THE MANY FACIES OF METAMORPIC ROCKS
A rock is made of minerals that are stable in a given
environment. If the physical conditions of a rock change, especially
temperature and pressure, the minerals will not be stable. A new group
of minerals will begin forming under metamorphism until the environment
becomes stable again. These mineral assemblages will appear depending on
The initial composition of a rock is very
important. This will decide what it will become with changing
metamorphic conditions. A rock with the same composition can turn into a
different metamorphic rock, depending on the pressure and temperature.
If the pressure and temperature are the same, the initial rock control
the path metamorphism takes.