GeoClassroom Physical Geology Historical Geology Structure Lab Mineralogy Petrology


Set of metamorphic mineral assemblages, repeatedly associated with each other in space and time.

There is a predictable and common correspondence between the mineralogy of each rock and its bulk chemical composition.

The mineral assemblage defining the metamorphic facies indicates that a state of stable equilibrium has been attained over a restricted P-T condition.

Several different facies have been formally recognized and have names referring to distinct aspects of the facies.

  • e.g. green schist facies = characterized by schists in which green chlorite, talc, serpentine, epidote and actinolite are predominant.

Mineralogical characteristics of the metamorphic facies corresponding to those on the Handout - Facies vs. Grade are:

  1. Zeolite Facies
    • Zeolites are groups of white to colourless hydrous alumina silicates, analogous in composition to feldspars.
    • Laumontite, heulandite and analcine are common, the assemblage Quartz + Laumontite + Chlorite is diagnostic.
  2. Prehnite - Pumpellyite
    • Prehnite +/- Pumpellyite + Quartz is typical.
    • Prehnite - Ca2Al2Si3O10(OH)2 Pumpellyite - Ca2MgAl2(SiO4)(Si2O7)(OH)2H2O
  3. Glaucophane - Lawsonite Schist or Blueschist
    • High P Low T
    • Glaucophane (Na2MgAl2Si8O22(OH)2) (alkali-rich amphibole) + Lawsonite (CaAl2Si2O7(OH)2H2O) are characteristic
    • Jadiete (NaAlSi2O6) + Qtz + Aragonite
  4. Greenschist
    • Albite + Epidote + Actinolite + Chlorite + Calcite in mafic rocks
    • pyrophyllite in pelitic rocks
  5. Amphibolite
    • Hornblende + Plagioclase (An > 20)
    • Kyanite (Al2SiO5) in pelites
  6. Granulite
    • lower crustal lithology
    • cpx + opx + plag + Fe - Mg garnet
  7. Eclogite
    • lower crust or upper mantle lithology
    • Feldspar-free assemblages, with jadiete-rich cpx + pyrope (Mg-rich garnet)

The pressure and temperature range for each facies given in Handout - Facies vs. Grade. The assemblages listed above are mainly for mafic (Metabasite) lithologies. Boundaries between individual facies are not sharp, marked by reactions which occur over a P-T range depending on composition.

All Pages Copyright © GeoClassroom. All Rights Reserved.