OBSERVATIONS NOUVELLES SUR LA STRUCTURE DE LA GLAUCONIE EN ACCORDEON (“VERMICULAR PELLETS”); DESCRIPTION DU PROCESSUS DE GENESE DE CES GRANULES PAR NEOFORMATION

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ABSTRACT

Since Galliher's studies on the sediments from the Monterey bay (California), vermicular pellets have been considered to be derived from mica flakes by a transformation phenomenon. Generally, it is considered that all the glauconite pellets result from the transformation of degraded smectitic- or illitic-type sheets into more ordered sheets. In the present study, it is shown that the vermicular pellets cannot be derived from the transformation of a mica flake. The mass obtained is several orders higher than the initial mass. Secondly it is noticed that the transformation process invoked do not allow for the continuing existence of the sheets. Finally, the ions of the micaceous sheet are never involved in the “transformation”, for sometimes they are found intact in the vermicular pellet. A study carried out through an electron microscope by reflexion indicates that there is crystal growth between the mica sheets. These sheets are merely a support favourable for glauconite neoformation. If the ions of the mica flake are involved in this genesis to any extent, they yield only a very low quantity of the mass of the final granule. As in the cracks of quartz grains, in feldspar cleavages or in limestone pores, the important surface constituted by the mica sheets is a catalyst for glauconite neoformation.

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