[cpdiii]

Judging by appearances (always dangerous), they are likely to be some type of carbonate (like calcite) or evaporite (like salt).

Looks like mud cracks that one would find in a playa(shallow lake that floods and dries) that has dried out. Cracks could have been filled in with wind blown sediments, buried and then have mineral replacement. You can find the same thing here on earth

[slouper]

No big mystery, look like obvious mud cracks to me too.