The Mezosoic was marked by significant changes, resulting from the rupture of the megacontinent Gondwana and opening of the Central Atlantic Ocean, establishing a stage of tectonic activation, marked by intense tholeiitic magmatism. In Parnaiba Basin, these events are recorded in the lithostratigraphic units Mosquito Formation and Sardinha Formation. The mineralogical, textural and petrographic characterization of the amygdaloidal basalts of the Mosquito Formation in its occurrence in the Zé Queiroz Quarry, located in the city of Porto Franco (MA), made possible to infer their conditions of magmatic crystallization and to correlate them with rocks of similar suites. The petrographic analysis allowed the mineralogical assemblage of these rocks to be determined mainly by plagioclase, augite, ilmenite and cryptocrystalline to vitreous matrix, and pigeonite and titanomagnetite may be present, and also zeolites, titanomagnetite and green cryptocrystalline material filling the amygdales, and as secondary minerals, clay minerals and epidote. The textures found in these rocks are porphyritic and intersertal; and the amygdaloidal, glomeroporphyritic, skeletal, subophitic and variolytic textures still occur. The results of this study led to the recognition of two petrographic types of basalt: microporphyritic basalt with plagioclase and augite phenocrysts and glass-bearing basalt. The proposed crystallization model suggests that crystallization occurred in two stages: I) formation of the opaque minerals, in depth, followed by the crystallization of the essential phases, generating phenocrysts; II) the magma rises to the surface and forms a glassy microcrystalline matrix, the presence of volatiles in the magma generates vesicles, which, in a post-magmatic phase, are filled with zeolites and iron oxides. Finally, after the crystallization, the percolation of fluids led to the formation of secondary phases, such as the clay minerals and epidote, besides the devitrification of the vitreous matrix. The comparison made between the studied rocks and the Penatecaua Magmatism rocks (Amazonas and Solimões Basins) and the Apoteri Suite (Tacutu Basin), described in the literature, suggests a similarity between the mineralogical and textural compositions of these rocks, besides indicating chronological correlation between the suites.
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