A Raman spectroscopic study of synthetic giniite

The mineral giniite has been synthesised and characterised by XRD, SEM and Raman and infrared spectroscopy. SEM images of the olive-green gimite display a very unusual image of pseudo-spheres with roughened surfaces of around 1-10 mu m 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 3100cm(-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(-1) are attributed to the FeO stretching vibrations. The ginfite 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 (v2) bending modes suggesting a reduction of symmetry of the (PO4)(3-) units. (c) 2006 Elsevier B.V. All rights reserved.