Sierra Almagrera, Spain have been analysed by ultraviolet, visible, NIR and mid infrared (IR) spectroscopy. Such a suite of minerals may be used to model the types of mineral deposits on Mars. The minerals were analysed by scanning electron microscopy and X-ray microanalysis (EDX) before spectroscopic analysis. Halotrichite was observed and the EDX analyses showed the mineral to be a mixture of heinrichite and pickingerite. The NIR spectrum of the eflorescencia sample showed the sulphate deposit to be composed of a mixture of jarosite and halotrichites. The 7400 to 6400 cm⁻¹ (1351 to 1562 nm) NIR spectral region of the efflorescent sulphate minerals can be used to characterise the various sulphate deposits. The detection of a band at 8338 cm⁻¹ (1199 nm) reveals the presence of ferrous iron in jarosite which is unusual for the jarosite minerals. This can be caused by ferric iron reduction by thermophilic iron-oxidising bacteria. Mid IR spectra showed the characteristic OH stretching bands of the jarosites and the efflorescent mixtures. The position of water stretching vibrations at 2900 cm⁻¹ and lower shows strong hydrogen bonding as is also evidenced by water bending modes at around 1682 cm⁻¹.

© 2006 NIR Publications

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