Metamorphic
Definition
Rocks or minerals formed by the transformation of existing rocks under high temperature and pressure conditions.
Example
Garnet commonly forms in metamorphic rocks like schist and gneiss.
Rocks Transformed
Metamorphic rocks have been "changed" (meta) in "form" (morph) by heat and pressure without melting into liquid magma. If the rock melts, it becomes igneous. Metamorphism occurs deep within the Earth or at tectonic plate boundaries where mountains are built. The immense pressure forces minerals to realign or recrystallize into new minerals that are stable at those conditions.
Types of Metamorphism
- Regional Metamorphism: Occurs over vast areas during mountain building. Pressure causes minerals to align in layers (foliation). Slate, Schist, and Gneiss are examples.
- Contact Metamorphism: Occurs when hot magma touches surrounding cold rock, "baking" it. This often creates non-foliated rocks like Marble (from limestone) and Hornfels, and is a prime environment for forming gemstones like Garnet and Spinel.