Partridge Formation (includes Brimfield Schist of Emerson, 1917)

Sulfidic mica schist and subordinate amphibolite.
State Massachusetts
Name Partridge Formation (includes Brimfield Schist of Emerson, 1917)
Geologic age Middle Ordovician
Lithologic constituents
Major
Metamorphic > Schist > Mica-schistsulfidic mica schist
Minor
Metamorphic > Amphibolitesubordinate amphibolite
Comments Part of Bronson Hill Zone (Ordovician and Older Rocks). U-Pb zircon ages suggest that the Ammonoosuc Volcanics and tuffs of the Partridge Formation were erupted between 453 to 449 Ma, meaning they are of late Middle Ordovician and earliest Late Ordovician age. The stratigraphic relationships of these two units is very complex with current thought being that the Partridge lies between the lower and upper members of the Ammonoosuc Volcanics (Tucker and Robinson, 1990) per MA015.
References

Zen, E-An (ed.), Goldsmith, R. (comp.), Ratcliffe, N.M. (comp.), Robinson, P. (comp.), Stanley, R.S. (comp.), Hatch, N.L., Jr., Shride, A.F., Weed, E.G.A., and Wones, D.R., 1983, Bedrock Geologic Map of Massachusetts: U.S. Geological Survey, Reston, VA, scale 1: 250,000.

https://pubs.er.usgs.gov/publication/70046713

Tucker, R.D. and Robinson, Peter, 1990, Age and setting of the Bronson Hill magmatic arc; a re-evaluation based on U-Pb zircon ages in southern New England: Geological Society of America Bulletin, v. 102, no. 10, p. 1404-1419.

NGMDB product
Counties Franklin - Hampden - Hampshire - Worcester