8 Advancing Mineral Science and Exploring Planetary Surfaces: In Honor of MSA Dana Medalist, Elizabeth B. Rampe, Part I

This session honors MSA Dana Medalist Elizabeth B. Rampe, celebrating her contributions to Martian mineralogy and planetary science. We invite studies on in-situ and orbital planetary observations, lab/field data integration, and analog materials for extraterrestrial exploration.Sarah Simpson

Sunday, 19 October 2025
8:00 AM - 12:00 PM
HBGCC, 214C

X-ray amorphous materials in phyllosilicate- and sulfate-bearing units in Gale crater, Mars

Paper number: 8-2
Program: Technical Sessions
Time: 8:30 AM – 8:45 AM

Authors

Abstract

X-ray amorphous materials comprise ~20-70 wt% of every rock and soil sample analyzed by the CheMin X-ray diffractometer (XRD) on board the Curiosity rover in Gale crater. Here we use the term ‘X-ray amorphous materials’ to describe nanocrystalline phases that scatter X-rays (i.e., they may contain short-range atomic order). The origin(s) of these phases remains speculative; in Gale crater this material is likely a complex mixture of primary aluminosilicate glass(es), sulfate(s) and other secondary alteration or diagenetic products. As Curiosity traversed across the smectite-rich region, transitional units and upwards into the sulfate unit, several noteworthy sedimentological and mineralogical trends were observed that indicate a period of gradual drying including the loss of phyllosilicates, from older clay-rich sandstones and mudstones to the younger, phyllosilicate-barren, hydrated Mg-sulfate-rich (+/- Fe(II) carbonate) sandstones. Here we present major trends observed in the abundances and compositions of the amorphous component across these regions of major change, as determined using FULLPAT modeling combined with a mass balance calculation, and derive their context in combination with the mineralogy.

The proportion of amorphous material in each sample has gradually increased across the traverse (smectite-rich strata ~36 wt%; transitional units ~50 wt%; and sulfate unit ~58 wt%). This increase in amorphous abundance coincides with the loss of smectites and correlates with the inferred exhaustion of surface water. This may have been punctuated by brief wet-dry cycling, precluding the crystallization of widespread, abundant phyllosilicates while allowing the amorphous material to persist without forming long-range order. The amorphous material is primarily composed of SiO2, FeOT, MgO and SO3, with varying amounts of other minor phases. There is a consistent anticorrelation between SiO2 and SO3 which suggests there are at least two amorphous endmembers: one that is silicate (+/- FeOT) and one that is more sulfate (+/- MgO) -rich, reflective of mixture(s) of primary and secondary materials (e.g., basaltic glasses, sulfates with a similar composition to the crystalline phases detected by CheMin). The silicate endmember could also contain X-ray amorphous clay minerals, representative of destroyed clay mineral components, or nontronite-like precursors that did not crystallize further due to the lack of sufficient water in the upper strata. Curiosity will continue to explore these relationships to help elucidate the alteration history across this region in Gale crater.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412044

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