On-line version ISSN 1678-4596
SOUZA JUNIOR, Ivan Granemann de; COSTA, Antonio Carlos Saraiva da; VILAR, Cesar Crispim and HOEPERS, Allan. Mineralogy and magnetic susceptibility of iron oxides of B horizon of Paraná state soils. Cienc. Rural [online]. 2010, vol.40, n.3, pp.513-519. ISSN 1678-4596. http://dx.doi.org/10.1590/S0103-84782010000300003.
Highly weathered tropical soils tend to accumulate iron and aluminum oxy-hydroxides. Among the iron oxy-hydroxides found in the clay fraction, goethite (Gt) and hematite (Hm) are the most abundant and studied. A smaller number of investigations have been publish to identify and to quantify maghemite (Mh), a ferrimagnetic mineral present in the clay size fraction of the soils, mainly in those developed from mafic rocks. Maghemite, along with magnetite (Mt) is responsible for the spontaneous magnetic behavior of the soils. This mineralogical attribute can be easy measured, in soils and sediments by mass magnetic susceptibility (χLF), which magnitude is proportional to the concentration of ferrimagnetic minerals and it has been object of studies worldwide. The purpose of this research was to identify and quantify, by χLF, the ferrimagnetic minerals of 32 samples from B-horizons of Paraná state soils. The mineral species present in the iron oxides concentrated clay size fractions were identified and semiquantified by x-rays diffraction (XRD). In this fraction the most abundant minerals are Gt and Hm. Maghemite was detected in 31 samples by χLF and in only 17 samples by XRD. The χLF values ranged from 16 to 8.077x10-8m3 kg-1 in the fine earth; from 12 to 7.953x10-8m3 kg-1 in clay fraction and from 0 to 18.737x10-8m3 kg-1 in clay fraction, after concentration of the iron oxides. The Mh of the soils presented an average value of 62.728x10-8m3 kg-1 and their presence in the X-rays diffractograms was only observed in samples with χLF values above 1.000x10-8m3 kg-1.
Keywords : clay fraction; ferrimagnetic minerals; XRD.