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USA | |
| Gleba, Peter P. (2008) Massachusetts Mineral and Fossil Localities. Kreueger Enterprises, Inc. |
| Gleba, Peter P. (2008) Massachusetts Mineral and Fossil Localities. Kreueger Enterprises, Inc. |
| Gleba, Peter P. (2008) Massachusetts Mineral and Fossil Localities. Kreueger Enterprises, Inc. |
| P Cristofono collection , 2009 |
| Eckert (1987): Earth Treasures Vol.1: The Northeastern Quadrant. Sears, John Henry (1905): The Physical Geography, Geology, Mineralogy and Paleontology of Essex County, Massachusetts |
| Sears, J. H.(1905): The Physical Geography, Geology, Mineralogy and Paleontology of Essex County. |
| Emerson, Benjamin K. (1895) A mineralogical lexicon of Franklin, Hampshire, and Hampden counties, Massachusetts. Bulletin Vol. 126. US Geological Survey doi:10.3133/b126 |
Blackburn Circle locality, Gloucester, Essex County, Massachusetts, USA