Geologic units containing Mafic gneiss

Mafic gneiss
A gneissic rock dominated by dark-colored minerals, commonly biotite and hornblende

Alabama - Colorado - Connecticut - Georgia - Idaho - Massachusetts - North Carolina - New York - Pennsylvania - Rhode Island - South Carolina - Virginia - Vermont

Alabama

Colorado

Connecticut

Amphibolite unit [in Ratlum Mountain Schist] (Lower? Ordovician)
Amphibolite unit [in Ratlum Mountain Schist] - Black or mottled, generally massive amphibolite and hornblende gneiss, composed of hornblende and andesine, commonly with minor quartz and magnetite, and locally with garnet, biotite, and epidote.
Dioritic phase [of Lebanon Gabbro] (Devonian)
Dioritic phase [of Lebanon Gabbro] - White to black, streaked, medium-grained, foliated or sheared gneiss, composed of plagioclase, biotite, quartz, and generally hornblende.
Foliated quartz diorite (Devonian in part, probably Ordovician in part)
Foliated quartz diorite - Mainly dark-gray, medium-grained, well-foliated gneiss (locally strongly sheared, especially near contacts), composed of plagioclase, quartz, biotite, and hornblende, locally also pyroxene.
Hornblende gneiss member [of Collinsville Formation] (Middle Ordovician)
Hornblende gneiss member [of Collinsville Formation] - Dark, fine- to medium-grained, well-layered amphibolite and hornblende gneiss, composed of hornblende and plagioclase, commonly with biotite, garnet, or epidote, interlayered with light-gray felsic gneiss and pink quartz-spessartine rock (coticule). Grades into Bristol Gneiss.
Lower member [of Middletown Formation] (Middle Ordovician)
Lower member [of Middletown Formation] - Dark- to medium-gray amphibolite and hornblende gneiss, commonly with garnet, diopside, or epidote, interlayered with light-gray gneiss composed of oligoclase, quartz, biotite, and generally one or more amphiboles, also garnet.
Middletown Formation (Middle Ordovician)
Middletown Formation ( = Ammonoosuc Volcanics of New Hampshire) - Heterogeneously interlayered dark- to light-gray, generally medium grained gneiss and granofels, ranging from quartz-biotite gneiss through felsic amphibole gneiss to amphibolite and characteristically containing anthophyllite or cummingtonite with or without hornblende. Also layers of calc-silicate rock and of biotite gneiss with quartz-sillimanite nodules.
Middletown Formation (Middle Ordovician)
Middletown Formation ( = Ammonoosuc Volcanics of New Hampshire) - Heterogeneously interlayered dark- to light-gray, generally medium grained gneiss and granofels, ranging from quartz-biotite gneiss through felsic amphibole gneiss to amphibolite and characteristically containing anthophyllite or cummingtonite with or without hornblende. Also layers of calc-silicate rock and of biotite gneiss with quartz-sillimanite nodules.
Quinebaug Formation (Middle Ordovician or older)
Quinebaug Formation - Medium- to dark-gray, commonly greenish, medium-grained, well-layered gneiss, composed of hornblende, andesine, biotite, and epidote, commonly with quartz or garnet, interlayered with amphibolite.
Ratlum Mountain Schist plus Amphibolite unit [in Ratlum Mountain Schist] (Lower Ordovician)
Ratlum Mountain Schist plus Amphibolite unit [in Ratlum Mountain Schist] - Ratlum Mountain Schist - Gray, medium-grained, interlayered schist and granofels, composed of quartz, oligoclase, muscovite (in the schist), biotite, and garnet, also staurolite and kyanite in the schist. Numerous layers and lenses of amphibolite; also some of quartz-spessartine (coticule) and calc-silicate rock. Amphibolite unit [in Ratlum Mountain Schist] (Lower? Ordovician) - Black or mottled, generally massive amphibolite and hornblende gneiss, composed of hornblende and andesine, commonly with minor quartz and magnetite, and locally with garnet, biotite, and epidote.
Rowe Schist plus Amphibolite unit [in Rowe Schist] (Lower Ordovician or Cambrian or both)
Rowe Schist plus Amphibolite unit [in Rowe Schist] - Rowe Schist - Light-gray to silvery, fine- to medium-grained, generally poorly layered schist, composed of quartz, muscovite, biotite, oligoclase, and generally garnet, staurolite, and kyanite or sillimanite. Layers of granofels common; also some layers of amphibolite, quartz-spessartine rock (coticule), and calc-silicate rock. Amphibolite unit [in Rowe Schist] - Black or mottled, generally massive amphibolite and hornblende gneiss, composed of hornblende and andesine.

