## 3 Results and Discussion  
The Interaction of Obsidian with the Reaction Mixture Favored the Synthesis of Biomorphs with a Crystalline Phase of the Rontgenite Polymorph  
When the SEM samples were analyzed, we observed that the morphology that the biomorphs adopted was dependent on the conditions of the method of synthesis. In the case of the control biomorphs using calcium synthesized on glass under standard pressure and temperature conditions (that is, the current conditions), they adopted a conventional polycrystalline shape (Figure 1a). In contrast, the control biomorphs obtained at 5% CO\({}_{2}\) and 50 \({}^{\circ}\)C (that is, Precambrian conditions) presented a rhombohedral morphology (Figure 1b). In the case of the silico-carbonate of the calcium biomorphs obtained on the obsidian at an ambient temperature (Figure 1c), the shape that appeared was polycrystalline, just like the biomorphs produced on glass (Figure 1a). Meanwhile, the silico-carbonate of the calcium biomorphs synthesized on the obsidian under conditions that emulated the Precambrian atmosphere (50 \({}^{\circ}\)C in the presence of 5% CO\({}_{2}\)) adopted a rhombohedral morphology (Figure 1d), as did those synthesized on glass (Figure 1b). The difference in the shapes adopted by the biomorphs under the two synthesis conditions is due to the fact that the calcium biomorphs obtained under the Precambrian conditions were synthesized at a high concentration of CO\({}_{2}\) and a higher temperature, compared with the calcium biomorphs produced under the standard atmospheric conditions of ambient CO\({}_{2}\) and temperature. It has been shown in work by this research group and other groups that atmospheric conditions play an important role in the form that biomorphs adopt [27; 31; 33]. The morphology or crystalline aggregate of the silico-carbonate of the calcium biomorphs observed in these two tested conditions was found to be in agreement with that previously reported [27; 31; 33]. It has been reported that the morphology adopted by the biomorphs depends on various factors, such as the nucleation conditions of the crystalline cell and the interactions of the elements between the support and the medium where this interaction takes place, thus forming the crystalline structures of the different morphologies seen in the resulting biomorphs [15; 16; 17; 18; 19; 20; 21; 22; 23; 34; 35]. Additionally, our results are in agreement with a surface engineering study in which spontaneous growth produces surface microstructure engineering through a natural surface phenomenon similar to ion secretion precipitation, that is, coupled dissolution precipitation [36; 37; 38; 39]. To identify and characterize the biomorphs (the control), as well as those synthesized on obsidian, in both atmospheric conditions, analyses were carried out using Raman and FTIR spectroscopies and PXRD. The biomorphs synthesized under ambient conditions showed Raman bands at 160, 285, 714, and 1087 cm\({}^{-1}\) (Table 1). Whereas in the biomorphs obtained under Precambrian-like conditions, bands at 162, 287, 717, and 1089 cm\({}^{-1}\) were identified (Table 1). The vibrations identified correspond to the calcite polymorph [40]. These results are consistent with those reported in other studies under these synthesis conditions [31]. The polymorphs were corroborated by IR (Table 1). When performing the Raman analysis of the biomorphs synthesized on obsidian at room temperature, bands were observed at 157, 282, 713, and 1086 cm\({}^{-1}\) (Figure 2b, Table 1). Figure 1: Micrographs of calcium silica-carbonate biomorphs obtained via SEM on glass (**a**,**b**), on obsidian (**c**,**d**), under (**a**,**c**) ambient temperature and (**b**,**d**) conditions emulating the Precambrian atmosphere. Figure 2: Characterization and identification of the calcium silica–carbonate biomorphs synthesized on obsidian under standard atmospheric conditions.