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Great Ring Farm, Newtown, Fairfield Co., Connecticut, USA

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Latitude & Longitude (WGS84): 41° 23' 23'' North , 73° 13' 19'' West
Latitude & Longitude (decimal): 41.38972,-73.22194
GeoHash:G#: dr7gmyc2t
Locality type:Farm
Köppen climate type:Cfa : Humid subtropical climate

A tourmaline locality hosted by the Ordovician Taine Mountain Formation granofels and schist. The matrix generally contains much talc and chlorite. The matrix and the tourmaline crystals are very similar to the more recent and much more productive and well-known tourmaline ledge in Bethel (hosted by the same formation) near the Biermann Quarries

The Great Ring Farm locality is an old so-called "Dana locality" and specimens are in the Yale-Peabody Museum collection, though they are attributed only to "Newtown". Early reference to these crystals (incorrectly) occurring in Monroe "near Lane's Mine" (Dana, 1875) were very general and the precise locality could not be found for decades. The locality is near the intersection of Great Ring Road and Route 34 in Newtown not far from the Newtown-Monroe town line and confusingly there is also a Great Ring Road nearby in Monroe. Earle C. Sullivan, noted local mineral collector, teacher and historian, describes its "rediscovery" on a label that accompanied specimens formerly in his collection:

"This location was rediscovered by some of my students in Bpt. [Bridgeport, Connecticut] High School circa 1938; (Ray Malone, Wm. Schneider and Ed Burke) It is on private residential property, off Route 34. Some of the crystals are quite large. With Mr. S. C. Moore, Bpt. Hi. Principal, we saw one at least 2 1/2 in. x 1 1/2". It was shown us by Sherriff [sic] Olmstead who lived on Rte 111 near the Monroe-Trumbull town line."

Their identification as being the species dravite is apparently based on the dark brown color and has not been confirmed by analyses. Earle Sullivan specimen labels have schorl crossed out and dravite written in below! A similar problem with species identification exists with the Bethel tourmalines.

Select Mineral List Type

Standard Detailed Strunz Dana Chemical Elements

Mineral List

Detailed Mineral List:

Formula: A(D3)G6(T6O18)(BO3)3X3Z
Habit: short prismatic, doubly-terminated by rhombohedrons
Colour: dark brown to black, black
Description: Described in Dana and Brush (1875) as "perfect dark brown crystals in mica-slate...sometimes to two inches in length and breadth." These dark brown to black crystals are sometimes referred to in old literature as dravite, though that identification is unconfirmed.
Reference: Harold Moritz collection; Labels from Earl Sullivan collection; Dana and Brush (1875): A System of Mineralogy. Fifth edition. p.369

List of minerals arranged by Strunz 10th Edition classification

Unclassified Minerals, Rocks, etc.

List of minerals arranged by Dana 8th Edition classification

Unclassified Minerals, Rocks, etc.

List of minerals for each chemical element

B TourmalineA(D3)G6(T6O18)(BO3)3X3Z
O TourmalineA(D3)G6(T6O18)(BO3)3X3Z

Regional Geology

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

Ordovician - Neoproterozoic
443.8 - 1000 Ma

ID: 3190671
Precambrian-Phanerozoic sedimentary rocks

Age: Neoproterozoic to Ordovician (443.8 - 1000 Ma)

Lithology: Mudstone-carbonate-sandstone-conglomerate

Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529. [154]

Middle Ordovician
458.4 - 470 Ma

ID: 2772242
Brookfield Gneiss

Age: Middle Ordovician (458.4 - 470 Ma)

Stratigraphic Name: Brookfield Gneiss

Description: Brookfield (dioritic and granodioritic) Gneiss (including Newtown Gneiss of Crowley, 1968) - Dark and light, commonly speckled or banded, medium- to coarse-grained, massive to poorly foliated gneiss, composed of plagioclase, biotite, and hornblende, generally with quartz and K-feldspar, the latter commonly as megacrysts 1 to 3 cm across (also plagioclase megacrysts in darker rocks), locally associated with amphibolite or hornblende schist.

Comments: Part of Central Lowlands; Iapetus (Oceanic) Terrane - Connecticut Valley Synclinorium; Newtown Gneiss of Crowley, 1968 (CT008).

Lithology: Major:{orthogneiss}, Incidental:{amphibolite, amphibole schist}

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. [133]

Data and map coding provided by, used under Creative Commons Attribution 4.0 License


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Dana, James D. (1875): A System of Mineralogy. Fifth edition. Wiley & sons, New York: 369.
Specimen labels from the former Earl C. Sullivan collection.

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