Final answer:
The rock with foliation, coarse grains, and porphyroblasts of garnet is Gneiss, a high-grade metamorphic rock with a banded appearance, not to be confused with granite, an igneous rock that lacks foliation.
Step-by-step explanation:
The Rock in Question: Gneiss
The rock described as foliated, coarse-grained, and containing porphyroblasts of garnet is known as Gneiss. Gneiss is a high-grade metamorphic rock that exhibits a banded or layered appearance due to the intense metamorphism it undergoes. This metamorphism causes the minerals within the rock to segregate into alternating bands of light and dark minerals, typically quartz, feldspar, and biotite mica. In some instances, gneiss may contain eye-shaped mineral masses called augen, as is the case with augen gneiss.
It's important to differentiate gneiss from granite, an igneous rock. While both can be coarse-grained, granite forms from the slow cooling and crystallization of magma beneath Earth's surface and does not exhibit the foliated structure characteristic of gneiss. Instead, granite is commonly composed of quartz, feldspars, and amphibole/biotite without having a banded appearance.