Because their chemistry changes based on temperature and pressure, they help geologists "read" the history of a mountain range or a volcanic eruption.
This is where they truly shine. Amphiboles are the star of the Amphibolite facies , a stage of medium-to-high grade metamorphism. They form when basaltic rocks are subjected to intense heat and pressure in the presence of water. Amphiboles: Crystal Chemistry, Occurrence, and ...
They are primary minerals in intermediate to felsic rocks. If you see dark, needle-like crystals in diorite , andesite , or granite , you’re likely looking at Hornblende—the most common amphibole. Because their chemistry changes based on temperature and