Buchtel College of Arts and Sciences
Date of Last Revision
Number of Credits
Bachelor of Arts
Date of Expected Graduation
San Diego pegmatites of the Pala and Mesa Grande mining districts are world renowned for their gem-quality minerals and their Li-bearing mineral phases. Pegmatite genesis, especially in San Diego mines, has been a debated topic since the 1900’s (Morgan and London, 2012). Pegmatite genesis is caused by partial melting processes and fractional crystallization that form granitic melts with high concentrations of rare earth elements (REE), such as lithium. Assessing the exact mineralogy and determining the overall textures can provide insight into the crystallization history of pegmatites. In the San Diego pegmatites, lithium-bearing phases, such as lepidolite and pink elbaite (a Na- and Li-rich variety of tourmaline) tend to be early crystallizing phases. Garnet and black schorl tourmaline (Na- and Fe-rich) also appear to crystallize early. Albite (Na-rich feldspar) and muscovite tend to be next in the crystallization sequence, and quartz is the final crystallizing phase and infills any remaining space between the other phases. This crystallization sequence is indicative of a starting melt that is rich in REE, which are removed by crystallization of lepidolite and elbaite, leaving an alkali-rich melt that becomes Si-saturated during the final stages of crystallization. The abundance of Li-bearing minerals in the San Diego pegmatites is important for mining for gemological and lithium resources, which is a pressing societal need given technological reliance on lithium batteries.
Honors Faculty Advisor
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Potter, Gabrielle, "Textural and mineral analysis of pegmatites from the Pala and Mesa Grande Districts in San Diego, California" (2023). Williams Honors College, Honors Research Projects. 1776.