When granite rocks undergo metamorphism under suitable temperature and pressure conditions, they are converted into which of the following metamorphic rocks?

Introduction / Context:
This question comes from geology and earth science, which are often included under general science or general knowledge. It asks which metamorphic rock is formed when granite, an igneous rock, is subjected to metamorphism. Knowing the parent rock and its metamorphic product is useful in understanding rock cycles, tectonic processes and the classification of rocks. Granite is a coarse grained igneous rock, and metamorphism changes its texture and mineral alignment to produce a distinct metamorphic rock type.

Given Data / Assumptions:
Granite is an intrusive igneous rock composed mainly of quartz, feldspar and mica.
Metamorphism involves changes in mineral structure and texture under heat and pressure without complete melting.
Quartzite is a metamorphic rock derived from sandstone rich in quartz.
Marble is a metamorphic rock derived from limestone or dolomite rock.
Slate is a metamorphic rock derived mainly from shale or mudstone.

Concept / Approach:
The key concept is the rock cycle and parent rock metamorphic rock relationships. Granite subjected to regional metamorphism, involving high pressure and temperature, can develop foliation, where minerals such as mica align in bands. The resulting rock is called gneiss, which displays characteristic banding and segregation of light and dark minerals. Quartzite, marble and slate each have different sedimentary parent rocks, so they cannot be the direct products of metamorphism of granite. By matching the parent rock granite with the correct metamorphic product, we identify gneiss as the correct answer.

Step-by-Step Solution:
Step 1: Recall that granite is an igneous rock formed from slow cooling of magma and composed primarily of quartz, feldspar and mica. Step 2: Under regional metamorphic conditions, granite can be subjected to high pressures and temperatures that cause mineral grains to recrystallise and align, creating a banded texture. Step 3: The metamorphic rock that forms from granite in this way is called gneiss, which is distinguished by its coarse banded structure with alternating layers of light and dark minerals. Step 4: Quartzite forms from metamorphism of quartz rich sandstone, not from granite, so it cannot be the product of granitic metamorphism. Step 5: Marble forms from limestone or dolomite rock, and slate forms from shale, so neither is a metamorphosed form of granite, confirming that gneiss is the correct choice.

Verification / Alternative check:
Geology textbooks and rock classification charts show parent rock metamorphic rock pairs such as sandstone quartzite, limestone marble, shale slate and schist, and granite gneiss. Field studies and thin section analyses confirm that gneiss often has mineral assemblages similar to granite but exhibits strong foliation and banding due to metamorphic processes. In contrast, quartzite is nearly pure quartz, marble is primarily calcite or dolomite and slate has fine grained mica and clay minerals derived from shale. These independent observations confirm that granite metamorphoses into gneiss, not into the other listed rocks.

Why Other Options Are Wrong:
Quartzite is wrong because it is formed by metamorphism of quartz rich sandstone and does not originate from granitic parent rock.
Marble is wrong because it forms from limestone or dolomite rocks under metamorphic conditions and contains calcite or dolomite rather than the feldspar rich composition of granite.
Slate is wrong because it is derived from shale or mudstone and is fine grained, whereas granite is coarse grained; the textural and compositional mismatch makes slate an incorrect product of granite metamorphism.

Common Pitfalls:
Students may incorrectly match rocks based only on name familiarity or on the assumption that all metamorphic rocks can form from any parent. Another pitfall is confusing quartzite and gneiss because both can be hard and resistant, but their textures and origins are different. Remembering a simple mapping of parent to metamorphic rocks, such as granite gneiss and sandstone quartzite, helps to avoid such confusion. Visualising the banded nature of gneiss versus the massive granular nature of quartzite is another useful cue.

Final Answer:
When granite rocks are metamorphosed, they are converted into the metamorphic rock Gneiss.