Mineral Resources On-Line Spatial Data
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|Name||Coys Hill Porphyritic Granite Gneiss|
|Geologic age||Lower Devonian|
|Original map label||Dchgr|
|Comments||Part of Merrimack Belt (Silurian, Devonian and Pennsylvanian Rocks) Secondary unit description per MA003 as reported in USGS Geologic Names lexicon (ref. MA024): Coys Hill Granite named by Emerson (1898) of Early Devonian age is here renamed Coys Hill Porphyritic Granite Gneiss to more accurately reflect its character in MA. Characterized by variously deformed tabular microcline and locally sodic plagioclase phenocrysts 3 to 10 cm long in a finer matrix of quartz, plagioclase, and biotite with or without muscovite, garnet, and sillimanite (Field, 1975). May be continuous with Cardigan pluton of Kinsman Quartz Monzonite of Billings (1956) (P.J. Thompson, 1983, unpub. data). (Authors note that Kinsman should also be called a granite under current terminology.) Lenses of hornblende-pyroxene gneiss within the Coys Hill unit are mapped separately (Robinson and Luttrell, 1985).|
|Primary rock type||granitic gneiss|
|Secondary rock type|
|Other rock types|
Metamorphic > Gneisscoarse-grained porphyritic microcline granite gneiss, commonly containing garnet and sillimanite with or without muscovite
Unpublished Digital Geologic Map of Massachusetts received from Rudi Hon at Boston College in 1998.
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.
|Geographic coverage||Hampden - Hampshire - Worcester|
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