Metamorphic Rocks
Web-Science.net
UNDER CONSTRUCTION
Metamorphic Rocks - Rocks that have undergone changes in its physical and chemical properties. These
changes are generally due to great heat and pressure.
changes are generally due to great heat and pressure.
Metamorphism - the process where the original rocks undergo recrystallization. Using the original elements, new
compounds are often formed. This is done, however, without melting. Melting the original rocks would then cause
them to become igneous.
compounds are often formed. This is done, however, without melting. Melting the original rocks would then cause
them to become igneous.
is usually easy to distinguish them as metamorphic. However, taking a rock sample and placing it in
a classroom can make it one of the hardest of rocks to classify. Granite and gneiss are so similar
that it is nearly impossible for a non-expert to identify. Only when features such as banding in
gneiss occur does the process become easier.
a classroom can make it one of the hardest of rocks to classify. Granite and gneiss are so similar
that it is nearly impossible for a non-expert to identify. Only when features such as banding in
gneiss occur does the process become easier.
Figure 1
The rock in figure 1 is a banded gneiss from
the Catalina Mountains northeast of Tucson,
AZ. Not only does it show a layering, it also
shows folding. In this case, the white layer
has been folded back over the center darker
layer.
the Catalina Mountains northeast of Tucson,
AZ. Not only does it show a layering, it also
shows folding. In this case, the white layer
has been folded back over the center darker
layer.
To have a basic understanding of the metamorphic process, there are several things you have to
understand:
understand:
- Metamorphism takes place beneath the crust.
- It involves rocks changing from one type to another without becoming a liquid (magma).
- It involves the "agents of metamorphism" to undergo the changes.
Sources:
Agents of metamorphism: http://geology.csupomona.edu/drjessey/class/Gsc101/Meta.html
Agents of metamorphism: http://geology.csupomona.edu/drjessey/class/Gsc101/Meta.html
Agents of Metamorphism
A metamorphic rock, being a rock that has undergone change while maintaining its solid physical
form, begins with a parent rock.
form, begins with a parent rock.
Parent Rock - the original rocks from which a metamorphic rock is formed. The parent rock could have been
sedimentary, igneous, or other metamorphic rocks.
sedimentary, igneous, or other metamorphic rocks.
Agent of Metamorphism - the process that drives the changes in the rock from the parent rock to the final
metamorphic rock. See the discussion on agents of metamorphism for more detail.
metamorphic rock. See the discussion on agents of metamorphism for more detail.