Step-by-step explanation:
The porphyritic texture is very common in igneous rocks, it consists of larger crystals (phenocrysts) that are embedded in a fine-grained groundmass or matrix (I annexed an image of this structure). This kind of texture indicates that the magma sat and cooled a bit below the Earth's surface, giving time for the large crystals to grow, before erupting onto the surface and cooling very quickly.
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