Great Hill Pond Brook pegmatite, Cobalt, East Hampton (Chatham), Middlesex Co., Connecticut, USA
|Latitude & Longitude (WGS84):||41° 34' 15'' North , 72° 33' 34'' West|
|Latitude & Longitude (decimal):||41.57083,-72.55944|
A granite pegmatite exposed at the waterfall on Great Hill Pond Brook about 350 meters downstream of the pond. Prospected before 1927 based on its first mention in the literature by Rice and Foye (1927):
Schooner (1958 and/or 1961) mentions well-formed black tourmaline and "spessartine" (likely almnadine-spessartine mix) from here. In 1961 he describes similar garnet from the Nathan Hall quarry on Clark Hill a mile or so to the NE www.mindat.org/loc-29586.html. Schooner later incorrectly calls the Nathan Hall Quarry the "Hale Quarry" in his unpublished central Connecticut mineralogy. This occurs in the text for "spessartine" localities right after he mentions garnet from the Great Hill Pond Brook falls pegmatite. This may have led to confusion by Hiller (1971) who marks this prospect on a map of the Cobalt area localities as "Nathan Hale [sic] Quarry". While it may just be an error by Hiller (the source he used for the name is not recorded), it is possible that Nathan Hall, who's family owned much land in the area in the 19th century, prospected this pegmatite as well, given that Foye in 1922 stated that the Nathan Hall Quarry was long abandoned. Nathan Hall had quarry properties in Haddam Neck also. However, so far the exact history of this little prospect is unknown.
The brook is the border between Portland (west) and the Cobalt section of East Hampton (east), but because the pegmatite extends mostly east of the brook, it is listed here as in the latter town. The site is now residential private property.
5 valid minerals.
Rock Types Recorded
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Entries shown in red are rocks recorded for this region.
This geological map and associated 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 does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.
Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org
|Late Ordovician - Middle Ordovician|
443.8 - 470 Ma
|Collins Hill Formation|
Age: Ordovician (443.8 - 470 Ma)
Stratigraphic Name: Collins Hill Formation
Description: ( = Partridge Formation of New Hampshire) - Gray, rusty-weathering, medium- to coarse-grained, poorly layered schist, composed of quartz, oligoclase, muscovite, biotite, and garnet, and commonly staurolite, kyanite, or sillimanite, generally graphitic, interlayered with fine-grained two-mica gneiss, especially to the west, and with calc-silicate and amphibolite layers, also rare quartz-spessartine (coticule) layers.
Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052. 
Schooner, Richard. (1958), The Mineralogy of the Portland-East Hampton-Middletown-Haddam Area in Connecticut (With a few notes on Glastonbury and Marlborough). Published by Richard Schooner; Ralph Lieser of Pappy’s Beryl Shop, East Hampton; and Howard Pate of Fluorescent House, Branford, Connecticut.
Stugard, Frederick, Jr. (1958), Pegmatites of the Middletown Area, Connecticut. USGS Bulletin 1042-Q.
Jones, Robert W. (1960), Luminescent Minerals of Connecticut, a Guide to Their Properties and Locations.
Schooner, Richard. (1961), The Mineralogy of Connecticut. Fluorescent House, Branford, Connecticut.
Hiller, John, Jr. (1971), Connecticut Mines and Minerals. Privately published: 52.
Schooner, Richard. (circa 1980s), Untitled manuscript on central Connecticut mineralogy.