Near- and Mid Infrared Spectroscopy of the Lithium-Bearing Amphibole Holmquistite from Barraute,Canada

Abstract

The mid- and near infrared spectra of holmquistite, a lithium-containing orthorhombic amphibole, from Barraute (Quebec, Canada) has been measured. The OH stretching region is characterised by bands around 3660, 3645, 3629 and 3613 cm⁻¹ assigned to (3Mg)–OH, (2Mg + Fe²⁺)–OH, (Mg + 2Fe²⁺)–OH and (3Fe²⁺)–OH, respectively. Based on the ratio between the 3645 and 3660 cm⁻¹ bands Fe²⁺/(Fe²⁺ + Mg²⁺) ratios in the M₁ and M₃ sites were determined to be in the range between 0.3 (mid infrared) and 0.4 (Raman). In the near infrared region, two times four bands were observed associated with the four possible combination modes of the four M–OH stretching and bending modes around 4029, 4193, 4323 and 4400 cm⁻¹ and with the four overtones of M–OH stretching modes around 7055, 7091, 7123 and 7155 cm⁻¹.