Research Training Program

Amie Garcia
South Dakota School of Mines and Technology
Rapid City, South Dakota

Mike Wise, Ph.D.
Supervising Scientist
Department of Mineral Sciences

"This experience has been the
greatest of my life. I got to do
wonderful research on pegmatites,
see things I never would have
seen, and make great new friends
in my field and outside of it."

A Cathodoluminescence Study of Microcline from the Morefield Pegmatite, Virginia

A pegmatite is a rock with exceptionally large crystals that forms from magma that has crept into fractures deep within the Earth’s crust. Pegmatites are important because they can contain rare elements that are not found in large quantities in many places of the world. Pegmatites are an essential source of industrial (feldspar, muscovite) and gem minerals (topaz, aquamarine). These materials are important in our everyday lives; therefore it is crucial that we study pegmatites in order to understand how they form. This research focused on the Morefield pegmatite, which is located in central Virginia. Microcline is the dominant mineral within the pegmatite and is tan to green in color. The focus of the research was to find out how the green microcline (amazonite) formed. Cathodoluminescence (CL) is a process that fires a beam of electrons onto the surface of a mineral sample. The energy from the electron beam excites certain elements within the mineral causing it to glow different colors. Under CL, the tan-colored microcline appears blue whereas the amazonite appears blue-green. The CL study indicates that the tan-colored microcline formed first, and was changed to amazonite as the pegmatite solidified. This change in color was due to the interaction of Pb (lead) present in the microcline structure and fluids that entered fractures in the mineral.

This research was supported by a grant from the National Science Foundation Research Experiences for Undergraduates program, Award Number DBI-0243512.

Letter of gratitude