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Basalt glasses may form glass‐ceramic materials upon a thermal treatment (TT) if the Fe2O3/FeO ratio is greater than 0.5. In this work, a Serra Geral Formation basalt was used to produce different glass‐ceramic materials by changing its chemical composition, removing Fe2O3 via magnetic separation and adding 20 wt% Fe2O3. Glass‐ceramics were prepared by melting at 1500°C, followed by a crystallization plateau at 950°C. This petrurgic TT yields dendritic structures upon surface crystallization. With the increase of the iron content, crystallization was more pronounced, as observed in thermal analysis results and optical/scanning electron microscopy. The microstructure analysis shows that these glass‐ceramics exhibit at least two different types of crystallization. On the surface, the predominant crystallization was dendritic, while in bulk, crystallization occurred in the form of randomly distributed submicrometric spheroid crystals.