Types of metamorphism
1. Contact: from heat and fluids of nearby igneous intrusion
           Hydrothermal Activity, circulation of water through rock, can concentrate rare metals, feed      biological communities
2. Dynamic: where rocks slide past each other, forms mylonite
3. Regional: large-scale, High pressures, usually at plate boundaries

Classification
Foliated: minerals become aligned due to directed stress

Low-grade: slate splits into flat slabs
Intermediate grade: schist, larger crystals grow
High grade: gneiss, banded texture, minerals separate

Beyond gneiss?  Melting (migmatite: part metamorphic/ part igneous rock)

nonfoliated: either no “alignable” minerals OR no directed stress

Marble: from limestone
Quartzite:from sandstone