FE-57 MOSSBAUER INVESTIGATION OF NATURALLY PURE ALPHA-FEOOH FROM THE SUKINDA OCHRE

The X-ray powder diffraction (XRD) and Mossbauer spectroscopic investigations indicate that the brown ochre from Sukinda (India) is composed solely of alpha-FeOOH (goethite). The mean crystalline diameter parallel to (111) is 12.8 nm. The 'ultrafine' particles cause a superparamagnetic (SPM) relaxation effect as observed in room temperature Mossbauer spectrum. The substitutional effects of Al3+ and Si4+ for Fe3+ in SPM relaxation may be considered negligible as it contains low Al2O3 (0.22%) and SiO2 (0.76%). The H2O content (16.56 wt%) is possibly due to bonded hydroxyl groups manifested by a broad infrared band in the region 2800 to 3600 cm-1. This unusually pure goethite is presumed to be the ultimate product of iddingsitisation during the hydrothermal transformation of olivine of the Dunite rock.