Civil Engineering - Building Materials - Discussion

Gneiss is a type of metamorphic rock which is formed when granite is metamorphized.

Metamorphic rocks formed from the transformation of existing rock types by a process called metamorphism. Metamorphic rocks make form 12% of the Earth's land surface.

Common examples of metamorphic rocks are quartzite, gneiss, slate, schist, marble, etc.

Marble is a metamorphic rock formed from limestone.
Slate is a metamorphic rock formed from shale and mudstone.
Gneiss is a metamorphic rock formed from granite.
Graphite is a metamorphic rock formed from coal.

Gneiss is a metamorph of conglomerate also which is a sedimentary rock, in that sense, according to options, the best answer is sedimentary metamorphic rocks.

Gneiss is obtained from a conglomerate too which is a sedimentary rock. So the given answer is right.

Slate is the sedimentary rocks, due to the excess action of heat and pressure, the slate changes to gniess. This process is called metamorphism. So, it is sedimentary metamorphic rocks.

Metamorphic rocks is the right answer.

Gneiss, a metamorphic rock that has a distinct banding, which is apparent in hand specimens or on a microscopic scale. Gneiss is usually distinguished from schist by its foliation and schistosity; gneiss displays a well-developed foliation and a poorly developed schistosity and cleavage.

Option A is the correct answer.

Gneiss is obtained from metamorphic rock and it is formed by metamorphism of sedimentary and igneous rock.

Option D is wrong.

Gneiss is obtained from Granite which is an igneous rock.

So, option A is correct.