Sterling Igneous Suite - mafic/intermediate gneiss

Gray medium-grained biotite gneiss, commonly with porphyroclasts of microcline/orthoclase, and amphibolite gneiss. Compositions range from quartz diorite to granodiorite. Composed of plagioclase, quartz, microcline/orthoclase, biotite, opaque minerals (commonly as conspicuous magnetite octahedra); accessory apatite, zircon, sphene; secondary chlorite. Varies from massive to layered, with strong penetrative foliation and lineation defined by major minerals. Includes some rock mapped formerly as Blackstone Series in southwestern and westernmost Rhode Island.
State Rhode Island
Name Sterling Igneous Suite - mafic/intermediate gneiss
Geologic age Late Proterozoic
Lithologic constituents
Major
Metamorphic > Gneiss > Biotite-gneissmafic/intermediate gneiss - Gray medium-grained biotite gneiss, commonly with porphyroclasts of microcline/orthoclase, and amphibolite gneiss. Compositions range from quartz diorite to granodiorite. Composed of plagioclase, quartz, microcline/orthoclase, biotite, opaque minerals (commonly as conspicuous magnetite octahedra); accessory apatite, zircon, sphene; secondary chlorite. Varies from massive to layered, with strong penetrative foliation and lineation defined by major minerals.
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 Kent - Washington