Georgia

Idaho

Massachusetts

Black and white, well-layered hornblende-biotite-plagioclase gneiss and amphibolite (Proterozoic Y)
Black and white, well-layered hornblende-biotite-plagioclase gneiss and amphibolite - Contains irregular pods of diopside or cummingtonite-talc rock or amphibole calc-silicate, epidote-layered quartz-plagioclase gneiss near Hinsdale.
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.
Coys Hill Porphyritic Granite Gneiss (Lower Devonian)
Coys Hill Porphyritic Granite Gneiss - Hornblende gneiss inclusions in granitic gneiss of the Coys Hill.
Diorite (Proterozoic Z)
Diorite - Medium-grained hornblende diorite metamorphosed in part to amphibolite and hornblende gneiss.
Gabbro (Proterozoic Z)
Gabbro - Hornblende gabbro and hornblende-pyroxene gabbro metamorphosed in part to hornblende gneiss and amphibolite.
Gneiss and schist near New Bedford (Proterozoic Z)
Gneiss and schist near New Bedford - Hornblende and biotite schist and gneiss, amphibolite.
Hornblende-plagioclase gneiss (Precambrian to Paleozoic)
Hornblende-plagioclase gneiss .
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.
Lee Gneiss (Proterozoic Y)
Lee Gneiss - Hornblende-spotted plagioclase-hornblende-quartz gneiss and granofels and well-layered biotite-hornblende-plagioclase-quartz gneiss containing knots of diopside or epidote.
Littleton Formation (Lower Devonian)
Littleton Formation - Orthopyroxene-biotite gneiss, probably originally intermediate volcanic rocks.
Partridge Formation (Middle Ordovician)
Partridge Formation (includes Brimfield Schist of Emerson, 1917) - Mafic and felsic gneisses of volcanic derivation with calc-silicate granofels.
Quinebaug Formation (Ordovician, Cambrian, or Proterozoic Z)
Quinebaug Gneiss - Amphibolite, biotite and hornblende gneiss, felsic gneiss, and calc-silicate gneiss.
Washington Gneiss (Proterozoic Y)
Washington Gneiss - Coarse- to medium-grained hornblende-garnet amphibolite, hornblende-plagioclase gneiss and phlogopite-hornblende-plagioclase amphibolite (metabasalt).
Well-layered hornblende-biotite gneiss (Proterozoic Y)
Well-layered hornblende-biotite gneiss .

