CoachA metamorphic facies is a set of metamorphic mineral assemblages, repeatedly associated in time and space, showing a regular relationship between mineral composition and bulk chemical composition, such that different facies correspond to different metamorphic conditions, chiefly temperature and pressure. The facies are named and defined on the assemblages of rocks of basaltic composition. A facies grid is the arrangement of the facies in the pressure–temperature plane.
| facies | diagnostic minerals of a metabasalt |
|---|---|
| zeolite | zeolites such as laumontite and heulandite |
| prehnite–pumpellyite | prehnite + pumpellyite, prehnite + actinolite, pumpellyite + actinolite |
| greenschist | actinolite + albite + chlorite + epidote |
| epidote amphibolite | hornblende + albite + epidote chlorite |
| amphibolite | hornblende + plagioclase (more than anorthite) |
| granulite | clinopyroxene + orthopyroxene + plagioclase; olivine not stable with plagioclase or garnet |
| blueschist | glaucophane + epidote garnet, or glaucophane + lawsonite |
| eclogite | omphacite + garnet; plagioclase not stable |
| pyroxene hornfels | clinopyroxene + orthopyroxene + plagioclase; olivine stable with plagioclase |
| sanidinite | the same, with very-high-temperature minerals such as pigeonite |
