Abstract

In 1942-44, about 120 Connecticut pegmatites were examined for beryl and other minerals during investigations by the Federal Geological Survey. Most of the pegmatites lie in the Middletown district, occurring principally in the Bolton schist and Monson gneiss. The pegmatites range from distinctly zoned bodies to those that are essentially uniform mixtures of the component minerals. Beryl in the zoned pegmatites commonly is present in greater concentration in one or more zones than in others. It occurs in the majority of pegmatites examined, but on the basis of crystal counts only 10 pegmatites, either in whole or in sizable part, average 0.2% or more beryl. Six structural types of beryl deposits are described and illustrated: border-zone, wall-zone, intermediate-zone, pod, fracture-controlled, and disseminated. Some pegmatites contain two or more types.Grades and tonnages of 14 beryl-bearing pegmatites are tabulated. Total indicated and inferred beryl-bearing pegmatite is 207,885 tons containing 859 + tons of beryl. Most of the beryl is in crystals too small to be economically separable by hand sorting, and barring a marked increase in the price of beryl, milling operations would have to be supported primarily by the yield of salable feldspar, scrap mica, and possibly quartz.

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