- Names
-
- A. Pisello
- M. Fastelli
- M. Baroni
- A. Musu
- B. Schmitt
- O. Poch
- P. Beck
- M. Petrelli
- M. Porreca
- A. Zucchini
- P. Comodi
- D. Perugini
- Title
- Visible and Near Infrared (VNIR) spectroscopy to decipher glass and crystal content of lab-made Martian volcanic analogues
- Abstract
- Understanding how the glass/crystal ratio influences the spectral response of volcanic rocks is crucial for interpreting planetary remote sensing data. Here, four mafic volcanic rocks were synthesized to simulate a possible Martian composition, with identical bulk chemistry but different mineralogical assemblages, ranging from fully amorphous to ~70 wt.% crystalline, in order to investigate how crystallization affects reflectance spectra in the Visible and Near-Infrared (VNIR) range. Bi-directional VNIR reflectance was collected at room temperature across a range of incidence (0°, 30°, 60°) and emergence (−70° to +70°) angles. The diagnostic absorption features of the two most abundant phases, pyroxene and glass, are not distinguishable in the acquired spectra, and can even reproduce the spectral fingerprint of olivine, which is absent from the samples; only minor iron oxides (magnetite and hematite, ~1–5 wt.%) produce clearly identifiable absorptions. Instead, spectral slope emerges as the primary proxy for crystallinity: NIR/VNIR slope decreases systematically with increasing crystal content, driven jointly by progressive incorporation of iron oxides and loss of the positive-slope contribution from residual glass. Principal Component Analysis coupled with k-means clustering independently confirms this control, identifying three spectral clusters that map onto the glass/crystal ratio of the samples. This decoupling between silicate mineralogy and spectral response indicates that the crystallinity of a mafic terrain cannot be inferred from pyroxene- or glass-related absorptions alone, but rather from spectral slope and iron-oxide features. These results provide an experimental basis for previous hypotheses linking the spectral diversity of Martian mafic terrains to crystallinity and oxidation state, and highlight variable glass abundance as a further, underconsidered contributor to future spectral interpretations of the Martian surface.
- Keywords
- spectroscopy, bidirectional reflection, bidirectional reflectance spectra, BRDF, data analysis, VNIR, visible, near-IR, XRPD, SEM, phase, amorphous, crystalline, band position, band depth, band area, mineral, silicate glass, volcanic glass, clinopyroxene, oxides, augite, Mars
- Content
- sample, spectral data, BRDF data, planetary sciences
- Year
- 2026
- Journal
- Journal of Geophysical Research - Planets
- Document type
- article
- Publication state
- in press