The process of formation of metamorphic rocks starts with existing rocks. Then, they undergo some sort of change due to immense heat or pressure. For example, a rock made of sand is “metamorphosed” into another type of rock when it comes in contact with intense heat. They can’t melt because then it would be heading for the igneous state...
Britannica Kids-Metamorphic Rock
Metamorphic rocks are formed when other rocks are affected by great temperatures and pressures. They do not melt, but the chemicals they contain may change their forms, or crystal shapes. Marble and slate are two examples of metamorphic rocks. The name metamorphic comes from Greek words meaning “change of shape.”...
Metamorphic rock explained with examples
Metamorphic rock introduction, the rock cycle, and types