Rocks formed due to alteration of original structure under heat and excessive pressure are
- ASedimentary rocks
- BIgneous rocks
- CMetamorphic rocksCorrect
- DNone of the above
Solution
Concept
Formation of metamorphic rocks
Formula
NONE
Step-by-step solution
1. Pre-existing igneous or sedimentary rocks undergo physical and chemical changes when subjected to high heat and pressure. 2. This process of structural and mineralogical alteration is known as metamorphism. 3. Rocks formed through this alteration process are classified as metamorphic rocks. Answer: C
Explanation
Metamorphic rocks are formed when pre-existing igneous, sedimentary, or metamorphic rocks are subjected to high temperatures and intense pressure deep within the Earth. These physical conditions alter the texture and mineral composition of the rock without melting it. Therefore, rocks changed by heat and pressure are metamorphic rocks.
Why the other options are wrong
A) Sedimentary rocks are formed by the consolidation and cementation of rock sediments. B) Igneous rocks are formed by the cooling and solidification of magma or lava. D) Option C is correct as metamorphic rocks are formed under heat and pressure.
Shortcut
"Meta" (change) + "morph" (structure): Metamorphic rocks change under heat and pressure.
Common mistake
Confusing metamorphic rocks with igneous rocks formed from cooling molten magma.
Correct answer: C) Metamorphic rocks