When rocks are metamorphosed their bulk chemistry remains about the same, except for water and CO2, which are fairly mobile. The mineral assemblages constantly change but the chemistry remains the same. Thus, the temperature and pressure of metamorphism control the mineral assemblages in metamorphic rocks. In 1915, a famous petrologist named Pentti Eskola presented the concept of meta-morphic facies, stating that different assemblages of metamorphic minerals that reach equilibrium during metamorphism within a specific range of physical conditions belong to the same metamorphic facies.
Eskola studied rocks of basaltic composition, so he named his facies according to the metamorphic names for basaltic rocks. His classification, shown in the upper figure on page 541, stands to this day.
Was this article helpful?
Preparing for Armageddon, Natural Disasters, Nuclear Strikes, the Zombie Apocalypse, and Every Other Threat to Human Life on Earth. Most of us have thought about how we would handle various types of scenarios that could signal the end of the world. There are plenty of movies on the subject, psychological papers, and even survivalists that are part of reality TV shows. Perhaps you have had dreams about being one of the few left and what you would do in order to survive.