01658naa a2200241 a 450000100080000000500110000800800410001910000180006024501970007826000090027552008870028465000130117165000090118465000090119365300230120265300210122565300280124670000180127470000180129270000160131070000160132677300740134217844291995-06-08       1978    bl ---       0--  u    #d1 aBIGHAM, J. M.  aIron oxide mineralogy of well-drained ultisols and oxisolsbI. Characterization of iron oxides in soils clays by Mossbauer spectroscopy, X-ray diffractometry, and selected chemical techniques.  c1978  aThe iron oxides in subsoil clays (&lt0.2 um) from five North Carolina Ultisols and two Brazilian Oxisols were analyzed by Mossbauer spectroscopy, X-ray diffractometry, and selected chemical techniques. Goethite and hematite were identified as the dominant crystalline iron oxides in these clays. Partial substitution of AI(III) or other nonmagnetic ions for Fe(III) in the oxide structures caused reduced unit cell dimensions and subnormal effective internal magnetic fields. All samples exhibited strong superparamagnetic relaxatgion, a collapse of the Mossbauer magnetic splitting at ambient temperatures due to the ultrafine size of the oxide particles. Neglible amounts of iron were solubilized with acid ammonium oxalate; however, the Ultisol clays did contain significant amounts of silicate and/or interlayer iron that was not extractable with dithionite-citrate-bicarbonate.  ahematite  asoil  aSolo  aAluminous goethite  aMossbauer effect  aNuclear gamma resonance1 aGOLDEN, D. C.1 aBOWENS, L. H.1 aBUOL, S. W.1 aWEED, S. B.  tSoil Science Society of American Journalgv.42, n.5, p.816-824, 1978.