Crystallization of hematite and goethite in the presence of soil minerals

Freshly precipitated ferrihydrite, 5Fe (sub 2) O (sub 3) .9H (sub 2) O, was stored at pH 7 and 40 degrees C alone and in the presence of muscovite, kaolinite, quartz, gibbsite and soil clay at varying Mg mineral per mole Fe ratios (20, 200 and 500), and the crystallization of ferrihydrite into hematite and goethite was monitored after 20, 50, 100, 148 and 210 days. After 210 days the ferrihydrite suspension of soil minerals was nearly completely converted into a mixture of goethite and hematite. Muscovite seems to promote the transformation but deferrated soil clay > kaolinite > gibbsite > quartz retard the formation of the oxides. The best- developed morphologies of hematite plates, also with 120 degrees oriented goethite needles, were observed in the presence of muscovite, suggesting a strong template effect.