How does heat and pressure change minerals?
The presence of some specific minerals in a metamorphic rock can indicate the degree of heat and pressure it sustained. Metamorphic rocks are sedimentary or igneous rocks that have been modified or changed in form, that is, the size, shape and arrangement of the minerals in rocks, by heat or pressure.
For metamorphism to occur energy is needed to fuel the chemical reactions. Heat is the primary source of this energy.
The pressure within the earth is the result of gravity pulling the crust of the earth downward.Like heat, pressure increases with depth. This pressure can actually squeeze the spaces out of the minerals within the rock. This makes the rocks denser. The heat and pressure together cause the rock to flow instead of break or fracture. The mineral grains become realigned. They flatten out and get longer.