The structure of hydrohematite

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Abstract
Hydrohematite beside ‘weakly bound’ water removable at 160 – 200° C, contains about 3–4.5 % of tightly held H2O, the complete withdrawal of which requires a very high temperature, of about 1000°C. IR investigations have shown that this kind of water exists in the form of hydroxyl groups. For this reason it has been assumed that OH− ions occupy anion positions in the close-packed anionic sublattice of hematite together with oxygen anions and that the electrostatic neutrality is preserved by Fe3+ deficiency in the cationic positions. Accurate measurements of X-ray reflection intensities of hydrohematites revealed a decrease in intensity of all reflections due to Fe3+, and an unchanged intensity of (113)-reflection. The intensity of this reflection is exclusively dependent on anions. The results obtained agree well with the calculated values for the model assumed and fully confirm the defect character of hydrohematite structure. Thus the formula of hydrohematite should be written Fe2−x/3(OH)xO3 −x.

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