# Microstructural Characterization of the Mn Lepidolite Distribution in Dark Red Clay Soils
## 3 Results
### Microstructural Characterization
A and B. Traces elements of Ca, Mg, and Ti are often found in the forest soils of the Apuseni Mountains [45; 46]. One would expect elemental analysis to identify lithium within the lepidolite particles; however, SEM energy-dispersive spectroscopy (EDS) is unable to detect it because of lithium's small atomic size. Rubidium is the other specific element within the lepidolite formula, which should have been evidenced by the EDS spectra; its energy peak occurs at 1.694 keV, which is very close to the Si peak at 1.739 keV. Since the Si peak is very strong, the detector cannot distinguish the smaller Rb peak, which is confounded with the Si peak base. [PERSON] and [PERSON] investigated lithium ores by SEM-EDX, revealing EDS spectra for pure lepidolite platelets at different acceleration voltages [47]. They revealed the dominant elements as O, Al, Si, and K, which are characteristics of all phyllosilicates. The lepidolite characteristics are spotted by a small energy peak corresponding to F occurring at 0.677 keV and by a stronger Mn peak occurring at 5.894 keV. It is noteworthy that the pure lepidolite ore evidence traces Na and an unassigned energy peak at 3.690 keV that belongs to Ca [47]. These elemental characteristics were obtained at an acceleration of 15 kV, with the Mn peak disappearing at lower acceleration voltages like 5 kV. Thus, the F energy peak is a specific signature for the micas subclass mineral, and Mn represents the lepidolite signature. Our EDS spectra were obtained at an acceleration voltage of 30 kV, ensuring optimal detection of both light and heavy elements. The lepidolite signature was evidenced in both Samples A and B, but the F energy peak was not detected. This phenomenon is explained by the presence of stronger energy peaks from other elements adjacent to its peak position of 0.677 keV, such as O (0.525 keV) and Fe (0.776 keV). It would be interesting to observe if the F energy can be found on the finest fractions separated by washing. The primary washing separation procedure removes the coarser fractions, mainly quartz, increasing the finest clay particle amount in all investigated samples. Thus, Sample A still evidences a sandy morphology based on a few small quartz particles with a boulder-like aspect and sizes up to 10 \(\upmu\)m surrounded by fine lamellar-tabular clay particles, Figure 8a. Some of the clay particles have a planar size up to 5 \(\upmu\)m, and their thickness is about 1.5-2 \(\upmu\)m, but most of them appear as very fine fractions well distributed within the observed microstructure. The elemental map reveals a concentration of blue areas within the finest particles observed, indicating their segregation regarding quartz particles but still mixed with small kaolinite particles. These specific areas look like nanostructured matter clusters, which require an advanced surface investigation. Iron appears as small, concentrated orange-brown spots predominantly dispersed throughout the kaolinite mass, indicating contamination with fine traces of goethite. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \multirow{2}{*}{**Sample**} & \multicolumn{8}{c}{**Elemental Composition, at.\%**} \\ \cline{2-10}  & **O** & **Si** & **Al** & **K** & **Mn** & **Fe** & **Ca** & **Mg** & **Ti** \\ \hline A & 71.6 & 12.4 & 7.0 & 1.4 & 1.9 & 1.3 & 1.2 & 1.1 & 0.2 \\ B & 73.5 & 10.8 & 6.5 & 1.1 & 2.1 & 1.5 & 2.3 & 2.0 & - \\ C & 69.9 & 5.1 & 4.2 & 0.2 & - & 20.6 & - & - & - \\ \hline \end{tabular}
\end{table} 
Table 4: Elemental composition of the initial soil samples. Quartz particles are less prominent in Sample B, Figure 8b, due to their extensive removal during the primary washing separation; however, a few boulder-like quartz particles, approximately 5 \(\upmu\)m in size, are still present and appear bright green on the elemental map. Fine lamellar clay particles dominate the microstructure of Sample B following washing separation.