Secondary ferrimagnetic minerals in Welsh soils: a comparison of mineral magnetic detection methods and implications for mineral formation

Abstract

A range of low-temperature and isothermal magnetic measurements are used to identify the secondary ferrimagnetic mineral (SFM) grain sizes in 10 representative soil samples from Wales. A comparison of percentage frequency-dependent susceptibility ( zFD percentage) and low-temperature remanence measurements shows that they are sensitive to different ranges of superparamagnetic (SP) grains. The relative distributions of SP grains and stable single domain (SSD) grains are similar in nine of the samples. Typical distributions for soils dominated by SFMs are %20-30 per cent SSD and 70-80 per cent SP. Multidomain (MD) grains were not detected in the samples studied. There is evidence that some soils contain significant numbers of ultrafine SP grains <0.010 pm that are not detected by low-temperature remanence measurements at 20 K and which will have the effect of depressing values of low-field susceptibility (xLF) and zFD percentage. A mixing model suggests that zFD percentage may be used semiquantitatively to estimate the proportion of SP grains in a sample. The positively skewed grain-size distributions strongly suggest a mechanism of SFM formation that is driven by processes at the m scale, thus supporting weathering and fermentation as controlling processes, rather than the degradation of SSD bacterial magnetosomes and primary minerals.

Granulometric and magnetic properties of deposited particles in the Beijing subway and the implications for air quality management

“…The χ fd % versus χ ARM /SIRM plot (Fig. 5) (Dearing et al, 1997), shows the subway particulate matters are dominated by multi-domain (MD, 10-100 μm for magnetite) and pseudo-single domain (PSD, 1-10 μm for magnetite) particles. The plot also confirms that the magnetic particles in the subway system are finer than the urban particles.…”

Magnetic Susceptibility of Soils from Eastern Botswana: A Reconnaissance Survey and Potential Applications

“…Frequency-dependent susceptibility (χfd) can indicate the presence of grains lying at the stable single domain-super-paramagnetic (SSD-SP) boundary, around 0.02 μm for isodiametric grains (Mullins, 1977;Dearing et al, 1996a;Worm, 1998;Dearing, 1999;Lu et al, 2008). Relatively high χfd% indicates the concentration of SP grains in soil, and if it is less than 4%, MD (multi-domain) and PSD (pseudo single domain) or SSD grains dominate (Dearing et al, 1996a(Dearing et al, , 1997Evans and Heller, 2003;Hu et al, 2007). Further, χfd% is correlated with the age and or the degree of soil weathering (Singer et al, 1996;van Dam et al, 2005), and can also be used to estimate the viscous remanent magnetization of the samples.…”

“…Frequency dependent susceptibility is used to detect ultra-fine (<0.03μm) super-paramagnetic (SP) minerals occurring as crystals produced by bacteria or by chemical processes in the soil (Dearing et al, 1996a(Dearing et al, , 1997Dearing, 1999;Muxworthy, 2001;Maher et al, 2003). In this study, the procedure involved measuring volume magnetic susceptibility at 0.46 kHz (χlf) and 4.6 kHz (χhf).…”

Spectroscopic and ancient geomagnetic field intensity studies on archaeological pottery samples, India

“…All the samples show χ FD % > 2 but most of the samples fall in between 4-10% suggesting the presence of significant amount of the superparamagnetic magnetite grains. Jordanova [9] has reported that burnt clay samples with χ FD % values of 6-10% contain significant content of fine superparamagnetic magnetite grains of sizes 0.012-0.023 µm [22]. The investigator's results suggest that the pottery samples under investigation are magnetically enhanced materials in terms of concentration and degree of crystallinity of magnetite.…”