Oxyhydroxides naturally-occurring ferric

Ferric oxyhy dr oxide minerals or phases which occur naturally are listed in Table I, and except for akaganeite, their occurrences have been described by Palache et al. (3). The oxyhydroxides found as precipitates in natural waters are usually goethite and x-ray amorphous material. Amorphous material, which comprises a relatively large proportion of most fresh precipitates, is formed under conditions of substantial supersaturation with respect to the crystalline oxyhydroxides. An amorphous phase develops by rapid hydrolysis of dissolved ferric species, particularly at pH s below 4-5 where the total concentration of such species can exceed 0.01 ppm. Amorphous material is also produced during the rapid oxidation and hydrolysis of ferrous iron-rich solutions. 

---