Mineralogy, petrography and structures of iron crusts (ferricretes) developed on sandstones in the western part of Senegal

Abstract

In the Ndias Massif (western Senegal), the detailed study of ferricrete profiles developed on kaolinic sandstones shows that these ferricretes (iron crusts) are composed of a succession of different horizons or layers, the arrangement of which is both chronologic and genetic. The most evolved, nodular facies develop at the tops of profiles and on lower slopes, and they originate from the least evolved, massive facies. Even as these facies follow one another, so does a succession of goethite, Al-hematites with 6—13% moles of Al 2O 3 and AI-goethites with 16–22% moles of AlO(OH).