Constraints on abundance, composition, and nature of X‐ray amorphous components of soils and rocks at Gale crater, Mars

Abstract

X-ray diffraction patterns of the three samples analyzed by Curiosity's Chemistry and Mineralogy (CheMin) instrument during the first year of the Mars Science Laboratory mission-the Rocknest sand, and the John Klein and Cumberland drill fines, both extracted from the Sheepbed mudstone-show evidence for a significant amorphous component of unclear origin. We developed a mass balance calculation program that determines the range of possible chemical compositions of the crystalline and amorphous components of these samples within the uncertainties of mineral abundances derived from CheMin data. In turn, the chemistry constrains the minimum abundance of amorphous component required to have realistic compositions (all oxides ≥ 0 wt %): 21-22 wt % for Rocknest and 15-20 wt % for Cumberland, in good agreement with estimates derived from the diffraction patterns (~27 and~31 wt %, respectively). Despite obvious differences between the Rocknest sand and the Sheepbed mudstone, the amorphous components of the two sites are chemically very similar, having comparable concentrations of SiO 2 , TiO 2 , Al 2 O 3 , Cr 2 O 3 , FeO T , CaO, Na 2 O, K 2 O, and P 2 O 5 . MgO tends to be lower in Rocknest, although it may also be comparable between the two samples depending on the exact composition of the smectite in Sheepbed. The only unambiguous difference is the SO 3 content, which is always higher in Rocknest. The observed similarity suggests that the two amorphous components share a common origin or formation process. The individual phases possibly present within the amorphous components include: volcanic (or impact) glass, hisingerite (or silica + ferrihydrite), amorphous sulfates (or adsorbed SO 4 2À ), and nanophase ferric oxides.

Recognizing sulfate and phosphate complexes chemisorbed onto nanophase weathering products on Mars using in-situ and remote observationsk

“…Furthermore, SAM m/z 18 data of the Sheepbed mudstone have a shoulder near 275 °C, consistent with allophane (Ming et al 2014). However, calculations of the composition of the crystalline and amorphous components using mineralogy from CheMin and bulk chemistry from APXS show that the amorphous materials in Rocknest and Sheepbed are relatively poor in Al 2 O 3 , so allophane would only be a minor phase if present at all (Dehouck et al 2014;Morris et al 2015a). SAM data from Rocknest and Sheepbed show SO 2 evolutions from ~450-800 °C, where Rocknest data have two peak temperatures at ~500-550 and ~700-750 °C (McAdam et al 2014) and Sheepbed data have peak temperatures at 600-625 °C with a shoulder at ~675 °C (Ming et al 2014).…”

“…Chemical data from APXS in Gusev show that rocks and soils can have up to ~5 wt% P 2 O 5 and ~30 wt% SO 3 (Ming et al 2006), but phase models of the mineralogy of martian rocks and soils assume that none of the phosphate or sulfate is chemisorbed onto weathering products. Calculations of the composition of the X-ray amorphous component of the Rocknest soil at Gale crater show abundances of ~2-3 wt% P 2 O 5 and ~10-17 wt% SO 3 (Blake et al 2013;Dehouck et al 2014;Morris et al 2015a), and the X-ray amorphous component in the Sheepbed mudstone has abundances of 2-3 wt% P 2 O 5 and 0-11 wt% SO 3 (Vaniman et al 2014;Dehouck et al 2014;Morris et al 2015a). Phosphate and sulfate could be chemisorbed onto the surfaces of nanophase minerals in these samples or present as discrete amorphous phases, such as amorphous sulfate salts (Morris et al 2015b).…”

“…X-ray diffraction data measured by the Chemistry and Mineralogy (CheMin) instrument on the Mars Science Laboratory (MSL) Curiosity rover show that amorphous phases are important portions of rocks and soils at Gale crater. Models of CheMin data from the Rocknest sand shadow and the Sheepbed mudstone determined that both samples are composed of ~30 wt% amorphous phases Blake et al 2013;Vaniman et al 2014), and calculations of the composition of the amorphous component suggest these samples may be composed of 40-50 wt% amorphous phases (e.g., Dehouck et al 2014;Morris et al 2015a).…”

Evidence for a widespread basaltic breccia component in the martian low-albedo regions from the reflectance spectrum of Northwest Africa 7034

“…A mixture of these components (as well as minor dust) is a plausible make-up for the low-albedo regions of Mars. The $30% amorphous component identified in rocks and soils at Gale Crater (Vaniman et al, 2014) may be mostly basaltic glass (Dehouck et al, 2014), representing an input from impact materials into the regolith. Certain dark regions in the northern plains may host more of this glass, explaining their enigmatic spectral shapes (Horgan and Bell, 2012).…”

Amorphous salts formed from rapid dehydration of multicomponent chloride and ferric sulfate brines: Implications for Mars

“…Supporting measurements from the APXS and SAM instruments have constrained the bulk chemistry (including S and Cl) and hydrated nature of the amorphous fraction (Leshin et al, 2013;McAdam et al, 2014;Dehouck et al, 2015;Morris et al, 2015a); however, in general, the phase(s) that comprise this fraction are poorly constrained. A variety or combination of phases are plausible, including volcanic glasses, allophane (Morris et al, 2013), hisingerite (Milliken and Bish, 2014), amorphous sulfate (Sklute et al, 2015;Dehouck et al, 2014), chemisorbed sulfate on nanophase materials (McAdam et al, 2014;Rampe et al, 2016), or other nanophases (e.g., Dehouck et al, 2016). Important steps toward constraining the composition(s) of the constituents of the amorphous fraction include determining the possible formation mechanisms of amorphous materials, their stability under Martian conditions (e.g., Dehouck et al, 2016), and their spectral and X-ray diffraction characteristics.…”