If we have to igneous rocks, and they have the same minerals, that doesn't necessarily means that they will have the same name, thus being classified as the same rock. The reason for this is that the two igneous rocks may have a different texture. One of the rocks may have a foliated, while the other may have porphyritic, giving them different appearance despite the same minerals being in both of them. The reason why two igneous rocks with the same minerlas may appear different, is the process in which they have been formed, the quickness of the cooling, the temperature that they were exposed to, and the pressure they were exposed to.
