Brookfield Gneiss (CTOb;0)

Brookfield (dioritic and granodioritic) Gneiss (including Newtown Gneiss of Crowley, 1968) - Dark and light, commonly speckled or banded, medium- to coarse-grained, massive to poorly foliated gneiss, composed of plagioclase, biotite, and hornblende, generally with quartz and K-feldspar, the latter commonly as megacrysts 1 to 3 cm across (also plagioclase megacrysts in darker rocks), locally associated with amphibolite or hornblende schist.

State	Connecticut
Name	Brookfield Gneiss
Geologic age	Middle? Ordovician
Original map label	Ob
Comments	Part of Central Lowlands; Iapetus (Oceanic) Terrane - Connecticut Valley Synclinorium; Newtown Gneiss of Crowley, 1968 (CT008).
Primary rock type	orthogneiss
Secondary rock type	amphibolite
Other rock types	mica schist
Lithologic constituents	Major Metamorphic > Metaigneous > OrthogneissGneiss (dioritic and granodioritic) - Dark and light, commonly speckled or banded, medium- to coarse-grained, massive to poorly foliated gneiss, composed of plagioclase, biotite, and hornblende, generally with quartz and K-feldspar, the latter commonly as megacrysts 1 to 3 cm across (also plagioclase megacrysts in darker rocks). Incidental Metamorphic > Schist > Amphibole-schisthornblende schist Metamorphic > Amphibolite
Map references	Connecticut Geological and Natural History Survey, DEP, in cooperation with the U.S. Geological Survey, 2000, Bedrock Geology of Connecticut, data format: shapefile, file name: bedrock, downloaded from: http://magic.lib.uconn.edu/cgi-bin/MAGIC_DBsearch2.pl?Geography=37800&Loc=0000 on 9/18/2003, scale 1:50,000. [http://magic.lib.uconn.edu/connecticut_data.html#environmental] [http://magic.lib.uconn.edu/cgi-bin/MAGIC_DBsearch2.pl?Geography=37800&Loc=0000]
Unit references	Rodgers, John, compiler, 1985, Bedrock Geological Map of Connecticut: Connecticut Geological and Natural History Survey, Hartford, Connecticut, 2 sheets, scale 125,000.
Geographic coverage	Fairfield - Litchfield - New Haven