There are several types of coal, which you will learn about in a later lab. Metamorphism causes changes in the texture and mineralogy of other rocks. 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 .