Geologic units containing felsic gneiss

Earth material > Metamorphic rock > Gneiss

Felsic gneiss

A gneissic rock dominated by light-colored minerals, commonly quartz and feldspar

Alabama - Colorado - Connecticut - Georgia - Idaho - Massachusetts - Maine - North Carolina - New Hampshire - New Mexico - New York - Pennsylvania - Rhode Island - Virginia

Alabama

Hatchet Creek Group; Pinchoulee Gneiss (Precambrian to Paleozoic): Pinchoulee Gneiss - medium to fine-grained migmatitic, locally garnetiferous biotite-feldspar gneiss, commonly saturated with granitic pods.
Higgins Ferry Group (Precambrian to Paleozoic): Higgins Ferry Group - thinly layered coarse to fine-grained biotite-feldspar-quartz gneiss, sericite-feldspar-muscovite schist, +/- biotite +/- garnet-muscovite schist, and biotite-garnet feldspathic gneiss; locally common pegmatites.
Mad Indian Group (Precambrian to Paleozoic): Mad Indian Group - fine-grained feldspathic biotite gneiss; medium to coarse-grained muscovite-biotite-garnet schist; locally kyanite and sillimanite. Many of the schists have been retrograded to chlorite-garnet-quartz-sericite schist. Both mi and migr extensively cut by feldspathic dikes and pegmatites.
Motts Gneiss (Precambrian to Paleozoic): Motts Gneiss - leucocratic quartz-rich quartz diorite pencil gneiss.
Opelika Complex; Auburn Gneiss (Precambrian to Paleozoic): Auburn Gneiss - fine-grained biotite-oligoclase gneiss intermixed with coarse-grained muscovite-biotite schist; locally contains muscovite-rich pegmatite.
Uchee Complex; Phenix City Gneiss (Precambrian to Paleozoic): Phenix City Gneiss - biotite-epidote quartz diorite gneiss and biotite-hornblende gneiss; locally includes migmatitic amphibolite; cut by numerous granitic veins.
Wedowee Group; Wedowee Group undifferentiated (Precambrian to Paleozoic): Wedowee Group undifferentiated - Wedowee Group undifferentiated includes the Cragford Phyllite and Cutnose Gneiss. Cragford Phyllite -- interbedded fine-grained graphite-chlorite-sericite schist and phyllite, garnet-sericite schist and phyllite, graphite-quartz-sericite phyllite, locally feldspathic biotite gneiss, calc-silicate rock, and quartzite. Cutnose Gneiss -- cyclically interbedded fine-grained quartz-biotite feldspathic gneiss, graphite-chlorite-sericite schist, locally thin interbeds of graphite-quartz-sericite phyllite, and quartzite. Rocks in the area northeast of Clanton in Chilton and Coosa Counties that are here assigned to the Wedowee Group also have been interpreted as part of the Higgins Ferry Group.

Colorado

Felsic and hornblendic gneisses, either separate or interlayered (Proterozoic | Paleoproterozoic): Includes metabasalt, metatuff, and interbedded metagraywacke; locally contains interlayered biotite gneiss. Derived principally from volcanic rocks

Connecticut

Felsic gneiss member [of Quinebaug Formation] (Middle Ordovician or older): Felsic gneiss member [of Quinebaug Formation] - Light- to medium-gray, fine- to medium-grained gneiss, composed of plagioclase, quartz, biotite, and muscovite, commonly with K-feldspar.
Hornblende gneiss and amphibolite (Proterozoic Y): Hornblende gneiss and amphibolite - Dark-gray to mottled, fine- to medium-grained, massive to foliated amphibolite and gneiss, composed of hornblende and plagioclase, also commonly biotite and minor quartz; commonly interlayered with banded felsic gneiss. Locally contains calc-silicate rock or diopsidic calcite marble.

Georgia

Biotite Gneiss/ Feldspathic Biotite Gneiss (Precambrian-Paleozoic): Biotite Gneiss/ Feldspathic Biotite Gneiss

Idaho

Felsic gneiss, mafic gneiss, orthogneiss, and calc-silicate rock; Early Proterozoic metamorphic rocks; central Idaho; Pioneer Mountains metamorphic core complex (Early Proterozoic): Precambrian, high-grade metamorphic rock; metasediment subdivisions are (PC3, PC2, PC1).

