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Mt. Tom prospects, Moodus, East Haddam, Middlesex Co., Connecticut, USA
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Beryl
Mt. Tom prospects, Moodus, East Haddam, Middlesex Co., Connecticut, USA

Photo: Rowan Lytle
Latitude: 41°29'35"N
Longitude: 72°28'31"W
 
 
The Mount Tom prospect is in East Haddam on the point of land forming the confluence between the Salmon and Moodus Rivers. Beryls have been known from here since at least circa 1900 (Davis, 1901). According to Barton and Goldsmith (1968), it was on a tract of approximately 32 hectares owned circa 1968 by Marja Rozwadowska and under lease in 1962 to Joseph Koslowski of Cromwell. It has been prospected in four small pits opened for gem golden beryl in 1960-61. It is now part of Machemoodus State Park.

Near the top of the mountain are two small concordant pegmatite sills. The larger of the two sills bifurcates northward along strike. The sills are exposed for about 190 m along strike, pinching out to the north, and disappear beneath overburden but probably pinch out (based on lack of topographic expression) to the south. The sills dip to the west variably, but generally about 25°-45° W. The smaller sill to the west is about 1.3 m thick on the average and the larger sill about 2.7 to 3.2 m thick at its maximum, thinning to the south and thinning and bifurcating northward.

The pegmatites, as exposed, are rather poorly zoned but some differentiation can be generalized from inspecting the walls of prospect pits. The outer (wall) zone consists of 1 to 3 m of gray quartz and cream microcline perthite with abundant accessory black tourmaline crystals 2.5 to 12.5 cm in diameter and as much as 0.7 m long. Golden and green beryl crystals average about 2 cm thick by 5 cm long with a maximum size of 15 by 40 cm.

They form about 1 percent of the zone with locally beryl forming as much as 50 percent of a 0.3- by 0.7-meter exposed rock surface. The inner zone is mostly white microcline perthite and gray quartz with about 0.1 percent beryl and only scattered local nests of black tourmaline.

Five very small prospect pits have penetrated the pegmatite from which about 680 kg of hand¬cobbed beryl have been recovered. Any that was gem or specimen quality was disposed of as such for a premium price and rough beryl was mixed with that from other leases held by Koslowski and sold to the U.S. Government purchase depot at Franklin, N.H. Since the cessation of government purchases in 1962 the only activity at the mine was when a mineral club payed to have a blast set off to improve collecting. This activity ceased around the 1970s.

Collecting is not allowed on state of Connecticut property without a permit.

Mineral List

Albite
Beryl
'Columbite'
Microcline
'Monazite'
Muscovite
Quartz
var: Smoky Quartz

Schorl


8 entries listed. 5 valid minerals.

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References

Davis, James W. (1901): The Minerals of Haddam, Conn. Mineral Collector, v. 8, no. 4, pp. 50-54, and no. 5, pp. 65-70.

Schooner, Richard. (1961): The Mineralogy of Connecticut. Fluorescent House, Branford, Connecticut.

Barton, William R. and Carl E. Goldsmith. (1968): New England Beryllium Investigations. U. S. Bureau of Mines, Report of Investigations 7070.

Weber, Marcelle H. and Earle C. Sullivan. (1995): Connecticut Mineral Locality Index. Rocks & Minerals (Connecticut Issue): 70(6)(Nov.-Dec.): 396-409.

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