Metamorphic rocks are the one type of rock that forms only in the subsurface. This type of rock forms as a result of intense heat and pressure. The intense heat and pressure physically and chemically alter the minerals in the existing rock. This environment is found at convergent boundaries or where molten magma is near existing rock.
Metamorphic rocks can be categorized as foliated or non-foliated. Foliated metamorphic rocks have a unique characteristic of having a layered look. The parent rock (rock that is being changed into a new rock) has minerals that are platy and the intense heat and pressure force those minerals to stretch and align into layers. This characteristic can be seen in slate. The intense pressure causes this flattening out of the minerals to give this layered appearance.
Non-foliated metamorphic rocks do not have a uniform arrangement of the minerals. The parent rock does not contain minerals that are platy and therefore when they are recrystallized by heat and pressure, there is no internal arrangement of the minerals as they recrystallize. Marble is a common non-foliated metamorphic rock.
The bottom of the formation is Uncompahgre quartzite, approximately 1.3 billion years old.
Image Credits
- slate-in-Colorado: Photo Credit: Sabrina Ewald
- Box-Canyon-CO (unconformity): Photo Credit: Sabrina Ewald
