Metamorphic Bedrock
In Greek, "meta" means change and "morphe" means form or shape. Your students will be familiar with this word because of "Power Rangers" (who change characteristics). So it is with metamorphic rocks. The crystals of a metamorphic rock change physically and chemically through the process of metamorphism. The rock looks different and is different from before. Sometimes the changes are minor. Sometimes changes obliterate the characteristics of the original rock.
| Chemical Processes | Physical Processes |
| changed chemical structure | heat and pressure |
| more than one chemical process | |
Both chemical and physical processes |
|
When metamorphism has only barely changed bedrock it is called low-grade metamorphism. When heat and pressure are so intense that they have dramatically affected the physical and chemical properties of crystals it is called high-grade metamorphism. If the rock is melted it is no longer metamorphic.
NOTE: When pressure and heat finally melt the rocks, the result is NOT metamorphic rocks, it is igneous rock. This is the big difference between metamorphic and igneous rock. Igneous rocks were once melted rock.