Key Points
- Pooja Sheevam and Wendy M. Calvin used LWIR spectroscopy, SEM-EDS, and XRF geochemistry to study the PTA-2 drill core from Hawaii.
- The study emphasized the value of LWIR spectroscopy (5–15 µm) in identifying silicate minerals like pyroxenes, olivines, and feldspars—minerals that are difficult to detect using shortwave infrared techniques.
- The team faced obstacles such as limited spectral libraries and complex mineral mixtures, and used a linear unmixing model to cautiously estimate mineral abundances.
A recent study in the Journal of Volcanology and Geothermal Research led by Pooja Sheevam and Wendy M. Calvin investigated the subsurface of Hawaii. In an effort to learn more about the mineralogical and geochemical transformations that have taken place on Hawaii, the two used longwave infrared (LWIR) spectroscopy, scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and X-ray fluorescence (XRF) geochemistry to investigate the Hawaiian subsurface. By analyzing the PTA-2 drill core on the Big Island on Hawaii, Sheevam and Calvin revealed new insights into mineralogical and geochemical transformations.
To learn more about their study and what scientists should take from it, Spectroscopy sat down with Sheevam to ask her important questions about the study’s methodology and the role spectroscopy played in it. Sheevam conducted this work while a PhD student at the University of Nevada, Reno. She now works as an associate researcher at the New Mexico Bureau of Geology and Mineral Resources.
In Part II, Sheevam discussed LWIR and SWIR more in depth, talking about the advantages that each technique brought to the study (3). In Part III, our discussion with Sheevam focused on the use of long-wave IR (LWIR) spectroscopy in analyzing basaltic rocks, particularly between 5–15 µm. Sheevam highlights in our conversation how her team used LWIR to identify primary silicate minerals like pyroxenes, olivines, and feldspars, which are challenging with shortwave techniques.
Sheevam’s study employed a linear unmixing model to estimate mineral abundances, though results were interpreted cautiously because of limitations in quantification. The challenges the research team faced included the lack of spectral libraries for fine-grain clays and zeolites, and complex mixtures in some cores. High-resolution scans at 50 µm by 50 µm revealed mineral mixtures and spectral variations influenced by crystal orientation and elemental zoning, suggesting a need for further research on spectral changes based on mineral orientation.
This video clip is the third part of a five-part interview with Sheevam. You can view the previous clips in this interview series below.
Part 1
Part 2
References
- Sheevam, P.; Calvin, W. M. Comprehensive Characterization and Geochemical Alteration Pathways of Drill Core From the Humu'ula Groundwater Research Project, Hawaii, USA: I. Pohakuloa Training Area. J. Vol. Geo. Res. 2025, 462, 108311. DOI: 10.1016/j.jvolgeores.2025.108311
- Wetzel, W. Using Spectroscopy to Understand Hawaii’s Hidden Geology. Spectroscopy. Available at: https://www.spectroscopyonline.com/view/using-spectroscopy-to-understand-hawaii-s-hidden-geology (accessed 2025-05-27).
- Wetzel, W. Defining LWIR and SWIR: An Interview with Pooja Sheevam. Spectroscopy. Available at: https://www.spectroscopyonline.com/view/defining-lwir-and-swir-an-interview-with-pooja-sheevam (accessed 2025-06-02).
