MOONSTONE AND OTHER GEM FELDSPARS OF THE BRIMFIELD SCHIST AND NEIGHBORING GNEISS AND GRANULITE

Gem-quality moonstone is readily available within glacial till and the schists, gneisses, and granulites in eastern Hampden County, Massachusetts. Mapping these deposits has been made easy with the use of the Esri 'Collector' application. Older methods involved additional hardware, which is relatively cumbersome for geographers in the face of modern technology. The gem moonstone is named for its characteristic schiller effect; the billowing of light across a polished surface resembles the light reflected by the moon. Large angular cleavage fragments and sub-rounded alluvial fragments are easily found in gravel patches throughout Holland, Wales, and Brimfield, among others. The gems are available in a wide array of colors and compositions (Emerson, 1917 and Zen et al., 1983). Their presence in Brimfield has been known at least as far back as the late 1800s (Emerson, 1895). Since then, scientists have learned a great deal about what gives a moonstone its characteristic schiller and how it is distinguished from labradorite, sunstone, gem orthoclase, and the other feldspar gemstones.