re: "Clumping" issues
The clumping due to electrostatic charge is a possibility.
I did a google image search for "wheat flour" according to Nick's suggestion, and wasn't able to find anything at a close in scale. At the macroscale, the images I found don't resemble that clumpiness seen in the Phoenix microscope images. Admittedly though this is not definitive.
The Phoenix microscope images most closely resemble small clumps of moist soil, flecks of mud.
Then at least this possibility should be investigated in the simulated Mars soils to see if addition of moisture replicates the clumping and stickness seen in the soil at the Phoenix site.
Bob Clark