Near-infrared and mid-IR spectroscopy of selected humite minerals

Abstract

Spectral reflectance properties of a number of iron-bearing humite minerals have been examined to draw quantitative relationships between composition, structure, and reflectance spectra. The measured knowledge yields information on the geologic history of surface minerals on Mars through the identification of types, abundance, and composition of iron-bearing silicate minerals. A prominent feature in the spectra of humite minerals is a complex band system in the NIR that arises in the range 11250-7850 cm À1 due to Fe 2+ . The broad band profile resolved into four bands are assigned to dd-transitions of Fe 2+ (M1 6 ), bands around 10,200 and 9000 cm À1 , and of Fe 2+ (M2 6 ), bands centred at 9800 and 9400 cm À1 . The fundamental overtones of OH-stretching modes are observed in the range 7400-7100 cm À1 . The sharp band centered around 5075 cm À1 with extended bands on either side of 5200-4810 cm À1 is characteristic of OH-and Si-OH combination modes. The complexity of OH spectrum increases with number of silicate layers in humites. Infrared spectroscopy is able to differentiate the mineral group into two-, three-or four-layered silicates by the main OH band observed at 3573, 3568, 3564 and 3563 cm À1 for chondrodite(1), chondrodite(2), humite and clinohumite. An anomaly for Ti-clinohumite is observed at 3557 cm À1 which is accounted for by the presence of titanium. #

Kumtyubeite Ca5(SiO4)2F2--A new calcium mineral of the humite group from Northern Caucasus, Kabardino-Balkaria, Russia

“…the powder data are given below: monoclinic, space group: P2 1 /a, a = 11.454(2), b = 5.056(1), c = 8.857(1) Å, β = 108.84(1)°, V = 485.51(2) Å 3 , Z = 2. FTIR and Raman spectra of kumtyubeite resemble spectra of humite-group minerals (Prasad and Sarma 2004;Frost et al 2007aFrost et al , 2007b. The FTIR spectrum of kumtyubeite shows the following bands (main bands are italic): 427,507,530,561,638,656,722,760,779,822,837,865,904,934,957,993,1113,1165,3541,3551, and 3558 cm -1 (Fig.…”

“…3) strongly resemble each other. FTIR and Raman bands measured for the reinhardbraunsite-kumtyubeite series may be divided into four groups following Frost et al (2007aFrost et al ( , 2007b: group 1 = modes lower than 400 cm -1 corresponding to the vibrations of CaO 6 octahedra; group 2 = modes 400-700 cm -1 are related to bending vibrations of SiO 4 tetrahedra; group 3 = modes 700-1000 cm -1 are related to the stretching vibrations of SiO 4 ; and group 4 = modes between 3480 and 3562 cm -1 are characteristic of (OH)-group vibrations.…”

Synthesis and vibrational spectroscopy of halotrichite and bilinite

“…However, as it has been shown by different techniques and spectral regions discussed, halotrichite is the predominate phase that forms. Higher wavenumber bands (1200-1100 cm −1 ) are observed for both bilinite and halotrichite and are assigned to 3 (SO 4 2− ).…”

“…Halotrichite observed bands at 2491 and 2294 cm −1 , whilst these bands are absent for bilinite. 4 2− stretching region 1200-800 cm −1…”

“…Electronic bands of transition metals 12,500-7500 cm −1 This spectral region includes electronic bands resulting from transition metal ions in the structure and also bands related to the second fundamental overtones of the OH stretching vibrations [4][5][6][7][8][9][10][11]. The NIR spectra of halotrichite and bilinite in this spectral region are provided in Fig.…”