Tuffite-derived magnetic soils in the Alto Paranaíba region, State of Minas Gerais, Brazil, have a variable mineralogy and are assumed to contain iron oxides that are isoestructural to spinel, more specifically, (Mg,Ti)-rich magnetite and maghemite. In this study, magnetic portions (saturation magnetization, 34.4 < s/J T-1 kg-1 < 43.7) were separated from sand fractions of pedomaterials of a Brunizem (Chernosol) (samples labeled AP31CR; AP31B and AP31A) and of a leptic Chernosol (AP33CR e AP33A) developed from tuffite were collected near the city of Patos de Minas, […]

The iron oxide mineralogy of sand, silt and clay fractions was studied in five soil materials. Samples were collected from a pedon of a Red Nitossolo (Brazilian Soil Classification; related to an Alfisol in US Soil Taxonomy) developing on a tholeiitic basalt, near the town Tupaciguara (18 o 35 ‘ 33 ” S; 48 o 42 ‘ 18 ” W) in the region of Triângulo Mineiro, state of Minas Gerais, Brazil. Portions of sand and silt were analyzed by magnetic separation and selective chemical treatments with NaOH […]

Maghemite (γFe2O3) from tuffite is exceptionally rich in Mg, relatively to most of those reportedly found in other mafic lithosystems. To investigate in detail the compositional and structural variabilities of this natural magnetic iron oxide, sets of crystals were isolated from samples collected at different positions in a tuffite weathering mantle. These sets of crystal were individually powdered and studied by X-ray diffractometry, Mössbauer spectroscopy, magnetization measurements and chemical analysis. Lattice parameter of the cubic cell (a0) was found to […]