Intérêt géochimique et signification minéralogique du paramètre moléculaire Ki = SiO2/A12O3 dans l'étude des latérites et bauxites

The author first reviews the various analytical conditions which must be fulfilled if a significant value for the synthetic parameter Ki=SiO2/A12O3 to be obtained, and then approaches the problem of the mineralogical interpretation of results. It is indicated that a value of Ki< 2 does not necessarily show the presence of aluminium hydrates, because of the existence on the surface of the globe of phyllitic silicates or amorphous constituants (allophanes) richer in alumina than kaoli -nite itself. However, in materials characterised by the association kaolinite -aluminium hydroxides (lateritic and bauxitic earths) the determination of the Ki relationship is useful for the estimation of the amount of free alumina and the determination of the quantitative minerological composition (kaolinite, gibbsite, boehmite . . . )