What is characteristic of the assemblage containing albite, chlorite, actinolite, and calcite?

The assemblage containing albite, chlorite, actinolite, and calcite is characteristic of the greenschist facies, which indicates specific conditions of metamorphism. The greenschist facies typically forms under moderate temperature and pressure conditions, specifically in the range of 300 to 500 degrees Celsius and pressures of approximately 3 to 10 kilobars.

In this metamorphic environment, the minerals present reflect the lower greenschist metamorphic conditions. Albite, a sodium-rich plagioclase feldspar, often forms during the alteration of feldspars in the presence of fluids, which is common in greenschist facies rocks. Chlorite, a common green mineral in this facies, usually forms from the alteration of biotite or other mafic minerals. Actinolite, which is an amphibole mineral, indicates the presence of specific conditions conducive to the metamorphism of basaltic rocks. Calcite, a carbonate mineral, might indicate the presence of limestone or calcareous sediments that have undergone metamorphism.

These minerals combined are indicative of the chemical reactions and stability of materials under the specific pressures and temperatures associated with the greenschist facies, setting it apart from metapelites (like