Mineralogy of poorly crystalline aluminium phases in the B horizon of Podzols in southern Sweden

Poorly crystalline Al components of the clay fraction are often neglected in soil mineralogical studies. In this study 7 B horizons from podzolised soils in Sweden were analysed using a combination of infrared (IR) spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and selective extractions. It was found that most Bhs and Bs horizons contained allophane, imogolite and more or less hydroxy-interlayered vermiculite. Some Bhs and Bs horizons also contained small amounts of kaolinite and/or gibbsite. In one acid Bh horizon organically complexed Al was the only reactive Al fraction of importance. The vertical patterns of vermiculite and allophane/imogolite suggested that both had formed during the podzolisation process, but due to different mechanisms. The pattern of kaolinite and gibbsite occurrences indicated that these minerals were mostly inherited from the parent material. Oxalate and pyrophosphate extractions suggested that allophane and imogolite constituted the most important reactive inorganic Al fraction in the soils. This shows that allophane and imogolite seem to be the typical, rather than the occasional, reactive inorganic Al phases that form in the B horizon as a result of podzolisation.