%0 Journal Article
%A Santiago Buey, Cristina de
%A Súarez Barrios, Mercedes
%A García Romero, Emilia
%A Doval, Mercedes
%T Mg-Rich smectite "precursor" phase in the Tagus basin, Spain
%D 2000
%@ 0009-8604
%U https://hdl.handle.net/20.500.14352/57106
%X The pink clays from the Tagus basin, Spain, were characterized by X-ray difraction (XRD),infrared spectroscopy (IR), scanning electron microscopy (SEM), and transmission electron microscopy(TEM). Chemical data were obtained by plasma emission spectroscopy and analytical electron microscopy(AEM), and specific surface and cation-exchange capacity were measured also. The data indicate thatthese pink clays are primarily stevensite. This Mg-rich smectite is characterized by poor crystallinity, ahigh degree of structural disorder, trioctahedral character (pure magnesian), a very low cation-exchangecapacity, a very small crystal size (which generates an abnormally high specific surface area), and adeficiency of octahedral cations. On the basis of the very small crystal size, a large number of edgedislocations, the lack of periodicity (turbostratic) in the structure, and a cellular (spherical) texture observedby TEM, we consider this occurrence to be an early stage of crystallization. Unlike other precursorclay materials described in the literature, this clay is not an alteration of volcanic ash, but it was generatedby precipitation from a Si- and Mg-saturated medium.
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