Long Hill (Turkey Hill) prospects, Haddam, Middlesex Co., Connecticut, USA

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Often erroneously referred to as Turkey Hill, which is further south, Long Hill hosts many very small beryl prospects in narrow, zoned pegmatites. Hall (1838) describes specimens obtained from the gneiss quarries on Long Hill, though the emerald color is a bit of an exaggeration:

"I have just procured two of the finest crystals I ever had in my possession. One of them is a perfect hexagonal prism, about two inches long, and an inch and a half in diameter. The faces forming its terminations are at right angles with the sides, and wear as fine a polish as the hand of Nature can produce. The color is a brilliant emerald green, and, indeed, the crystal appears to possess more of the characters of the emerald, than of the beryl."

The prospects are scattered widely, so the reference coordinates given below are for the summit. The following description from Barton and Goldsmith (1968) is the best and most comprehensive:

"The Long Hill prospects are located in Haddam about 12 miles S 20° E from the center of town (fig. 31). They are on 160 acres owned by Mrs. Sona Keirstead which includes the crest of Long Hill. Numerous small prospect pits have been dug by mineral collectors but no organized beryl mining has been attempted. There are several small quarries on the hill which were worked for gneiss dimension stone many years ago.

Beryl occurs in numerous small pegmatite dikes cutting both the hornblende-biotite gneisses and the small concordant quartz veins associated with the gneisses on Long Hill. The gneiss banding and the quartz veins strike N 17° W and dip 75° E. The cross-cutting pegmatite dikes strike an average N 40° E, and dip 65°-75° SE. The exposed dikes (as seen in some of the old stone quarries) are small, up to 8 feet wide by 40 feet long, and are emplaced in a typical en echelon pattern. Gem beryl (green to blue) appears to be an ubiquitous dike constituent. In some of the better exposures beryl appears to comprise 1 percent of the pegmatite mass. Most of the pegmatites, however, are poorly exposed, showing only in small rubble filled pits where prospectors set off a single dynamite charge. The pits are numerous and widely scattered and, coupled with abundant quartz-perthite pegmatite float on the ridge line of Long Hill, indicate that one or several other pegmatites may be concealed beneath overburden. However, no exploration was attempted to evolve an answer to this question.

Exposed pegmatites are fairly well zoned but zoning is not entirely consistent from one pegmatite to the next."

London (1989) notes that most of these unfoliated pegmatites strike discordantly east-west, display sharp contacts, and are muscovite and tourmaline rich with a composition mostly of microcline and quartz, with quartz rich cores. Some have accessory beryl and garnet. This is in contrast to what he maps as "syenitic feldspar pegmatite" which are concordant, weakly foliated, unzoned and contain more abundant albite but lack accessory minerals other than micas and garnet.

Mineral List

Albite Bertrandite Beryl var: Aquamarine

Bismuthinite 'Garnet' Microcline Microlite Group

Muscovite Quartz var: Smoky Quartz Schorl

Topaz

13 entries listed. 10 valid minerals.

References