Metamorphic Facies
Metamorphic Rock Names
Outline
As the degree of metamorphism increases, new minerals become stable and crystallize. The minerals present in a metamorphic rocks are thus indicators of the P/T conditions at the time of the last recrystallization. Metamorphic Grade is a scale of metamorphic intensity which uses indicator minerals as geothermometers and geobarometers.
SLATE -> PHYLITE -> SCHIST is a sequence of metamorphic rocks of increasing grade. The corresponding indicator minerals are chlorite, biotite and garnet. The transition from chlorite grade to biotite grade is the first appearance of chlorite.
The numerical temperature ranges of the indicator minerals are shown in the diagram. At the introductory level, the temperatures and the mineral names are not important but the principles of geothermometry and geobarometry are the key to unravelling metamorphic history of a region.
Metamorphic Facies
Metamorphic Rock Names
Outline