Waterford Group - Mamacoke Formation

Light- to dark gray, medium-grained amphibolitic gneiss composed of plagioclase, microcline, quartz, biotite, hornblende, and garnet; locally contains quartz-sillimanite nodules, and thin layers of quartzite and calc-silicate rock.
State Rhode Island
Name Waterford Group - Mamacoke Formation
Geologic age Late Proterozoic? or older?
Lithologic constituents
Major
Metamorphic > GneissLight- to dark gray, medium-grained amphibolitic gneiss composed of plagioclase, microcline, quartz, biotite, hornblende, and garnet.
Incidental
Metamorphic > Metasedimentary > Metaclastic > Quartzitelocally contains quartz-sillimanite nodules, and thin layers of quartzite
Metamorphic > Metasedimentary > Calc-silicate-rock
Comments Part of Hope Valley Subterrane
References

Hermes, O.D. (comp.), Gromet, L.P. (comp.), Murray, D.P. (comp.), Hamidzada, N.A., Skehan, J.W., and Mosher, S., 1994, Bedrock geologic map of Rhode Island: Rhode Island Map Series No. 1, Kingston, Rhode Island, scale 1:100,000.

NGMDB product
Counties Washington