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Merrimack Co., New Hampshire, USA

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Location is approximate, based on center of defined region.
Latitude & Longitude (WGS84): 43° 17' 50'' North , 71° 40' 48'' West
Latitude & Longitude (decimal): 43.29750,-71.68028

Merrimack County was established in 1823.

Note: The geographic coordinates presented are taken from the Webster topo map. The USGS GNIS database presents 29 sets of coordinates for this county.

Mineral List

Mineral list contains entries from the region specified including sub-localities

52 valid minerals.

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

Early Devonian
393.3 - 419.2 Ma
Spaulding Tonalite

Age: Early Devonian (393.3 - 419.2 Ma)

Stratigraphic Name: Spaulding Tonalite

Description: (Spaulding Quartz Diorite of Fowler-Billings, 1949) - Weakly foliated to nonfoliated, spotted biotite quartz diorite, tonalite, granodiorite, and granite; garnet and muscovite may or may not be present.

Comments: Part of the New Hampshire Plutonic Suite (Late to Early Devonian) - Includes synkinematic and postkinematic granitoids related to the Acadian orogeny. Ages range from 410 to 365 Ma. New Hampshire Plutonic Suite: Kearsarge pluton = 393+/-5 Rb/Sr per NH028. Blackwater pluton = 398+/-? U/Pb, monazite per NH030. Pratt Pond pluton = 280+/-6 U/Pb, zircon, 272+/-2 U/Pb, monazite (J.N. Aleinikoff, oral commun., Dec. 1994). 365+/-? U/Pb, zircon, 365+/-? U/Pb, monazite (J.N. Aleinikoff, oral commun., May 1995). Quartz syenite dike (point within formation) = 159 K/Ar per NH037.

Lithology: Major:{quartz diorite,tonalite,granodiorite}, Minor:{granite}

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

Localities in this Region

This page 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.
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