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Interstate 84 and state Route 172 interchange, Southbury, New Haven Co., Connecticut, USA

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Lock Map
Latitude & Longitude (WGS84): 41° 28' 39'' North , 73° 12' 30'' West
Latitude & Longitude (decimal): 41.47750,-73.20833
GeoHash:G#: dr7gynerf
Köppen climate type:Cfa : Humid subtropical climate

According to Hiller (1967), pyrrhotite was exposed in the rock cut on the eastbound ramp onto I-84.

Mineral List

1 valid mineral.

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on

Ordovician - Neoproterozoic
443.8 - 1000 Ma

ID: 3190671
Precambrian-Phanerozoic sedimentary rocks

Age: Neoproterozoic to Ordovician (443.8 - 1000 Ma)

Lithology: Mudstone-carbonate-sandstone-conglomerate

Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529. [154]

Middle Ordovician
458.4 - 470 Ma

ID: 2907888
Collinsville Formation

Age: Middle Ordovician (458.4 - 470 Ma)

Stratigraphic Name: Collinsville Formation

Description: Mixture of rock types as described for the two members; in many areas felsic and mafic striped metavolcanic rocks predominate.

Comments: Part of Central Lowlands; Iapetus (Oceanic) Terrane - Connecticut Valley Synclinorium; Gneiss Dome Belt. Hawley Formation and equivalent formations (includes Collinsville Formation) (Middle Ordovician). Two members referred to in primary description are units: Ocs and Ocg. Secondary unit description per CT008. Secondary unit description from USGS Geologic Names lexicon (ref. CT017): Metamorphic strata in the report area that lie above the Bristol Gneiss (as it is here revised) and below The Straits Schist are assigned to the Collinsville Formation. Unit is divided into a lower unnamed hornblende gneiss member (was uppermost part of Stanley's (1964) Bristol Member) approximately 400 ft thick, an unnamed metaquartzite member that averages 100 ft, and the upper Sweetheart Mountain Member adopted here as defined by Stanley. Inferred age is Middle Ordovician. Correlates, at least in part, with the Hawley Formation of MA (Simpson, 1990). Also from ref. CT017: Part of Bronson Hill anticlinorium, not part of Rowe-Hawley zone, but discussed in this report to emphasize importance of junction between Rowe-Hawley zone and Bronson Hill anticlinorium. Collinsville is exposed in Granville and Shelburne Falls domes, and to a limited extent in Goshen dome (Hatch and Warren, 1982). Consists of various light-colored, plagioclase-rich gneisses and interlayered amphibolite and hornblende gneiss. Upper part is amphibolite-rich; lower part is predominantly feldspathic gneiss. In places, thin aluminous feldspathic schist, locally containing coticule and amphibolite, forms an upper unnamed member of formation in Granville dome, or is Sweetheart Mountain Member of Stanley (1964) in Collinsville and Bristol domes in CT. Most complete sequence is in Shelburne Falls dome where L.M. Hall (1977, written commun.) has recognized seven mappable subdivisions. With minor modification, they are (ascending) 1) amphibolite with thin felsic gneiss layers; 2) rusty-weathering massive granulites; 3) very homogeneous garnetiferous biotite gneiss; 4) interlayered amphibolite and felsic gneiss; 5) felsic gneiss with scattered biotite +/-magnetite, garnet, and hornblende; 6) interbedded amphibolite and white felsic gneiss; and 7) gray, tan-weathering granulites containing thin coticule layers. Members 4, 5 and 6 are approximately equivalent to Ammonoosuc Volcanics. Member 3 is lithically similar to Monson and Fourmile Gneisses. Age in report is Ordovician. [Papers presented as chapters in U.S. Geological Survey Professional Paper 1366 are intended as explanations and (or) revisions to MA State bedrock geologic map of Zen and others (1983) at scale of 1:250,000.]

Lithology: Major:{gneiss,amphibolite}, Minor:{metavolcanic}, Incidental:{granulite}

Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052. [133]

Data and map coding provided by, used under Creative Commons Attribution 4.0 License

This page contains all mineral locality references listed on This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.


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Hiller, John. (1967), unpublished sketch map.

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