After looking at the raw images from the microscope in the last batch
posted on the rover website, I see what might just be visual artifacts, but
appear to be elongated structures. Some are hairlike, others are granular,
but there seems to be quite a few of them.
Have a look at this particular one (picked at random) and see what I
mean.

http://marsrovers.jpl.nasa.gov/galle...EFF0309P2930M2
M1.JPG

Now, about 20% from the left, near the top, there is a long, pale,
nearly vertical feature. from what they say about the image size and
resolution, it is likely about 0.1 mm in thickness. Similar ones appear
hear and there, mostly near the top of this particular image.
I think that it is possible that they are focal artifacts, caused by the
proximity of similarly lit or sized granules or clumps, and that since the
focus field is not flat, but much clearer in the image center, it might well
be the case. And statistically, there are going to be such things in many
images that contain many small, essentially random particles.
However, it is something worth looking into. Maybe I should get some
material that clumps in the same manner (cocoa, as they noted?) and try
getting some images through my microscope here. Might be informative.
Comments, anyone? Care to try an experiment? Oh, one question for Ron
Baalke- is this material undisturbed on the crater floor, or has it been
scooped into a container for examination? That, too, might have quite an
influence, such as causing "cracks" in the clumps, false alignments that are
not natural, etc.

Cheers!

Chip Shults