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Diamond Hill (Ashaway Village), Ashaway, Hopkinton, Washington Co., Rhode Island, USA

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Latitude & Longitude (WGS84): 41° 25' 24'' North , 71° 47' 10'' West
Latitude & Longitude (decimal): 41.4233333333, -71.7861111111

Quartz crystals were known here long before the large amethyst discovery.

Mineral List

Regional Geology

Neoproterozoic541 - 1000 MaPlainfield Formation

Major:: {quartzite},Minor:: {mica schist}

Plainfield Formation - Pale-tan to gray, fine-grained quartzite, and pale- to medium-gray quartz-mica schist. Quartzite is massive to layered (bedded?). Includes Plainfield Formation and some rock mapped formerly as Blackstone Series.

Part of Hope Valley Subterrane

Neoproterozoic541 - 1000 MaNeoproterozoic plutonic: undivided granitic rocks

Plutonic: undivided granitic rocks

Neoproterozoic541 - 1000 MaNeoproterozoic intrusive and metamorphic terranes

Intrusive and metamorphic terranes

Mixtures of metamorphic and intrusive or plutonic rocks, tracts known as crystalline, migmatitic terranes, moderately to highly metamorphosed rocks of unknown origin with or without intrusions. This classification is inherently prone to variable interpretation, as other compilers might distinguish some packages by their metamorphic or gneissic protoliths, and the associated age ranges may be more variable.

References for regional geology:

Data provided by

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.

3 valid minerals.

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.


- Rocks & Minerals (1986): 61: 247-250
- Rakovan, J., Mitcheltree, D.B., Benton, L., and Avella, S. (1995) Amethyst on milky quartz from Hopkinton, Rhode Island. Mineralogical Record 26:83-89.

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