STRUCTURE TRA NSFORMA T IONS EFFECTED BY THE DEHYDRATION OF D1ASPORE, GOETHITE AND DELTA FERRIC OXIDE

X-ray powder diffraction studies have been made of the structure changes which occur on dehydrating the minerals diaspore and goethite, and also the synthetically-prepared "8-Fe203. " For diaspore and goethite the changes are interpreted in terms of superstructures referred to a hexagonal, anion lattice sub-unit which is common to both the a-type oxyhydroxides and the anhydrous corundum or hematite structures. The ferro-magnetic 8oxide, obtained by rapid oxidation of ferrous hydroxide, is showr ~ to be a true oxyhydroxide of the tbrm FeOOH. It transforms into goethite on heating at about 150 ~ but the change is incomplete due to a tendency to lose water directly to the atmosphere. An approxi-mate structure analysis has been made, using the X-ray powder data for two relatively well-crystallized ~ oxide preparations. It is concluded that the ferric ions occupy the interstices of the anion lattice in such a way that approximately 80per cent. of the iron is randomly distributed in octahedral sites, while the remainder issimilarly placed in tetrahedrat sites. This cation distribution enables both the transformation t goethite and the magnetic properties of the oxide to be satisfactorily- explained