Answer:
D.a magma that has partially crystallized slowly moves to a different location where it then cools rapidly.
Explanation:
Porphyritic texture -
It is specifically formed on the igneous rocks , for the rock which has some difference between crystal size , where one group of crystal is larger than the other group .
Porphyry is one the main type of rock which have porphyritic texture .
Formation of the Porphyritic rocks -
These types of rocks are formed when the rising magma is cooled via two stages , in the stage one , the cooling process is done slowly deep in the crust and forming large crystal grains .
In the step two , the cooling is done rapidly , at shallow depth
