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 Facie
s
• 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

also
• 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)