Mamacoke Formation (CTZwm;0)

Mamacoke Formation - Interlayered (but layers locally indistinct) light- to dark-gray, medium-grained gneiss, composed of plagioclase, quartz, and biotite; sillimanite, garnet, hornblende, or microcline in certain layers; in upper part locally contains quartz-sillimanite nodules or thin layers of quartzite, amphibolite, or calc-silicate rock.

State	Connecticut
Name	Mamacoke Formation
Geologic age	Proterozoic Z?
Original map label	Zwm
Comments	Part of Eastern Uplands; Avalonian (Continental) Terrane; Avalonian Anticlinorium
Primary rock type	gneiss
Secondary rock type	quartzite
Other rock types	amphibolite; calc-silicate rock
Lithologic constituents	Major Metamorphic > GneissInterlayered (but layers locally indistinct) light- to dark-gray, medium-grained gneiss, composed of plagioclase, quartz, and biotite; sillimanite, garnet, hornblende, or microcline in certain layers. Incidental Metamorphic > Metasedimentary > Calc-silicate-rockcalc-silicate rock in upper part Metamorphic > Amphibolitein upper part Metamorphic > Metasedimentary > Metaclastic > Quartzitein upper part locally contains quartz-sillimanite nodules or thin layers of quartzite
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	Middlesex - New London