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Cobble Mountain Formation

Cobble Mountain Formation - Light-brown, fine- to medium-grained pelitic schist and granofels locally graded in beds less than 15 cm thick. Local amphibolite. Rare calc-silicate rock, feldspar gneiss, coticule and cummingtonite schist.
StateMassachusetts
NameCobble Mountain Formation
Geologic ageMiddle Ordovician
Original map labelOca
CommentsPart of Rowe-Hawley Zone (Ordovician and Older Rocks)
Primary rock typepelitic schist
Secondary rock typegranofels
Other rock typesamphibolite; calc-silicate rock; felsic gneiss; schist
Lithologic constituents
Major
Metamorphic > Granoblastic > Granofelsfine- to medium-grained pelitic schist and granofels locally graded in beds less than 15 cm thick; rare cummingtonite schist
Metamorphic > Schistfine- to medium-grained pelitic schist and granofels locally graded in beds less than 15 cm thick; rare cummingtonite schist
Minor
Metamorphic > Amphibolite
Incidental
Metamorphic > Metasedimentary > Calc-silicate-rockcalc-silicate rock
Metamorphic > Gneissfeldspar gneiss
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Unpublished Digital Geologic Map of Massachusetts received from Rudi Hon at Boston College in 1998.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.
Geographic coverageHampden

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