Massachusetts

Ammonoosuc Volcanics (Middle Ordovician): Ammonoosuc Volcanics - Amphibolite, felsic gneiss, garnet-amphibole quartzite, and marble too thin to show separately at map scale. Gedrite, anthophyllite, cummingtonite locally abundant in amphibolite layers.
Cobble Mountain Formation (Middle Ordovician): Cobble Mountain Formation - Light-brown, fine- to medium-grained pelitic schist and granofels locally graded in beds less than 15 cm thick. Local amphibolite. Rare calc-silicate rock, feldspar gneiss, coticule and cummingtonite schist.
Collinsville Formation (Middle Ordovician or older): Collinsville Formation - Interlayered amphibolite and white felsic gneiss containing biotite, hornblende, and magnetite. Local calc-silicate beds. Coticule-bearing granofels, muscovite quartzite and amphibolite in upper part.
Collinsville Formation (Middle Ordovician or older): Collinsville Formation - Interlayered amphibolite and felsic gneiss in beds less than 1 m thick. Local, coarse-grained magnetite-hornblende gneiss.
Collinsville Formation (Middle Ordovician or older): Collinsville Formation - Amphibolite, locally very garnetiferous, containing beds of felsic gneiss.
Collinsville Formation (Middle Ordovician or older): Collinsville Formation - Felsic gneiss containing scattered biotite, magnetite, garnet and hornblende. Local beds of amphibolite.
Intimately interfolded Littleton and Partridge Formations (Lower Devonian and Middle Ordovician): Intimately interfolded Littleton and Partridge Formations - In areas of poor exposure and incomplete mapping.
Littleton Formation (Lower Devonian): Littleton Formation - Quartz-feldspar-garnet gneiss, probably originally felsic volcanic rocks.
Partridge Formation (Middle Ordovician): Partridge Formation (includes Brimfield Schist of Emerson, 1917) - Layered felsic gneiss and schist.
Partridge Formation (Middle Ordovician): Partridge Formation (includes Brimfield Schist of Emerson, 1917) - Mafic and felsic gneisses of volcanic derivation with calc-silicate granofels.
Partridge Formation (Middle Ordovician): Partridge Formation (includes Brimfield Schist of Emerson, 1917) - Felsic gneiss of volcanic derivation and minor amphibolite.
Pinkish-gray, fine-grained, well-laminated felsic biotite-microcline-plagioclase-quartz gneiss (Proterozoic Y): Pinkish-gray, fine-grained, well-laminated felsic biotite-microcline-plagioclase-quartz gneiss - Probably metamorphosed rhyolite.
Quinebaug Formation (Ordovician, Cambrian, or Proterozoic Z): Quinebaug Gneiss - Amphibolite, biotite and hornblende gneiss, felsic gneiss, and calc-silicate gneiss.

Maine

Precambrian gneisses of the Chain Lakes Massif (Precambrian): Precambrian gneisses of the Chain Lakes Massif

North Carolina

Felsic Mica Gneiss (Cambrian/Late Proterozoic): Felsic Mica Gneiss - interlayered with graphitic mica schist and mica-garnet schist, commonly with kyanite; minor hornblende gneiss.
Felsic Mica Gneiss (Cambrian/Late Proterozoic): Felsic Mica Gneiss - interlayered with biotite and hornblende gneiss and schist.
Lineated Felsic Mica Gneiss (Cambrian/Late Proterozoic): Lineated Felsic Mica Gneiss - white to pink, with strong lineation of muscovite-biotite streaks and prismatic quartz aggregates; planar foliation and layering weak; minor mica schist and hornblende gneiss.

New Hampshire

Massabesic Gneiss Complex (Late Proterozoic): Massabesic Gneiss Complex - Quartzose-feldspathic gneiss and biotite schists (locally rusty), granofels, and cal-silicate rocks closely intruded by, and grading into, a pink gneissic granite (623 Ma) that produced a migmatite.

New Mexico

metamorphic rocks (Proterozoic | Paleoproterozoic): Lower Proterozoic metamorphic rocks, dominantly felsic volcanic, volcaniclastic and plutonic rocks (1650-1700+ Ma); includes Vadito Group; locally includes high-grade felsic gneisses of unknown age

New York

Charnockite, granitic and quartz syenite gneiss (Middle Proterozoic): Charnockite, granitic and quartz syenite gneiss - variably leucocratic, containing varying amounts of hornblende, pyroxenes, biotite; may contain interlayered amphibolite, metasedimentary gneiss, migmatite. Overprint signifies inequigranular texture or phacoidal structure.
Charnockite, granitic and quartz syenite gneiss (Middle Proterozoic): Charnockite, granitic and quartz syenite gneiss - variably leucocratic, containing varying amounts of hornblende, pyroxenes, biotite; may contain interlayered amphibolite, metasedimentary gneiss, migmatite. Overprint signifies inequigranular texture or phacoidal structure.
Quartz-feldspar gneiss (Middle Proterozoic): Quartz-feldspar gneiss - with variable amounts of garnet, sillimanite, biotite.
Quartz-feldspar gneiss (Middle Proterozoic): Quartz-feldspar gneiss - with variable amounts of garnet, sillimanite, biotite.

Pennsylvania

Felsic and intermediate gneiss (Precambrian): Felsic and intermediate gneiss - Light, medium grained; includes rocks of probable sedimentary origin.
Felsic and intermediate gneiss (Precambrian): Felsic and intermediate gneiss - Medium grained, light pink to greenish gray; largely quartz, feldspar, and mica; commonly gneissic, containing alteration minerals; interfingers with gabbroic gneiss.
Felsic gneiss (Precambrian): Felsic gneiss - Light, medium grained; includes rocks of probable sedimentary origin.
Felsic to mafic gneiss (Precambrian): Felsic to mafic gneiss - Light, medium grained; predominantly quartz and feldspar of igneous origin.
Graphitic felsic gneiss (Precambrian): Graphitic felsic gneiss - Medium grained, medium to dark gray; locally gneissic, predominantly feldspar and quartz, plus dark accessories and various alteration minerals.

Rhode Island

Harmony Group - Woonasquatucket Formation (Late Proterozoic? or older?): Harmony Group - Woonasquatucket Formation - Gray, medium-grained felsic gneiss, composed of microcline-microperthite, quartz, albite, muscovite, and biotite. Commonly phyllonitic.

Virginia

Lake Jackson Pluton (Ordovician): Lake Jackson Pluton - Micaceous metatonalite.
Layered Quartzofeldspathic Augen Gneiss and Flaser Gneiss (Proterozoic Y): Layered quartzofeldspathic augen gneiss and flaser gneiss.
Metatonalite (Ordovician): Metatonalite
Quartzofeldspathic Gneiss (Proterozoic Y-Pennsylvanian): Quartzofeldspathic gneiss

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