No abstract

Halloysite has fascinated investigators ever since it was first discovered that, in obvious contrast to the other kaolin subgroup minerals, namely kaolinite, dickite and nacrite which occur primarily in planar platy or blocky forms, many halloysites adopt an unusual tubular morphology. Spheroidal halloysite is also very well documented especially from soils, but here our focus will be entirely on the tubular form of halloysite, increasingly referred to as halloysite nanotubes or HNTs due to a rapidly expanding range of applications in a wide variety of technologies. Aside from its unusual morphologies, halloysite is also distinct amongst the other kaolin polytypes in that it is hydrated with H2O molecules positioned in the interlayer space between the fundamental 1:1 layer combination of tetrahedral and octahedral sheets that form the basic kaolin structure.Indeed, according to Churchman & Carr (1975) the single most important characteristic that identifies, defines, and distinguishes halloysite as a distinct kaolin mineral is the presence, or evidence of the former presence, of molecules of H2O in the interlayer space. Interlayer H2O in halloysite is exceedingly labile and in response to changing environmental conditions, both naturally in the field or subsequently in the laboratory, it is readily and irreversibly lost. In its fully hydrated state halloysite contains two interlayer H2O molecules accounting for 12.25 wt. % of the molecular formula unit which can be written as Al2Si2O5(OH)4·2H2O. With this full complement of interlayer H2O halloysite has a primary basal spacing, as observed in X-ray diffraction (XRD) patterns, of approximately 10Å. Because the loss of the interlayer H2O is generally not a 3 Published in Clay Minerals V 51,

The present work focuses on the subalpine range of the Italian Alps to determine the influence of aspect and consequently climate on soil humus properties and chemistry. This was done by comparing soils developing in north-and south-facing sites on siliceous parent material. The soils were investigated with respect to the total organic C and N content, C and N contents of organic matter (OM) density fractions and of labile(oxidised by H2O2) and stable (H2O2-resistant) fractions. Further characterisation of OM and the different fractions was performed with Diffuse Reflection Infrared Fourier Transform (DRIFT), Scanning Electron Microscopy/Electron Diffuse Scattering (SEM/EDS) and radiocarbon dating. The soils at north-facing slopes had a higher OM content. Density measurements and the H2O2 fractionation proved that this higher content was primarily due to a more pronounced accumulation of weakly degraded, labile organic materials when compared to the south-facing slopes. Independent of the sites, a large part of OM (around 50% of OM) was fixed in the densest fraction (N2 g/cm3) which correlated well with the abundance of the H2O2-resistant fraction. The 14C ages of the latter were up to 17,000 years, reflecting the presence of stable, refractory OM and the effectiveness of organo-mineral interactions in protecting OM from decay. Podzolisation has been more intense at north-facing sites. Due to the accumulation of weakly degraded OM, eluviation of Fe and Al is strongly enhanced. High-mountain ecosystems like the Alps are very sensitive to changing environmental conditions such as global warming. Especially at cooler sites, the obtained results suggest that a warmer climate, and thus more favourable conditions for biological activity, will lead in the short-to mid-term to an increased loss of accumulated, weakly degraded OM . 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 and thus more favourable conditions for biological activity, will lead in the short-to mid-term 21to an increased loss of accumulated, weakly degraded OM. 22 23

No abstract

The function of human geophagy has long been questioned. We sought to test hypotheses concerning its potential physiological effects through analysis of soils and patterns in geophagy behavior. Eleven samples of geophagic soils consumed by pregnant women on Pemba Island, Zanzibar, Tanzania, were characterized according to their color, texture, major element chemistry, trace element chemistry, bulk mineralogy, and clay mineralogy. An epidemiological study (N = 2367) and ethnographic interviews (N = 57) on Pemba yielded information about geophagic behaviors and socio-demographic and biological characteristics of those who consumed earth. The soils varied widely in color, ranging from light red to white through various shades of brown and yellow, and texture ranged from clay to sand. Major element chemistry of the soils also varied greatly; most were low in Fe and Ca. Trace elements, whether of biological or non-biological significance, were uniformly low when compared with normal ranges of mineral soils. The sole commonality among the samples is that all clay fractions were dominated by a kaolin mineral: kaolinite, halloysite, or a mixture of both. Geophagy behavior also varied greatly, with one major exception: a greater proportion of pregnant women (7.1%) and young children (4.5%) consumed earth than non-pregnant women (0.2%) or men (0%). The presence of kaolin mineral in all samples, its palliative and detoxifying properties, and the highest prevalence of geophagy among those most biologically vulnerable suggest that geophagy may be a protective behavior.