Abstract: Diffractograms of lepidocrocites formed from the oxidation of Fe(II) chloride solutions at pH 7 and 25°C showed differential line broadening with (0k0) reflections being much sharper than (hk0) or (hkl). As the initial [Cl]/[Fe] ratio was increased from 2, crystallinity increased in all axial directions, as defined by the width at half height of diffraction peaks. At [Cl]/[Fe] ratios greater than ∼8, the crystallinity did not increase further, and for reflections involving the a-axis direction, it appeared to decrease. Increased [Cl]/[Fe] ratios changed the rate of the oxidation/hydrolysis reactions. These variations reflect changes in the stability and/or composition of the intermediate green rust phase, (Fe(II)Fe(III) hydroxychloride) in the high [Cl] environment. The influence of the [Cl]/[Fe] ratio was related to the experimental conditions employed, especially where they influenced the rate of oxidation.