Here's why:

* Melting: When rocks melt, they become magma (underground) or lava (above ground). This marks the beginning of the igneous rock cycle. Once cooled and solidified, the result is an igneous rock.

* Metamorphism: Metamorphic rocks are formed when existing rocks (igneous, sedimentary, or even other metamorphic rocks) are transformed by heat and pressure without melting. The minerals within the rock change and rearrange, creating new textures and sometimes new minerals.

Key difference: Metamorphism involves solid-state transformation. The rock doesn't melt, it simply changes its structure and composition while remaining solid.

Example:

* Limestone (sedimentary rock) under intense heat and pressure can be transformed into marble (metamorphic rock).

* Sandstone (sedimentary rock) can become quartzite (metamorphic rock) through the same process.

Let me know if you have any other questions!