Which one of the following is not a Metamorphic Rock ?

Question

Accepted Answer

Option 4, Gabbro, is the correct answer because it is not a metamorphic rock. Instead, Gabbro is an igneous rock. Igneous rocks form from the solidification of molten magma or lava. Gabbro specifically forms when magma cools slowly beneath the Earth's surface, resulting in a coarse-grained texture. This process is distinct from the formation of metamorphic rocks, which are created through the alteration of existing rocks under high pressure and temperature conditions without melting.

Now, let's explain why the other options are incorrect:

1. **Marble**: Marble is a metamorphic rock that forms from the recrystallization of limestone or dolomite under high pressure and temperature conditions. The process results in a denser rock with a crystalline texture, which is characteristic of metamorphic rocks.

2. **Quartzite**: Quartzite is another example of a metamorphic rock. It originates from sandstone that has undergone metamorphism. During this process, the quartz grains in the sandstone are fused together, forming a hard and dense rock known as quartzite.

3. **Graphite**: Graphite is also considered a metamorphic rock. It forms from the metamorphism of carbon-rich materials, such as coal, under high pressure and temperature. Graphite's crystalline structure and properties are a result of this metamorphic process.

In summary, Option 4, Gabbro, is correctly identified as not being a metamorphic rock because it is an igneous rock, whereas Marble, Quartzite, and Graphite are all metamorphic rocks formed through the transformation of pre-existing rocks under specific conditions.