Sulphate efflorescent minerals from the El Jaroso ravine, Sierra Almagrera, Spain—a scanning electron microscopic and infrared spectroscopic study. An Abstract from Journal of Near Infrared Spectroscopy

Ray L. Frost,^a Daria L. Wain,^a B. Jagannadha Reddy,^a Wayde Martens,^a Jesus Martinez-Frias^b.c and Fernando Rull^b,c
^aInorganic Materials Research Program, School of Physical and Chemical Sciences, Queensland University of Technology, GPO Box 2434, Brisbane Queensland 4001, Australia. E-mail: r.frost@qut.edu.au
^bCentro de Astrobiología, INTA-CSIC, Associated to the NASA Astrobiology Institute, Ctra de Ajalvir km. 4, 28850 Torrejon de Ardoz, Madrid, Spain. E-mail: martinezfrias@mncn.csic.es
^cCristalografia y Mineralogia, Unidad Asociada al Centro de Astrobiologia INTA-CSIC, Universidad de Valladolid, 47006 Valladolid, Spain. E-mail: rull@fmac.uva.es

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.