# Microstructural Characterization of the Mn Lepidolite Distribution in Dark Red Clay Soils
## 3 Results
### Mineral Distribution Assessment
The separation process facilitates the dispersion of the finest particles while the coarser fraction settles to the bottom of the vial. Figure 6d reveals the complete removal of all fractions larger than 10 \(\upmu\)m. The remaining finest particles consist mainly of a lepidolite and kaolinite mixture, with traces of quartz particles measuring approximately 5-10 \(\upmu\)m. The smaller goethite particles remain mixed up with the finest clay particles. Sample B has a clayey texture very abundant in lepidolite and kaolinite fine particles with sizes predominantly about 1 \(\upmu\)m (only a few being about 5-10 \(\upmu\)m) that tightly surrounds the coarser fractions composed of quartz boulder-like particles and goethite, Figure 6b. During the separation process, the coarser sandy fractions settle at the bottom of the vial while the clay mixture remains suspended. The obtained powder contains only the finest fractions dominated by lepidolite with moderate traces of kaolinite and small quartz particles, Figure 6e. The washing separation process enriches the filtered sample in lepidolite fine particles organized in small microstructural clusters of about 3-15 \(\upmu\)m. They have an intense and uniform red-orange color generated by the random disposal of the  
Figure 6: MOM images of the initial soils: (**a**) Sample A, (**b**) Sample B, and (**c**) Sample C and for the extracted fine fractions: (**d**) Sample A, (**e**) Sample B, and (**f**) Sample C.  
finest particles of lepidolite, giving a clue about their nanostructural organization (fact in good agreement with the XRD peaks broadening). Sample C displays a dense kaolinite clay matrix closely enveloping the quartz particles, which have a boulder-like aspect and sizes of about 5-75 \(\upmu\)m (smaller than observed in the sandy Sample A). The kaolinite aggregates have a yellow nuance caused by their random orientation of the finest particles, Figure 6c. Some of these aggregates turn brown because of the goethite amount. The brown color intercalation with kaolinite yellow indicates a refined microstructural distribution of the iron hydroxide particles, which features only a few grainy particles up to 15 \(\upmu\)m in diameter. The washing separation process successfully removes coarse particles, including quartz and goethite, from the aqueous dispersion. The resulting fine powder is primarily composed of kaolinite stained with goethite, as clearly indicated by the yellow clusters with brown spots shown in Figure 6f. Both lepidolite and kaolinite form a foggy embedding matrix of the coarser mineral particles, as observed by MOM images in Figure 6, which are well separated through the separation process. It corresponds to the broadened aspect of the lepidolite and kaolinite diffraction peaks in Figure 3b, indicating nanostructural organization. The crystallite size can be calculated using the Scherrer formula [43]. It was applied to the XRD patterns in Figure 3b, and the obtained values are displayed in Table 3.  
The organization of lepidolite and kaolinite fine particles into small microstructural clusters of approximately 1-2 \(\upmu\)m, as observed after the washing separation process, along with the nanoscale size of their crystallites, suggests the potential presence of a significant quantity of clay nanoparticles. This fact requires advanced ultra-structural investigation, which will be properly assessed by atomic force microscopy in subchapter 3.4.