MINERALS OF THE HENRYTON PEGMATITE, CARROLL COUNTY, MARYLAND

Pegmatites, located in Howard, Carroll, and Baltimore Counties, Maryland, were mined for feldspar in the early 1900’s. These pegmatites were identified and mapped in quadrangle, county and state publications into the 1970’s. Detailed descriptions of the pegmatite mineralogy and geochemistry are lacking or very generalized. Since this time, recently published geologic maps have overlooked most of the pegmatites. The Henryton pegmatite is now omitted from the Howard County geologic map, despite its large size of approximately 5 km long and 0.25 km wide, reinforcing the general comment of “no pegmatites in Maryland”.

Current research is providing a general description of this pegmatite including the mineralogy, classification, structure and field relationships to determine if a single or multiple pegmatites are present, and to provide insight to the relationship and history within Appalachian tectonics. X-ray diffraction and energy dispersive spectroscopy have identified the minerals present which include quartz, K-feldspar, plagioclase, muscovite, spessartine, beryl and traces of zircon and apatite. Feldspar and muscovite samples were collected from the most highly fractionated portions of the pegmatite exposures for determining trace element chemistries, pegmatite evolution, classification and possible granitoid sources. Core to rim samples were taken from the largest crystals for zoning studies. Zircons will be used for age dating.