Raman and Infrared Spectroscopic Characterization of the Silicate Mineral Lamprophyllite

Abstract

The mineral lamprophyllite is fundamentally a silicate based upon tetrahedral siloxane units with extensive substitution in the formula. Lamprophyllite is a complex group of sorosilicates with general chemical formula given as A₂B₄C₂Si₂O₇(X)₄, where the site A can be occupied by strontium, barium, sodium, and potassium; the B site is occupied by sodium, titanium, iron, manganese, magnesium, and calcium. The site C is mainly occupied by titanium or ferric iron and X includes the anions fluoride, hydroxyl, and oxide. Chemical composition shows a homogeneous phase, composed of Si, Na, Ti, and Fe. This complexity of formula is reflected in the complexity of both the Raman and infrared spectra. The Raman spectrum is characterized by intense bands at 918 and 940 cm⁻¹. Other intense Raman bands are found at 576, 671, and 707 cm⁻¹. These bands are assigned to the stretching and bending modes of the tetrahedral siloxane units.

Keywords:

• infrared spectroscopy
• lamprophyllite
• Raman spectroscopy
• silicate
• titanate

Acknowledgments

The authors would like to acknowledge the Center of Microscopy at the Universidade Federal de Minas Gerais (http://www.microscopia.ufmg.br) for providing the equipment and technical support for experiments involving electron microscopy.