"mlm" skrev i en meddelelse
...
Have a look at the structures in this image taken Thursday by Opportunity.
They look like what is left over when you pull the forms off a cement
slab.
Although incredibly fragile looking, they stand upright and are lined up
almost perfectly linearly. Reminiscent of the Easter Island sculptures in
miniature. Any idea what might have caused them. Perhaps a fracture from
the impact that formed the crater? Erosion by water or maybe sediment
caried by water and slapped up against a flat rock? It sees like they
were
up against something of different composition with a straight edge that is
now gone.

http://marsrovers.jpl.nasa.gov/gallery/all/1/p/162/
1P142569631EFF3221P2387L7M1-BR.JPG

It reminds me of a 'largescale' clayskins in gleyed soils.
I cannot make anything like it work with normal erosional/sedimentary
processes working on an open post-impact crack, and speculates weather the
fracture and the mineralisation or skin have formed before the impact.
Except for the origin of the crack, it should not pose a problem that the
destruction of the impact follows predefined weaknesses in the rock. I think
that it is reasonable to expect water, one way or the other, the mean of
transport of the minerals involved, but it still leaves an array of
posibillities. There is something in 'water', 'fine mars-dust' ( finegrained
smectitic clay in water) a crack and perhaps repeated wetting and drying
before water leaves for good that matches a developement of clayskin on a
ped (red iron on peds may also precipitate in else grey soil).
I do expect a mineralogist to post an alternative explanation though.
Someone used to mineralisations in veins may have a better key to the
problem.

Carsten