North Carolina

New York

Pennsylvania

Banded mafic gneiss (Precambrian)
Banded mafic gneiss - Dark, fine to medium grained; includes rocks of probable sedimentary origin; may be equivalent to "PZmgh."
Felsic and intermediate gneiss (Precambrian)
Felsic and intermediate 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.
"Glenarm Wissahickon" formation (Probably lower Paleozoic)
"Glenarm Wissahickon" formation - Lithologically similar to oligoclase-mica schist of the Wissahickon Formation (PZw), but also includes lenticular amphibolite bodies having ocean-floor basalt chemistry.
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.
Hornblende gneiss (Precambrian)
Hornblende gneiss - Dark, medium grained; includes some rocks of probable sedimentary origin.
Mafic gneiss (Probably lower Paleozoic)
Mafic gneiss - Dark, medium grained; includes rocks of probable sedimentary origin; may be equivalent to pCAmgp in places.
Mafic gneiss (Precambrian)
Mafic gneiss - Dark, medium grained; includes rocks of probable sedimentary origin; may be equivalent to "PZmgh" in places.
Mafic gneiss (Precambrian)
Mafic gneiss - Dark, medium grained; includes rocks of probable sedimentary origin; may be equivalent to "PZmgp" in places.
Mafic gneiss (Probably lower Paleozoic)
Mafic gneiss - Dark, medium grained; includes rocks of probable sedimentary origin; may be equivalent to pCAmgh in places.
Metagabbro (Probably lower Paleozoic)
Metagabbro - Ranges from fine- to medium-grained, altered gabbro to hornblende gneiss.
Wissahickon Formation (Probably lower Paleozoic)
Wissahickon Formation - Includes oligoclase-mica schist, some hornblende gneiss, some augen gneiss, and some quartz-rich and feldspar-rich members due to various degrees of granitization.

Rhode Island

South Carolina

Virginia

Vermont

Missisquoi Formation, Barnard Volcanic Member (Ordovician)
Missisquoi Formation, Barnard Volcanic Member - Fine- to medium-grained biotite gneiss, hornblende gneiss, and amphibolite.
Mount Holly Complex (Precambrian)
Mount Holly Complex - Mainly fine- to medium-grained biotitic gneiss, locally muscovitic, and in western areas chloritic; massive and granitoid in some localities, fine-grained or schistose and compositionally layered in others; also abundant amphibolite and hornblende gneiss, and minor beds of mica schist, quartzite, and calc-silicate granulite; includes numerous small bodies of pegmatite and gneissoid granitic rock. Includes a suite of metatonalites, metatrondhjemite, and possible metadacite with chemical characteristics of a calc-alkaline volcanic-plutonic suite. Mappable units are College Hill Granite Gneiss and 10 unnamed subdivisions including several varieties of gneiss as well as schist, amphibolite, and quartzite. U-Pb zircon upper intercept ages of 1.35 to 1.30 Ga have been determined and interpreted as age of crystallization (Ratcliffe and others, unpub. data). Cores of abraded zircon obtained from College Hill Granite Gneiss of Mount Holly Complex have a U-Pb upper intercept age of 1245 +/-14 Ma, interpreted as crystallization age for that granite (Aleinikoff and others, 1990). Dust collected by abrasion of zircons, thought to represent migmatitic overgrowth, has a Pb-Pb age of approx 1100 Ma. These data suggest that College Hill Granite Gneiss was intruded at 1245 Ma and migmatized at 1100 Ma. On north and south slopes of College Hill, College Hill Granite Gneiss grades outward into migmatitic biotite granite gneiss of Mount Holly Complex. College Hill is discordant to contacts and folds in paragneiss units of Mount Holly Complex. Dacitic metavolcanics are found within Washington Gneiss of Berkshire massif of MA (Ratcliffe and Zartman, 1968). They are interbedded with thick succession of rusty-weathering, quartz-pebble gneisses, calc-silicate rocks and garnet-sillimanite schist similar to, but much thicker than, the rusty-weathering gneiss and schist unit of Mount Holly Complex exposed in Green Mountains of VT. It is possible that the metadacitic and metatrondhjemitic suite of VT constitutes a lateral, south-to-north facies of the Washington Gneiss of MA (Ratcliffe, in press).
Mount Holly Complex, quartzite and schist (Precambrian)
Mount Holly Complex, quartzite and schist - Quartzite, locally in massive beds as much as 30 ft thick, micaceous quartzite, and quartz-mica schist that commonly contains garnet or pseudomorphs (largely chlorite) after garnet; schists are locally rusty weathered and contain conspicuous flakes of graphite; also includes amphibolite and minor hornblende gneiss, biotite gneiss, and pegmatite.