Multiple Iron-Rich Spinel Phases and Hematite in a Magnetic Soil Developing on Tuffite

Compositional and structural variabilities of Mg-rich iron oxide spinels from tuffite

“…The relative amount of Ti 4+ increases in the same direction. The formula (6) is comparable to the core phase composition (9) reported by Goulart et al (1997), for a spinel grain from a soil derived from tuffite of the same area, in which all iron content was allocated in its higher oxidation state (the numbers in brackets following the formula indexes were originally estimated uncertainties over the last significant digit, taken as standard deviations from the mean of corresponding probed points):…”

“…In one group, with higher unit cell-dimensions, a 0 ranges from 0.8397 nm up to 0.8412 nm; in the other, a 0 ranges from 0.834 nm up to 0.838 nm. Actually, the reported lattice parameter a 0 = 0.8417 nm for the Fe 2+ -containing soil iron-spinel from Goulart et al (1997) is significantly higher than the characteristic a 0 = 0.8380(2) nm of the fully oxidized (Mg, Ti)-rich maghemite (Fabris et al, 1995) from the parent tuffite. A further study by Fabris et al (1997) on a set of crystals of the iron-spinel from this tuffite revealed an Fe 2+ content of up to 13 mass %.…”

“…It was later suggested that structural iron in the inner phase of some grains of iron rich spinel from tuffite had a ferrous character . Whether the structural heterogeneity of such iron oxide spinels is of a wider spatial occurrence than that reported in single-sample studies Goulart et al, 1997) in that system was no clear at that time.…”

“…Goulart et al (1997) have shown evidences of multiple spinel phases in a soil developing on tuffite of that same area, with different chemical compositions and unit cell dimensions determined from the (440)-reflection. One of these phases had a similar composition to the (Mg, Ti)-rich maghemite described by Fabris et al (1995).…”

Mössbauer, X-ray and Magnetic Studies of Black Sand from the Italian Mediterranean Sea

“…Several studies have been published on Mössbauer spectroscopy of volcanic soils (see for ex. [4][5][6][7]). Mössbauer spectra have been intensively studied for many iron rich minerals and reference data are available.…”