Sweetheart Mountain Member [of Collinsville Formation]

Gray and silvery (not rusty), medium- to coarse-grained, poorly layered schist, composed of quartz, oligoclase, biotite, muscovite, and garnet, and in places kyanite or sillimanite. Amphibolite layers common; also layers of quartz-spessartine rock (coticule). In the Bristol quad., CT, Collinsville Formation is revised to include a basal unnamed hornblende gneiss member (was upper part of Stanley's (1964) Bristol Member), a middle unnamed metaquartzite member, and the upper Sweetheart Mountain Member. Bristol Member of Stanley (1964) is raised in rank to Bristol Gneiss in the report area. Collinsville unconformably underlies The Straits Schist. Inferred age is Middle Ordovician (Simpson, 1990).
State Connecticut
Name Sweetheart Mountain Member [of Collinsville Formation]
Geologic age Middle Ordovician
Lithologic constituents
Major
Metamorphic > SchistGray and silvery (not rusty), medium- to coarse-grained, poorly layered schist, composed of quartz, oligoclase, biotite, muscovite, and garnet, and in places kyanite or sillimanite.
Minor
Metamorphic > Amphibolite
Incidental
Metamorphiclayers of quartz-spessartine rock (coticule).
Comments Part of Central Lowlands; Iapetus (Oceanic) Terrane - Connecticut Valley Synclinorium; Gneiss Dome Belt, Hawley Formation and equivalent formations (includes Collinsville Formation) (Middle Ordovician). Secondary unit description per CT008.
References

Rodgers, John, compiler, 1985, Bedrock Geological Map of Connecticut: Connecticut Geological and Natural History Survey, Hartford, Connecticut, 2 sheets, scale 1:125,000.

Simpson, H.E., 1990, Bedrock geology of the Bristol quadrangle, Hartford, Litchfield, and New Haven Counties, Connecticut: U.S. Geological Survey Bulletin, 1573, 13 p.

https://pubs.er.usgs.gov/publication/b1573

NGMDB product
Counties Hartford - Litchfield