Beidelit osadów serii poznańskiej

Andrzej Wiewióra, Ryszard Wyrwicki




The sediments of the Poznań Series are wide-spread and they have a considerable practical value. However their mineral composition still remains obscure. The authors decided to study the mineral composition of the clayey fractions of the sediments and the crystallochemical properties of the major rock-forming mineral.

For this purpose the clayey fraction of the youngest sedimentation cycle from Mastki has been chosen.

X-ray analysis shows that this fraction contains 12 per cent of kaolinite and 5 per cent of quartz. The chemical compositions of these minerals were subtracted from the chemical composition of the clayey fraction. The chemical composition of beidellite obtained in this way was finally recalculated to the following crystallochemical formula:

(Ca0.14 Mg0.02 K0.12 Na0.03) [(Al1.29 Fe3+0.18 Mg0.18 Ti0.18 Fe2+0.02 (Si 3.61 Al0.39) O10 (OH)2]×1.05 H20

This shows that the charge of the layer is contained within limits which are characteristic of beidellite. The great majority of isamorphic substitutians are concentrated in the tetrahedral layer. This is reflected in the thermal properties of the mineral, its low temperature of dehydraxylation (560°C), and – what it typical of beidellite – its continuing capacity far swelling after U. Haffman's and R. Klemen's test (1950) and after R. Green-Kelly's test (1953). C. E. Weaver's test (1958) did not show any considerable capacity for potassium fixation and this excludes the possibility that the beidellite examined here might have originated from degradation of micas.


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