X-ray Diffraction Results from Mars Science Laboratory: Mineralogy of Rocknest at Gale Crater

Abstract

The Mars Science Laboratory rover Curiosity scooped samples of soil from the Rocknest aeolian bedform in Gale crater. Analysis of the soil with the Chemistry and Mineralogy (CheMin) x-ray diffraction (XRD) instrument revealed plagioclase (~An57), forsteritic olivine (~Fo62), augite, and pigeonite, with minor K-feldspar, magnetite, quartz, anhydrite, hematite, and ilmenite. The minor phases are present at, or near, detection limits. The soil also contains 27 ± 14 weight percent x-ray amorphous material, likely containing multiple Fe(3+)- and volatile-bearing phases, including possibly a substance resembling hisingerite. The crystalline component is similar to the normative mineralogy of certain basaltic rocks from Gusev crater on Mars and of martian basaltic meteorites. The amorphous component is similar to that found on Earth in places such as soils on the Mauna Kea volcano, Hawaii.

Determining volcanic eruption styles on Earth and Mars from crystallinity measurements

“…A calculation of the amorphous component chemical composition from a combination of CheMin and alpha particle X-ray spectrometer analysis on the Rocknest sand shadow sediment indicates a low-SiO 2 (37.2 wt%) component 33 . This is consistent with deconvolution of XRD patterns that indicate a best-fit to the CheMin XRD data with a 'Gusev-composition basaltic glass 38 .' Although multiple lines of evidence suggest the presence of a basaltic glass component, the origin and nature of this amorphous component is unknown 39 .…”

“…4) 33 , indicating a potential source distinctive from that of the sediments comprising the mudstone rocks. With 38,39 . Bragg peaks in the diffraction pattern represent the crystalline component while the broad hump between B10 and 40°2y is characteristic of the amorphous component.…”

“…4) (compared with independent estimates from XRD 38 and mass balance 33 approaches, yielding 73±14% and 55% crystallinity, respectively). A calculation of the amorphous component chemical composition from a combination of CheMin and alpha particle X-ray spectrometer analysis on the Rocknest sand shadow sediment indicates a low-SiO 2 (37.2 wt%) component 33 .…”

“…A number of lava flows were also analysed to (1) provide a relative check of cooling rates and (2) 39 were processed using our calibrated technique to determine the proportion of amorphous material. In contrast to the Siemens D500 that operates in reflection geometry mode with a CuKa X-ray source, the CheMin instrument operates in transmission geometry with a CoKa X-ray source 38 . While the absolute positions of peaks will vary as a result of the differences between wavelengths of CuKa and CoKa X-rays, overall differences in intensity will be relatively minor.…”

“…Although alteration of amorphous glass may result in the formation of crystalline materials (for example, zeolites), a byproduct of both hydrothermal alteration and chemical weathering of glass on Mars is the formation of npOx. NpOx is an amorphous Fe-bearing constituent that may include haematite, goethite, ferrihydrite, hisingerite, schwertmanite, akaganeite and the Fe 3 þ -rich particles that pigment iddingsite and palagonite, and is presently not distinguished from glass based on remote XRD analysis [33][34][35][36][37][38][39] . Alteration of glass is considered to be one of the primary means of npOx formation in Martian volcanic deposits [33][34][35][36][37] .…”