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/npsi/ctrl?lang=en http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?lang=fr Access and use of this website and the material on it are subject to the Terms and Conditions set forth at http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/jsp/nparc_cp.jsp?lang=en NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur.Engineering Geology, 4, 2, pp. 133-153, 1970-07-01 Fabric of leda clay investigated by optical, electron-optical, and x-ray diffraction methods Gillott, J. E. Fabric, palaeosalinity and engineering data are given for five samples of Leda clay. It is shown that the layer structure silicates in two of the samples are oriented parallel to the bedding; that in the other three samples the platy minerals have a near random arrangement. X-ray diffraction studies showed that there was no difference in the orientation of 7A and 10A layer structure silicates.Palaeosalinity values deduced from boron content indicate that three of the samples were deposited in water that was fresher than normal marine. The other two samples were deposited in a nearly normal marine environment. The correlation between fabric and palaeosalinity data is fairly good, though information on a larger number of samples is needed before the method can be satisfactorily evaluated for Leda clay.Moisture removal by four different methods shows that original fabric can be affected by the technique of sample preparation.The evidence is in agreement with the idea that fabric was Inore affected by conditions at the time of deposition than by subsequent events.

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Certain fine-grained argillaceous dolomitic limestones show an increase in solid volume when placed in strong alkali. Mineralogical analysis shows that the dolomite is replaced by magnesium hydroxide (brucite), calcium carbonate, and alkali carbonate. This reaction does not account directly for the expansion, as the volume of the solid products is less than the volume of the dolomite.Expansion is shown to be the result of an increase in solid volume that results from water uptake. The behavior is accounted for by a hypothesis that may be summarized as follows.(1) Alkaline attack on the dolomite crystals releases included clay in an "active" state with an unwetted surface.(2) Some of the Ca++ and Mg++ ions probably present on exchange sites are replaced by Na+ ions.(3) Development of a hydrated double layer made up of oriented water molecules, cations near the newly exposed clay surface, and anions further from the surface.(4) Development of the double layer and accompanying hydration processes cause the water uptake, which leads to expansion.