What are metamorphic rocks? American Geosciences Institute

Metamorphic rocks are rocks that have become changed by intense heat or pressure while forming. In the very hot and pressured conditions deep inside the Earth’s crust, both sedimentary and igneous rocks can be changed into metamorphic rock. In certain conditions these rocks cool and crystallize usually into bands of crystals. Later they can become exposed on Earth’s surface. One way to tell if a rock sample is metamorphic is to see if the crystals within it are arranged in bands.

Why are metamorphic rocks the hardest? - Quora

8 Metamorphic Minerals and Metamorphic Rocks – Mineralogy

Metamorphic rock - Wikipedia

8 Metamorphic Minerals and Metamorphic Rocks – Mineralogy

Rocks and minerals - British Geological Survey

An absentee note for ancient blueschist: Lack of metamorphic rock does not date onset of plate tectonics

Metamorphic Rocks Geological Society of Glasgow

The Geoscience Handbook, AGI Data Sheets Fifth Edition

Metavolcanic rock - Wikipedia

Metamorphic processes - The Australian Museum