Chemistry, Raman and infrared spectroscopic characterization of the phosphate mineral reddingite : (MnFe)3(PO4)2(H2O,OH)3, a mineral found in lithium-bearing pegmatite.

Abstract

Detailed investigation of an intermediate member of the reddingite–phosphoferrite series, using infrared and Raman spectroscopy, scanning electron microcopy and electron microprobe analysis, has been carried out on a homogeneous sample from a lithium-bearing pegmatite named Cigana mine, near Conselheiro Pena, Minas Gerais, Brazil. The determined formula is ðMn1:60Fe1:21Ca0:01 Mg0:01ÞP2:83ðPO4Þ2:12 ðH2O2:85F0:01ÞP2:86, indicating predominance in the reddingite member. Raman spectroscopy coupled with infrared spectroscopy supports the concept of phosphate, hydrogen phosphate and dihydrogen phosphate units in the structure of reddingite-phosphoferrite. Infrared and Raman bands attributed to water and hydroxyl stretching modes are identified. Vibrational spectroscopy adds useful information to the molecular structure of reddingite– phosphoferrite.