Clay mineralogy in mylonite weathering products from Njimom (west Cameroon): origin and terracotta suitability

This study investigated the mineralogical assemblage of weathering products developed on mylonite rocks in west
Cameroon. Smectite and vermiculite occurrence was studied, particularly to emphasize its origin and the potential of the
samples in terracotta production. Samples characteristics were determined through X-Ray Diffraction (XRD) and X-ray
Fluorescence (XRF) methods. Weathering products were observed along road trenches of 450 m long and 50 m height
on a syenitic basement rock intruded by magmatic rock veins. Clay minerals are mainly composed of kaolinite and illite.
2:1 swelling clay minerals (vermiculite, montmorillonite) occur in some samples mainly originated from the contact
between weathering materials and quartzo feldspatic bands. The main oxides are SiO2 (46–72%), Al2O3 (16–31%), Fe2O3
(2–16%) and K2O (0.1–6%). Vermiculite may be formed by fluid-mineral interactions during alteration of the chlorite in
the plasmic microsystems of the soil. Structural changes in the upper part of the saprolite leading to the transformation
of vermiculite into smectite under supergene alteration control, which predominates in humid tropical zones. Heavy
rainfall leads to the formation of kaolinite at the expense of 2:1 clay minerals. Empirical classification revealed that the
studied weathering products can be used to produce common bricks.