Rocks formed along fault zones are called mylonites . Many metallic ore deposits form in this way. The processes of compaction and recrystallization change the texture of rocks during metamorphism. The grains move closer together. The rock becomes more dense.
Porosity is reduced.
No changes in overall chemistry. New crystals grow from the minerals already present. A preferred orientation of minerals commonly develops under applied pressure. Platy or sheet-like minerals such as muscovite and biotite become oriented perpendicular to the direction of force. This preferred orientation is called foliation .