Rockport, Essex Co., Massachusetts, USA
|Latitude & Longitude (WGS84):||42° 39' 20'' North , 70° 37' 13'' West|
|Latitude & Longitude (decimal):||42.6555555556, -70.6202777778|
The town of Rockport was separated from Gloucester and incorporated in 1840. Granite was quarried here beginning in 1823. Interesting minerals occur in granite quarries and other bedrock exposures of alkaline Cape Ann granite and associated pegmatites and miarolitic cavities.
McKinstry (1921) described some of the town's mineralogical highlights: "More than fifty years ago attention was called to the unusual mineral occurrences at Rockport, on Cape Ann, by J. P. Cooke's description of danalite, a new beryllium mineral, and subsequently of cryophyllite, a new lithium mica. Besides being the type locality for these species, the Rockport quarries have afforded an interesting list of rare-earth minerals, and, perhaps most unusual of all, large tabular crystals of fayalite, normally an utter stranger to granitic rocks."
Mineral ListMineral list contains entries from the region specified including sub-localities
29 valid minerals. 2 (TL) - type locality of valid minerals.
This information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This data will improve over time as more accurate maps and data sets are added.
|Permian - Carboniferous252.17 - 358.9 Ma||Carboniferous-Permian sedimentary rocks|
|Silurian - Ordovician419.2 - 485.4 Ma||Ordovician-Silurian plutonic: undivided granitic rocks|
Plutonic: undivided granitic rocks
|Wenlock - Late Ordovician427.4 - 458.4 Ma||Cape Ann Complex|
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 Macrostrat.org
Garrity, C.P., and Soller, D.R.,. Database of the Geologic Map of North America: adapted from the map by J.C. Reed, Jr. and others (2005). U.S. Geological Survey Data Series 424 .
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.
Localities in this Region
Cooke, Josiah P., Jr. (1867): On Cryophyllite, American Journal of Science and Arts: 48: 217.
Knowlton, W. J. (1867). On a new mineral from Rockport, Massachusetts [Cyrtolite], American Journal of Science and Arts, 2nd Series, 44: 224-226.
Shaler, N. S. (1888): The Geology of Cape Ann, Massachusetts, USGS Ninth Annual Report.
Merrill, George P. (1889): The Collection of Building and Ornamental Stones in the U.S. National Museum, p. 287.
Warren, Charles H. (1903) Anthophyllite [= Ferro-anthophyllite] and Fayalite from Rockport, Massachusetts, American Journal of Science, 4th series: 16: 337.
Sears, John Henry (1905): The Physical Geography, Geology, Mineralogy and Paleontology of Essex County.
McKinstry, H. E. (1921): The Minerals of Rockport, Massachusetts, American Mineralogist: 6: 56-60.
Palache, Charles (1950): Fayalite at Rockport, Massachusetts, American Mineralogist: 35: 877-881.
Dunn, P. (1976): Genthelvite and the helvine group, Mineralogical Magazine: 40: 627-636.
Lyons, Paul (1976): The Chemistry of Riebeckites of Massachusetts, Mineralogical Magazine: 4: 473-479.
Bozhilov, K. N. & B. W. Evans (2001): Ferroanthophyllite in Rockport grunerite: A transmission electron microscopy study, American Mineralogist: 86(10): 1252-1260.