Stamford Granite Gneiss

White to gray biotite-oligoclase-microcline Rapakivi granite gneiss containing blue quartz. Intrudes Yb, Ybu.
State Massachusetts
Name Stamford Granite Gneiss
Geologic age Proterozoic Y
Lithologic constituents
Major
Metamorphic > GneissWhite to gray biotite-oligoclase-microcline Rapakivi granite gneiss containing blue quartz.
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 Unpublished data from Harding and Mukasa yield a U-Pb zircon date of about 950 Ma per MA011.
References
NGMDB product
Counties Berkshire