Elishua D. Shepherd


Years participated in RESESS: 2023


An Overview

Program: RESESS Socorro

Major: Earth and Space Exploration (Geological Science)

Academic Affiliation: Arizona State University


Elishua is an incoming senior at Arizona State University majoring in Earth and Space Exploration (Geological Science). He is interested in geomorphology and mineral research within the greater Southwest region of the United States. This summer, Eli will be partnering with his mentors Dr. John Rakovan and Kelsey McNamara to analyze Turquoise mineral samples using X-Ray diffraction. This is to understand the mineralogical differences between the specimens with respect to their chemical compositions and geological locations. His research will be based in New Mexico, although the mineral specimens to be analyzed are from across the globe. In the future, Elishua wants to become a tenured professor at a research university with hopes to inspire younger Indigenous students to pursue a career in geosciences.


Turquoise is a gemstone that has been praised for its beauty in many parts of the world, especially in the American Southwest. Turquoise comes in a spectrum of colors from blue to green with varying shades and intensities. Previous studies regarding turquoise have yet to investigate how color changes depending on turquoise group mineralogy. In this study, 42 alleged turquoise samples of varying color and one alleged chalcosiderite sample were analyzed by powder X-ray diffraction to investigate mineralogical variation in and among the samples. We analyzed 3 to 7 samples each from eight mining districts in New Mexico. Samples were processed to remove as much of the matrix as possible. Data were compared to the ICDD database for mineral phase identification. Special attention was paid to peak placement and intensity of the XRD data from turquoise group minerals (TGM) in the samples. Despite having a range of colors and coming from different mineral deposits, most of our samples shared similar diffraction patterns with only subtle differences in peak position and intensity. Diffraction data were relatively weak with broad peaks due to the fine grained nature and poor crystallinity of TGM. Slight variations in measured peak positions (centroids) suggest the possibility of solid solutions among TGM in our samples. Data quality and the close proximity of peaks among TGM prevent quantification of elemental exchange. One sample was identified as the non- turquoise group mineral prosopite, and the chalcosiderite was identified as planerite. Our results show that color variation did not have a significant influence over diffraction patterns. We also show that positive identification based purely off color can be problematic for minerals with similar color and fine-grained nature. Future work should focus on chemical analyses to determine the elements associated with solid solutions and their correlation with color.