The following picture, taken by the Curiosity rover in the Gale Crater on Mars in 2016 shows what appears to be a cracked Martian surface, with the Egg Rock nickel-iron meteorite. Ignoring the meteorite, the cracks appear to be infilled with a white substance. Has the white crack infill material ever been identified and if so, what is it?

enter image description here

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    $\begingroup$ When Mars cracked, they only had #17 patching compound on hand, rather than the color-matched #3, so they repaired it with what they had. $\endgroup$
    – Mark
    Commented May 1, 2021 at 17:47
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    $\begingroup$ :-) And most people would probably say oh, a meteorite ! How interesting ! While the story of the rock underneath is telling so much more than a ubiquitious meteorite ... $\endgroup$
    – user40414
    Commented May 1, 2021 at 18:13

1 Answer 1


These can be interpreted as desiccation cracks, filled with calcium- and/or magnesium sulfate (Ca-/Mg-SO4, seen as white material).

Methods used, for brevity citing from the below pop science link:

"... The team took a close physical and chemical look at those polygons using Curiosity's Mastcam, Mars Hand Lens Imager, ChemCam Laser Induced Breakdown Spectrometer (LIBS), and Alpha-Particle X-Ray Spectrometer (APXS) ..."

I believe this setting has led to the hypothesis of a once dried out lake on Mars.



  • $\begingroup$ Overall good, but why would white be specifically calcium sulfate? Magnesium sulfate would be white also. $\endgroup$ Commented May 1, 2021 at 9:23
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    $\begingroup$ Corrected, thanks, that was ambiguous. $\endgroup$
    – user40414
    Commented May 1, 2021 at 9:41
  • $\begingroup$ Added back the color reference in a way that includes both salts. $\endgroup$ Commented May 1, 2021 at 17:50
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    $\begingroup$ @OscarLanzi: Ok. I had it initially in because they wrote it explicitly in the paper. I just forgot the phrase "the white filling <in the cracks of the image> being CaSO4". This was because both substances where mentioned, but the one in the the rock of the paper was identified as CaSO4, not MgSO4. When you said "could be both" it dawned on me that the rock in OP's image is probably not the one from paper ("Old Soaker" or so), so i took it out. In the end, chemically it doesn't matter that much if it is Ca or Mg in the rock in the image with the egg rock on it :-) $\endgroup$
    – user40414
    Commented May 1, 2021 at 18:08

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