Diagnostic minerals in metamorphosed pelitic rocks

Barrovian metamorphism — Regional orogenic metamorphism in the Scottish Highlands

Chlorite zone — slates or phyllites Muscovite (important) Chlorite Biotite (higher-grade part of facies) Pyrophyllite Chloritoid Albite (lower-grade part of facies)

Biotite zone — Slates give way to phyllites or schists Biotite Chlorite Muscovitee Quartz Albite

Garnet zone — Schists with red almandine garnet Garnet Biotite (common) Chlorite Muscovite Quartz Albite or oligoclase

Staurolite zone — Schists Staurolite Biotite Muscovite Quartz Garnet Plagioclase Chlorite (some may persist)

Kyanite zone — Schists Kyanite Biotite Muscovite Quartz Plagioclase Garnet (usually) Staurolite (common)

Sillimanite zone — Schists and gneisses Sillimanite Biotite Muscovite Quartz Plagioclase Garnet Staurolite (maybe) Kyanite (maybe)

Minerals Diagnostic of Different Bulk Compositions in some facies of Regional Metamorphism

NOTE - never are all the minerals listed for a particular bulk composition present together in a single rock. A rock contains some of the many minerals listed. This becomes clear as we consider phase diagrams which apply to metamorphic rocks of restricted composition.

Quartzo-feldspathic rocks are mostly of quartz and feldspar in the greenschist, amphibolite, and pyroxene granulite facies. One or two of the minerals listed for mafic or calcareous or pelitic rocks in the appropriate facies may also be present.

Symbols used: (mineral) = rare or minor constituent CAPITALIZED mineral helps distinguish rocks from next-lower-grade facies

GREENSCHIST FACIES

Mafic Rocks Calcareous Rocks Pelitic Rocks chlorite calcite muscovite (IMPORTANT) epidote group dolomite quartz calcite ankerite chlorite albite siderite (lower-grade GS-facies) biotite (higher-grade GS-facies) actinolite (higher-grade GS-facies) epidote group pyrophyllite (biotite) quartz chloritoid (quartz) Mg-chlorite (albite) (muscovite (lower-grade GS-facies)) (talc)

Magnesian Rocks Talc; antigorite [= serpentine]; tremolite-actinolite; brucite; magnesite; chlorite

EPIDOTE AMPHIBOLITE FACIES

Mafic Rocks Calcareous Rocks Pelitic Rocks chlorite calcite muscovite (IMPORTANT) epidote group dolomite (but not with quartz) quartz calcite epidote group chlorite (Mg-rich) plagioclase quartz biotite (biotite) TREMOLITE ALMANDINE-spessartine (quartz) Mg-chlorite chloritoid HORNBLENDE or actinolite (plagioclase) pyrophyllite almandine-pyrope (phlogopite) (plagioclase)

Magnesian Rocks Talc; antigorite [= serpentine]; tremolite-actinolite; brucite; magnesite; (chlorite) AMPHIBOLITE FACIES

Mafic Rocks Calcareous Rocks Pelitic Rocks intermediate plagioclase calcite muscovite (IMPORTANT - not at high grade) hornblende dolomite (but not with quartz) quartz anthophyllite hornblende or tremolite biotite cummingtonite epidote group (low-grade A-facies) almandine epidote group (low-grade A- intermed.- or Ca-plagioclase STAUROLITE facies) almandine-pyrope diopside KYANITE or ANDALUSITE diopside forsterite (high-grade A-facies) sillimanite (high-grade A-facies) (quartz) (phlogopite ) K-feldspar-sillimanite (high-grade A-facies) (cordierite) (Mg chlorite) (low-grade A-facies) cordierite (biotite) grossularite-andradite (plagioclase) (sphene) (very-Mg-rich chlorite) (low-grade A-facies)

Magnesian Rocks Anthophyllite; actinolite; olivine

PYROXENE GRANULITE FACIES

Mafic Rocks Calcareous Rocks Pelitic Rocks intermediate plagioclase calcite quartz AUGITE or diopside dolomite ( but not with quartz) sillimanite ENSTATITE diopside (kyanite) almandine-pyrope forsterite almandine olivine quartz orthoclase anthophyllite or cummingtonite (low-grade G- grossularite-andradite cordierite (low-grade facies) G-facies) (quartz) calcic plagioclase (plagioclase) wollastonite (high-grade G-facies) ENSTATITE

Magnesian Rocks Anthophyllite or cummingtonite (low-grade G-facies); olivine; ENSTATITE

BLUESCHIST FACIES

Mafic Rocks Calcareous Rocks Pelitic Rocks glaucophane ARAGONITE or calcite (low-grade muscovite BS-facies) impure jadeite dolomite quartz LAWSONITE quartz stilpnomelane almandine glaucophane chlorite pumpellyite (LAWSONITE) glaucophane aragonite or calcite (low-grade BS- pumpellyite almandine facies) albite (low-grade BS-facies) chlorite (quartz)

Quartzo-Feldspathic Rocks (generally derived from graywacke or arkosic arenite) Quartz; jadeite (high-grade BS-facies); LAWSONITE; glaucophane; stilpnomelane; (muscovite); albite (low-grade BS-facies); (ARAGONITE or calcite (low-grade BS-facies))