When high temperatures and pressures combine to alter the texture, mineralogy, or chemical composition of rock without melting it, the process is called metamorphism.

Here's a breakdown of what happens:

* High temperatures: Heat from magma intrusions or deep burial within the Earth can cause existing minerals in the rock to recrystallize or transform into new minerals.

* High pressures: Pressure from the weight of overlying rocks can also cause minerals to recrystallize and change their arrangement. This pressure can be directional, leading to the formation of foliation (layers) in metamorphic rocks.

* Chemical reactions: Fluids circulating through the rock can react with existing minerals, changing their composition.

Metamorphism doesn't melt the rock, it simply changes its form. This results in the creation of metamorphic rocks, which have distinct textures and minerals compared to their original, un-metamorphosed counterparts.

Here are some examples of metamorphic rocks:

* Slate: Formed from shale by low-grade metamorphism.

* Marble: Formed from limestone or dolostone by high-grade metamorphism.

* Gneiss: Formed from various rocks by high-grade metamorphism, often displaying banding of different minerals.

The resulting metamorphic rock depends on the original rock type, the intensity of the heat and pressure, and the chemical environment.