A THIN SECTION STUDY OF MINERAL FLUORESCENCE

Fluorescence is a form of luminescence produced by activator trace elements in minerals exposed to ultraviolet light. The geochemical variables responsible for fluorescence are relatively well understood, but little work has been done to characterize the property in minerals at the microscopic level in thin sections. This project examined the fluorescence of three minerals; calcite (CaCO₃); fluorite (CaF₂) and willemite (Zn₂SiO₄); through a combination of macroscopic and microscopic petrography. The samples all came from Franklin, NJ and were drawn from the Alan Borg Collection, a large suite of largely fluorescent minerals that were donated to the University of South Alabama in 2010. Multiple samples of each of the three target minerals were selected based upon fluorescence intensity during exposure to short wave (10-300 nm) and long wave (300-420 nm) ultraviolet light. A total of 25 thin-sections were made from the specimens and half of these were polished in order to improve surface quality. This study successfully demonstrated that fluorescence can be observed in mineral thin-sections and recorded through photomicroscopy. Photographic quality and detail were better for polished thin-sections suggesting that surface quality (i.e., the level of surface ‘roughness”) is an important consideration in microscopic examination of mineral fluorescence. Surface quality is not relevant for macroscopic examination. The intensity and color of fluorescence is largely controlled by the concentrations of chemical “activators” and/or “quenchers”. Consequently, the next step in this project will be geochemical characterization of the target minerals using electron microprobe analysis.