# Mineral Powder Extraction by the Natural Drying of Water from the Public Springs in Borsec
## Results
### Mineral Crystallization Assessment
The calcite and pseudo-dolomite crystals are colored in white-yellow at the maximum and brown at the extinction position. The crystal habit is very important for proper identification: calcite crystals are predominantly rhombic and pseudo-hexagonal while dolomite crystals are predominantly columnar prisms. Natron crystals appear yellow at the maximum lighting and gray-yellow at extinction featuring needle shapes due to their monoclinic crystallization. Figure 4: POM images of the crystals’ development in the water samples collected in the first campaign: (**a**) Spring 3, (**b**) Spring 5, (**c**) Spring 6, (**d**) Spring 10, and (**e**) Spring 11; (**l**) individual grains crystallized from the water samples; (**2**) grains embedding in the final dendritic crystalline crust; and (**3**) milled crystalline crust powder which was subjected to the XRD investigation. The early stage of crystallization within the S3 sample features small micro-crystals that are well individualized without coalescence and that were formed by the alkaline ions' reaction with carbonic acid, as shown in Figure 4(a1). Fine crystals of calcite, pseudo-dolomite, and aragonite appear along with a few fine yellow needles of natron. Halite crystals do not appear in this early stage. The final stage of the crystallization process leads to a supersaturated solution that accelerates the crystallization process, and the individual crystals are covered by additional layers and, finally, when the water is almost completely evaporated, a crystalline crust is formed generating a dendritic chain microstructure; see Figure 4(a2). Halite crystallizes during this stage, the formed crystals being embedded in the crust on the dendrites' borders; this fact is proved by the pale blue shade observed on the surface of the crystal. Figure 5: POM images of the crystals’ development in the water samples collected in the second campaign: (**a**) Spring 3, (**b**) Spring 5, (**c**) Spring 6, (**d**) Spring 10, and (**e**) Spring 11; (**1**) individual grains crystallized from the water samples; (**2**) grains embedding in the final dendritic crystalline crust; and (**3**) milled crystalline crust powder which was subjected to the XRD investigation. their sides, as shown in Figure 4(a2). This indicates that halite crystallizes as thin cubic platelets covering the previously formed crystals. Figure 4(a3) reveals the microstructural aspect of the crystalline powder resulting after the scratching of the crystalline crust. The general aspect is colored pale white due to the large calcite and pseudo-dolomite contents, and the individualized crystals appear embedded into the broken dendrite mass (this powder was used for the XRD). The S5 sample has more crystallization centers and develops finer crystals, as observed in Figure 4(b1). The calcite and pseudo-dolomite crystals are the most evident on the observation field, and there are some rhombic crystals colored in blue-violet colors belonging to the aragonite (they are most likely observed after the intense blue spots). The natron crystals are difficult to observe but some finer yellow acicular intercalations can be observed in the central area of the observation field in Figure 4(b1). Halite crystals are not yet formed, and the sodium chloride is still remnant in the supersaturated solution. The intensive evaporation of water during the final stage causes massive crystallization including halite and natron along with the rest of the calcite and pseudo-dolomite forming a dense dendritic structure, seen in Figure 4(b2). The dendrites are grouped in growths of local inflorescences on the corners of some individualized rhombic and pseudo-hexagonal individual calcite crystals. The dendrites contain a fine succession of calcite and dolomite crystallites that will be better observed by the SEM investigation. Their faster growth under the final concentration gradient during drying caused the embedding of most of the free crystals formed in the first stage.