Which rock is formed from granite by high-grade metamorphism?

Which rock is formed from granite by high-grade metamorphism?

• A. Gneiss
• B. Quartzite
• C. Marble
• D. Schist

Answer: (A)

When granite is subjected to high-temperature and high-pressure metamorphism, its minerals recrystallize and separate into distinct bands of light and dark minerals. This creates a strongly foliated, banded texture known as gneiss. The light bands are typically rich in quartz and feldspar, while the dark bands contain minerals like biotite or hornblende. This banded appearance and mineral segregation are hallmarks of high-grade metamorphism of a granitic composition, so the rock formed from granite under those conditions is gneiss. Quartzite forms from quartz sandstone and remains non-foliated, lacking the pronounced banding of gneiss. Marble comes from limestone and likewise is typically non-foliated or only weakly foliated. Schist results from metamorphosing clay-rich rocks (like shale) or other protoliths and shows pronounced platy minerals and schistosity, but it’s not the product of granite under high-grade conditions.

When granite is subjected to high-temperature and high-pressure metamorphism, its minerals recrystallize and separate into distinct bands of light and dark minerals. This creates a strongly foliated, banded texture known as gneiss. The light bands are typically rich in quartz and feldspar, while the dark bands contain minerals like biotite or hornblende. This banded appearance and mineral segregation are hallmarks of high-grade metamorphism of a granitic composition, so the rock formed from granite under those conditions is gneiss.

Quartzite forms from quartz sandstone and remains non-foliated, lacking the pronounced banding of gneiss. Marble comes from limestone and likewise is typically non-foliated or only weakly foliated. Schist results from metamorphosing clay-rich rocks (like shale) or other protoliths and shows pronounced platy minerals and schistosity, but it’s not the product of granite under high-grade conditions.