|Geologic age||Cambro-Ordovician? to Carboniferous?|
Igneous > Hypabyssal > Lamprophyre (Dike or sill)minette - Olive-gray to pale-gray, 1- to 4-m-wide dikes, mostly massive and porphyritic, but locally schistose, composed of biotite phenocrysts in a fine-grained groundmass of microcline, plagioclase, and quartz. Contains accessory apatite and pyrite, and secondary chlorite, sericite, calcite, and opaque minerals.
|Comments||Part of Esmond-Dedham Subterrane (East Bay Area). Printed map unit symbol is OCm, digital is OCmn.|
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.