Chemistry of Mg Smectites in Lacustrine Sediments from the Vicalvaro Sepiolite Deposit, Madrid Neogene Basin (Spain)
Abstract:The chemical and structural properties of Mg smectites in the Vicálvaro sepiolite deposit have been studied in detail. The characterization was performed on different size-fractions of selected smectitic samples (5 -2 µm; 2 -1 µm; 1 -0.5 µm; <0.5 µm and <0.1 µm). The chemical compositions of individual particles (5 -1 µm) and of bulk undifferentiated fine fractions (1 -<0.1 µm) were determined by energy dispersive spectroscopy-scanning electron microscopy and interpreted with the aid of X-ray diffraction (XRD) and infrared spectroscopy (IR) methods. The XRD and IR data demonstrate that all of the Mg smectite materials studied are mainly composed of a complex mixture of stevensite, saponite and micatype minerals. Although the presence or absence of saponite cannot be confirmed absolutely, stevensite is a significant component of these Mg smectites. This is proven by the calculated layer charge reduction after the Hofmann-Klemen effect. The results are in close agreement with the suggested mechanism of topotactic overgrowth of stevensite on pre-existing phyllosilicate templates. This characterizes clay diagenesis in saline-lake systems.
Document Type: Research Article
Publication date: August 1, 2003
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