Dark-gray to greenish-black, fine-grained lamprophyre dikes, with flow-banding parallel to contacts; contains microphenocrysts of titaniferous augite, olivine, kaersutite, phlogopite, apatite, and opaque minerals enclosed in a matrix of analcite and calcite; ocellar texture locally developed. Locally abundant megacrysts (up to 5 cm) of pyroxene, and rounded xenoliths (up to 8 cm) composed of olivine, enstatite, chrome-diopside, and chrome-spinel.
State Rhode Island
Name monchiquite
Geologic age Jurassic
Lithologic constituents
Igneous > Hypabyssal > Lamprophyre (Dike or sill)
Comments Part of Avalon Terrane. Per printed map: age of rock based on radiometric data from RI006.

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.

Hermes, O.D., Rao, J.M., Dickenson, M.P., and Pierce, T.A., 1984, A transitional alkalic dolerite dike suite of Mesozoic age in southeastern New England: Contributions to Mineralogy and Petrology, v. 86, p. 386-397.

NGMDB product
Counties Washington