MARS' "DOUBLET MATERIAL" OBSERVED IN JURASSIC AZTEC SANDSTONE NEAR VALLEY OF FIRE STATE PARK, NEVADA, USA

An enigmatic spectral feature known as "doublet material" has been observed at Mawrth Vallis¹ and Ius Chasma² on Mars. Several different mineralogies have been tested as an origin for this feature, including combinations of jarosite/gypsum, jarosite/smectite, and acid alteration of smectite, but none have provided a perfect fit. New research on a rare Fe/Al Alunite Group solid solution mineral found in the Aztec Sandstone at Buffington Pockets, Nevada, has produced a doublet feature similar to the "doublet material" on Mars when analyzed using VNIR reflectance spectroscopy. XRD analysis revealed a crystalline mineral with an intermediate composition between jarosite and alunite, and spectra produced by this mineral are a match to minima produced by a synthesized jarosite-alunite solid solution. The spectra produced by this intermediate jarosite-alunite solid solution fall within the range of doublet minima from martian examples, with one exact spectral alignment. It is therefore suggested by this study that the reflectance spectra observed in the "doublet material" at Mawrth Vallis and Ius Chasma may be produced by a solid solution of an Fe/Al Group mineral.

1. Bishop, Janice L. et al., 2020, Icarus, v. 341, p.1-12; 2. Wilk, Kierra A., et al. 2023, Icarus, v. 408, p. 1-143