¹Erwin Dehouck,¹Scott M. McLennan,²Pierre-Yves Meslin,³Agnès Cousin
¹Department of Geosciences, State University of New York at Stony Brook, Stony Brook, NY, USA
²Institut de Recherche en Astrophysique et Planétologie, CNRS/Université Paul Sabatier, Toulouse, France
³Los Alamos National Laboratory, Los Alamos, NM, USA

X-ray diffraction patterns of the three samples analyzed by Curiosity’s 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 SiO2, TiO2, Al2O3, Cr2O3, FeOT, CaO, Na2O, K2O and P2O5. 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 SO3 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 SO42−) and nanophase ferric oxides.

Reference
Dehouck E, McLennan SM, Meslin P-Y, Cousin A (2014) Constraints on abundance, composition and nature of X-ray amorphous components of soils and rocks at Gale crater, Mars. Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2014JE004716]

Published by arrangement with John Wiley&Sons