# Microstructural Characterization of the Mn Lepidolite Distribution in Dark Red Clay Soils
## 3 Results
### Mineral Distribution Assessment  
Soil samples have strong crystalline characteristics, evidenced by the diffraction peaks. Their shape is narrow, having strong intensities diffracted by the strong and densely crystallized materials; some other peaks are less intense and broadened because of the nanostructural characteristics of the finest fractions, Figure 4a. The upper soil, having a dark red color and sandy texture, is dominated by quartz, which is the most representative mineral in this sample. It features narrow peaks with strong intensities. It is followed by a clay mixture composed of kaolinite and lepidolite. Kaolinite peaks have an intense tip and slightly broadened base, indicating a mixture of nano and small micro particles. On the other hand, the lepidolite peaks are less intense and broadened, indicating their nanostructural consistency. Iron hydroxide, crystallized as goethite, shows a few small peaks, indicating its low concentration in the upper sample. The lower dark red soil (Sample B) has a clayey texture. The relative intensity of the quartz peaks significantly decreases while lepidolite peaks strongly increase compared to the upper layer. Kaolinite peaks are weak and broadened, indicating the presence of a low amount of the finest nanostructured particles. Goethite is present only in weak traces, indicating a small amount of iron hydroxide particles dispersed within the kaolinite. The bottom layer (Sample C) is dominated by a significant presence of quartz, having intense \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multirow{2}{*}{**Sample**} & \multicolumn{3}{c}{**Measured Quantity, g**} & \multirow{2}{*}{**Mean, g**} & \multirow{2}{*}{**SD \(\pm\)**} \\ \cline{3-6}  & & **1** & **2** & **3** & \\ \hline \multirow{3}{*}{A} & Initial & 9.7477 & 10.2263 & 10.1691 & 10.0477 & 0.30 \\  & Settled fraction & 9.2776 & 9.5710 & 9.5281 & 9.4589 & 0.12 \\  & Supernatant fraction & 0.4701 & 0.6553 & 0.6410 & 0.5888 & 0.12 \\ \hline \multirow{3}{*}{B} & Initial & 10.3045 & 9.5119 & 10.2112 & 10.0092 & 0.50 \\  & Settled fraction & 8.0622 & 7.7515 & 7.9988 & 7.9375 & 0.13 \\  & Supernatant fraction & 2.2423 & 1.7604 & 2.2124 & 2.0717 & 0.31 \\ \hline \multirow{3}{*}{C} & Initial & 9.6465 & 10.3412 & 10.1701 & 10.0526 & 0.40 \\  & Settled fraction & 8.0728 & 8.4236 & 8.3214 & 8.2726 & 0.14 \\ \cline{1-1}  & Supernatant fraction & 1.5737 & 1.9176 & 1.8487 & 1.7800 & 0.22 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Samples mass variation through the washing separation process. and narrow peaks. It is followed by kaolinite, which also has well-developed peaks with a slightly broadened base, indicating a mixture of micro and nano fractions. Lepidolite disappears completely on this layer, but the intensity of goethite peaks grows significantly, indicating its relative increase regarding the other constituent minerals. Sample B exhibits an interesting characteristic related to the diffraction peak observed at the position of 26.5\({}^{\circ}\), which commonly fits the most intense peak of the quartz standard PDF 89-8936, but it overlaps with one of the most intense peaks of the manganese lepidolite standard PDF 73-0294. This is more clearly illustrated in Figure 5a, where the quartz position is clearly observed at 26.53\({}^{\circ}\) followed by the lepidolite at 26.57\({}^{\circ}\). Quartz still dominates lepidolite in the composition of Sample B.  
Figure 4: XRD patterns for the soil samples: (**a**) bulk and (**b**) finest fractions collected after washing separation. The peaks’ identification was based on the following PDF files: quartz PDF 89-8936, lepidolite PDF 73-0294, kaolinite PDF 03-0059, and goethite PDF 08-0097. The washing separation process disperses the finest clay particles into ultra-pure water while the coarse fraction settles at the bottom of the recipient. The aqueous dispersion containing the finest fraction is separated and subsequently dried.