A Raman Spectroscopic Study of Synthetic Giniite

Abstract

The mineral giniite has been synthesised and characterised by XRD, SEM and Raman and infrared spectroscopy. SEM images of the olive green giniite display a very unusual image of pseudo-spheres with roughened surfaces of around 1 to 10 microns in size. The face to face contact of the spheres suggests that the spheres are colloidal and carry a surface charge. Raman spectroscopy proves the (PO4)3- units are reduced in symmetry and in all probability more than one type of phosphate unit is found in the structure. Raman bands at 77 K are observed at 3380 and 3186 cm-1 with an additional sharp band at 3100 cm-1. The first two bands are assigned to water stretching vibrations and the latter to an OH stretching band. Intense Raman bands observed at 396, 346 and 234 cm-1are attributed to the FeO stretching vibrations. The giniite phosphate units are characterised by two Raman bands at 1023 and 948 cm-1 assigned to symmetric stretching mode of the (PO4)3- units. A complex band is observed at 460.5 cm-1 with additional components at 486.8 and 445.7 cm-1 attributed to the ν2 bending modes suggesting a reduction of symmetry of the (PO4)3- units