Phyllite, schist, gneiss, quartzite and marble are examples of:

Metamorphic rocks (from the Greek words meta, meaning "change", and morphe, meaning "form") are formed when existing rocks, igneous, sedimentary or even older metamorphic rocks, are changed by great heat, pressure or chemically active fluids, without melting. This process is called metamorphism. It usually happens deep inside the Earth, near masses of hot magma, or where tectonic plates collide and mountains are formed.

During metamorphism, the minerals in the rock may recrystallise, and new minerals may form. Often, the minerals line up in parallel bands or layers because of pressure. This banding is called foliation. Rocks such as slate, schist and gneiss are foliated. Others, such as marble and quartzite, are non-foliated.

Common examples of metamorphism:

Limestone changes into marble. Marble is used for buildings and sculptures; the Taj Mahal is built of white marble from Makrana in Rajasthan.

Sandstone changes into quartzite, a very hard rock.

Shale changes into slate, which splits into thin sheets and was used for roofing and writing slates. With more heat and pressure, slate changes into phyllite and then into schist.

Granite changes into gneiss, which has a banded appearance.

Coal changes into graphite under intense heat and pressure.

In India, metamorphic rocks are found in the Aravalli Range, parts of the Himalaya (the Lesser Himalaya has many metamorphosed sedimentary rocks), and the Peninsular Plateau, including the ancient Dharwar system, which is rich in minerals such as iron ore and gold.

Why not the other options?

• ✗Igneous rocks form from magma or lava, such as granite and basalt.
• ✗Sedimentary rocks form from layers of sediment, such as sandstone, shale and limestone.
• ✗Volcanic rocks are extrusive igneous rocks, such as basalt and pumice.