Stamford Granite Gneiss (MAYsg;0)

State	Massachusetts
Name	Stamford Granite Gneiss
Geologic age	Proterozoic Y
Original map label	Ysg
Comments	Part of Taconic-Berkshire Zone (Ordovician and Older Rocks) A dike-like feature of Stamford Granite, found near eastern margin of Green Mountain massif near locality 1 on this map (represented by sample 172), was incorrectly referred to as a probable Late Proterozoic diabase dike by Ratcliffe on his section of the Bedrock Map of Massachusetts (Zen and others, 1983). U-Pb zircon dates from Karabinos and Aleinikoff (1988, 1990) yield an age of 959+/-4 Ma. Unpublished data from Harding and Mukasa yield a U-Pb zircon date of about 950 Ma per MA011.
Primary rock type	granitic gneiss
Secondary rock type
Other rock types
Lithologic constituents	Major Metamorphic > GneissWhite to gray biotite-oligoclase-microcline Rapakivi granite gneiss containing blue quartz.
Map references	Unpublished Digital Geologic Map of Massachusetts received from Rudi Hon at Boston College in 1998.
Unit 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., Wones, D.R., 1983, Bedrock Geologic Map of Massachusetts: U.S. Geological Survey, Reston, VA, scale 1: 250,000. Ratcliffe, N.M., Potter, D.B. and Stanley, R.S., 1993, Bedrock geologic map of the Williamstown and North Adams quadrangles, Massachusetts and Vermont, and part of the Cheshire quadrangle, Massachusetts: U.S. Geological Survey Miscellaneous Investigations Series Map, I-2369, 13 p., 2 sheets, scale 1:24,000. [http://pubs.er.usgs.gov/publication/i2369]
Geographic coverage	Berkshire