Eventually the idea of metamorphic facies developed
that included contact and regional metamorphism. These facies were
defined by geologists in the field, but also experimental data helped to
define the minerals more precisely. A facies is a metamorphic mineral
assemblage that provides a geologist with a predictable relation between
mineral composition and chemical composition with respect to the
pressure and temperature of its formation.
These metamorphic facies are defined by the
minerals and corresponding rocks that they produce. Some of the minerals
and rocks we have not discussed, but this facies concept is an important
way of relating rocks in time and space. In the exercise you are read
the graphs to try and derive information.