Research Training Program

Amanda Albright
Juniata College
Huntingdon, PA

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

"My experience in the RTP allowed me to explore my geologic interests in an environment that stimulated both my intellect and my curiousity"

Pegmatites are rocks that are chemically and minerallogically similar to granites that form in veins at a late-stage in the granite-forming process. Because of the character of the melt and the method of emplacement, pegmatites form extremely large crystals over a short period of time. Pegmatites are generally enriched in rare elements that form uncommon minerals. For this reason, they are often mined for both industrial and gem-quality minerals The pegmatites of southern California are one of the few regions of pegmatites in the United States that are mined for their high-quality gemstones. The Rincon pegmatite district of northern San Diego County, is part of this region. These pegmatites formed between 90 and 100 million years ago. Mineralogically, these pegmatites are simple, containing primarilly the mineralsquartz, microcline, albite, muscovite, biotite, garnet, schorl and localitzed epidote that is found within fractures. Epidote is a pistachio green to dark green mineral that is rarely found in pegmatites. The purpose of our study is to describe the occurance of epidote within the pegmatites as well as to explain why it is there. We sampled the rocks and performed chemical analyses in order to understand the chemistry of the rocks. The analysis showed that the epidote is enriched in elements such as manganese, titanium, and phosphorus, indicating that it probably formed during the final stage of pegmatite crystallization from a residual fluid. This argument is further proven by the observation that much of the epidote is found in fractures that seem to be completely surrounded by the pegmatite, indicating that they must have been derived internally.