PROPERTIES OF MUSCOVITE FROM PEGMATITES IN THE SOUTHEASTERN UNITED STATES
Muscovite-bearing granitic pegmatites occur in the Blue Ridge and Piedmont regions of the southern Appalachian Orogen. Classified as deep-seated intrusions enclosed in medium-to-high grade metamorphic rocks, they typically lack open crystal-line cavities and seldom show either obvious connections to granitoid plutons or batholiths or evidence of rare element enrichment (e.g., B or Li). Mineralogically simple, plagioclase (Pl), quartz (Qtz), K-feldspar (Kfs) and muscovite (Ms) are the dominant phases. Approximately half of these pegmatites show simple zonation (core [Qtz ± Kfs], intermediate zone [Kfs + Qtz], wall zone [Pl + Qtz + Ms], border zone [Qtz + Pl]), with coarse-grained muscovite occurring near the cores of zoned pegmatites or the centers of unzoned pegmatites.
Mica mining in the late 1800s and early 1900s was the first historic utilization of the pegmatites. While feldspar and quartz constitute the focus of recent mining operations, muscovite was deemed a strategic wartime mineral and extensive investigations of muscovite-bearing pegmatites by the U.S. Geological Survey during WWII serve as sources of data for this study. Very coarse-grained muscovite (> 50 cm diameter) has been documented from mines within all pegmatite districts studied from Virginia through Alabama. Much of the muscovite is bent or strained, but crystals or parts thereof capable of producing the artifacts are known from all Southeastern pegmatite districts; size was not a limiting factor in the selection of muscovite mining sites by prehistoric Native Americans.