Meta = change
Morph = form
The transition of one rock into another by temperatures and/or pressures unlike those in which it formed. Metamorphic rocks are produced from:
- Igneous rocks
- Sedimentary rocks
- Other metamorphic rocks
Parent rocks are called “protoliths.” Metamorphic rocks often look totally unlike their protoliths.
Metamorphism occurs in the solid state. If the temperatures and pressures acting upon the rock cause it to melt, the resulting rock will be igneous, not metamorphic.
Metamorphic rocks have distinctive properties.
- Unique texture – Intergrown and interlocking grains.
- Unique minerals – Some that are only metamorphic.
- Unique foliation – A planar fabric from aligned minerals