They do not melt, but the minerals they contain are changed chemically, forming metamorphic rocks. Sometimes, metamorphic rocks are formed when rocks are close to some molten magma, and so get heated up. Remember that metamorphic rocks are not made from melting rock. (Rocks that do melt form igneous rocks instead.)

Formation of Metamorphic Rocks

Metamorphic rocks are formed through a process known as metamorphism, which occurs deep within the Earth's crust under intense heat and pressure. This process causes the minerals and textures of existing rocks to change, resulting in the formation of new rocks with different physical and chemical properties. Let's delve into the details of how metamorphic rocks are formed.

1. Heat and Pressure
Metamorphism primarily occurs due to the combined effects of heat and pressure. Heat is generated by the Earth's internal heat sources, such as magma, which raises the temperature of rocks. Pressure is exerted on rocks by the overlying layers of rocks and sediments.

2. Recrystallization
As the temperature and pressure increase, the minerals in the original rocks undergo recrystallization. This process involves the rearrangement of atoms within the minerals, resulting in the formation of new crystal structures. Recrystallization can cause the growth of larger mineral crystals or the development of entirely new minerals.

3. Texture Changes
Metamorphism also leads to changes in the texture of rocks. The original rock's texture, such as the size and shape of mineral grains, can be altered during metamorphism. For example, a fine-grained sedimentary rock may transform into a coarse-grained metamorphic rock due to the growth of larger mineral crystals.

4. Pressure Solutions
Pressure solutions are another important mechanism in metamorphic rock formation. Under high-pressure conditions, minerals can dissolve at grain boundaries and recrystallize in areas of lower pressure. This process can result in the alignment of mineral grains and the development of preferred orientations, known as foliation.

5. Fluids and Chemical Reactions
Fluids, such as water and dissolved minerals, play a crucial role in metamorphism. They can facilitate chemical reactions between minerals, leading to the formation of new minerals or the alteration of existing ones. These chemical reactions can result in changes in rock composition and the formation of distinct metamorphic rock types.

6. Types of Metamorphism
Metamorphism can occur in different settings, each yielding distinct types of metamorphic rocks. Regional metamorphism occurs over large areas and is associated with tectonic processes, such as mountain building. Contact metamorphism occurs when rocks come into contact with hot magma, resulting in localized changes. Dynamic (or cataclastic) metamorphism occurs along fault zones, where rocks experience intense pressure and shearing.

Conclusion
Metamorphic rocks are formed through the process of metamorphism, which involves the transformation of existing rocks under high heat and pressure conditions. This transformative process leads to changes in mineral composition, texture, and the formation of new rock types. Understanding the formation of metamorphic rocks provides valuable insights into the Earth's dynamic processes and the geological history of our planet.

Sometimes due to high pressure and temperature , both igenous and sedimentary rocks undergo a complete change in their appearance and composition and form a complete different rock . Such rock are called metamorphic ricks