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Gloucester, Essex Co., Massachusetts, USA

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Latitude & Longitude (WGS84): 42° 36' 57'' North , 70° 39' 43'' West
Latitude & Longitude (decimal): 42.6158333333, -70.6619444444

A populated place (city) on Cape Ann.

Area granite quarries and other bedrock exposures. Plutonic rocks of Cape Ann include gabbro, foidal syenite, alkali-feldspar syenite and alkali-feldspar granite. Pegmatites and miarolitic cavities are associated with the granite.

Mineral List

Mineral list contains entries from the region specified including sub-localities

Regional Geology

Permian - Carboniferous252.17 - 358.9 MaCarboniferous-Permian sedimentary rocks

Sedimentary rocks

Wenlock - Late Ordovician427.4 - 458.4 MaCape Ann Complex

Major:: {alkali-granite (alaskite)},Minor:: {quartz syenite}

Cape Ann Complex - Alkalic granite to quartz syenite containing ferro-hornblende. Intrudes Zdigb. Most of Cape Ann Complex forms Cape Ann peninsula of northeastern MA. Consists of alkalic granite to quartz syenite (its main phase), Beverly Syenite, and Squam Granite, all of which form a pluton covering 385 sq km. Intrudes Late Proterozoic greenschist, diorite, and gabbro that earlier workers assigned to Marlboro Formation, Salem Gabbro-Diorite, or Middlesex Fells Volcanic Complex. Dennen (1975) considered masses of diorite and gabbro within and adjacent to Cape Ann Complex to be cogenetic with it and equivalent in age to Nahant Gabbro and gabbro at Salem Neck. Authors recommend that usage of term Salem Gabbro-Diorite be restricted to these masses of diorite and gabbro in and around Cape Ann pluton that are younger than Dedham Granite and cogenetic with Cape Ann Complex. Gabbro at Salem Neck is probably representative. Radiometric ages straddle Late Ordovician-Early Silurian boundary. Age is based on Rb-Sr whole rock isochron of 426 +/-6 Ma (Zartman and Marvin, 1971) and U-Pb zircon date of 450 +/-25 Ma (Zartman, 1977) (Wones and Goldsmith, 1991).

Part of Milford-Dedham Zone (Tertiary and Older Rocks) Secondary unit description per MA007.

References for regional geology:

Data provided by

USGS compilers. State geologic map data. State Maps.

Geological Survey of Canada. Generalized geological map of the world and linked databases. doi:10.4095/195142. Open File 2915d.

48 valid minerals.

Localities in this Region

The above list contains all mineral locality references listed on This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.


Cooke, Josiah P., Jr. (1866): On Danalite, a new Mineral Species from the Granite of Rockport, Mass. (American Journal of Science and Arts 47:73-78).

Shaler, N. S. (1888): The Geology of Cape Ann, Massachusetts. (U. S. Geological Survey Ninth Annual Report)

Sears, John Henry (1905): The Physical Geography, Geology, Mineralogy and Paleontology of Essex County.

Palache, Charles (1907): Phenacite as an Alteration Product of Danalite from Gloucester, Mass. (American Journal of Science 24:252-255).

Dennen, W. H. (1992): Bedrock geologic map of the Gloucester and Rockport Quadrangles, Essex County, Massachusetts.

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