Topic
Vermiculite
About: Vermiculite is a research topic. Over the lifetime, 2320 publications have been published within this topic receiving 37142 citations.
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TL;DR: In this article, an aeolian, periglacial sand dune formed in northeastern Indiana about 13,000 b.p. has been weathered to vermiculite.
Abstract: Weathering has etched and deeply-denticulated the constituent orthopyroxenes, and chlorite has been transformed to vermiculite in the upper 3 m of an aeolian, periglacial sand dune formed in northeastern Indiana about 13,000 b.p. Pyroxene weathering begins with the development of cleavage-parallel etch pits on {010} and {100} surfaces. These pits coalesce and eventually crop out on basal surfaces as denticulations. The mean denticulation size increases logarithmically toward the surface, and the denticulation size of the orthopyroxenes is a quantifiable feature of the weathering process. Ferruginous pendants, microboxworks of iron oxides, and other indications of iron redeposition within the ortho-pyroxene microenvironments were not observed. Chlorite in the dune has been weathered to vermiculite. The parent chlorite is a high-Fe variety, and the transformation to vermiculate does not involve the development of a chlorite/vermiculite intermediary phase. Fe2+ is oxidized as part of the transformation process and this iron is retained in the sediment as discrete goethite and as crystalline and noncrystalline coatings on the dune grains. The vermiculite from depths shallower than 64 cm is only partly expandable and is completely collapsed by K-saturation or heat treatment. This is a hydroxy-Al vermiculite and its formation is typical of intense weathering under the acid conditions prevalent at the dune surface.
15 citations
01 Jan 2007
15 citations
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TL;DR: In this paper, the local structure of interlayer lanthanide ions exchanged into vermiculite clay has been determined as a function of the nature of the ion and the physical form of the sample (powders and oriented films) using X-ray absorption spectroscopy.
Abstract: The local structure of interlayer lanthanide ions ion-exchanged into vermiculite clay has been determined as a function of the nature of the lanthanide ion and of the physical form of the sample (powders and oriented films) using X-ray absorption spectroscopy. Water molecules form the first coordination shell, with metal–oxygen bond lengths of 2.52 (La—O), 2.53 (Ce—O), 2.32 (Er—O) and 2.33 A(Lu—O), very similar to the corresponding interatomic distances in aqueous lanthanide nitrate solutions. However, the coordination numbers of the heavier lanthanide ions are greater than those of the lighter ones, in contrast to the behaviour observed in solution. This variation is attributed to the participation of coordinated water in the transmission of local charges on the lanthanide ions to the vermiculite layer surface. Across the lanthanide series a significant difference in coordination number between La-vermiculite powder (6 neighbours) and film (9 neighbours), is reduced in the cerium sample (7.5 and 9, respectively) and reached a negligible variation in the heavier (Er, Lu) vermiculites. This is attributed to a diffusion phenomenon of water within the vermiculite interlayers. Preliminary a.c. conductivity measurements of Lu-vermiculite films are in the range of 10–6 S cm–1.
15 citations