This "white" material is found all over Meridiani, usually in association with the dark material, which we see at the Opportunity landing site is neither sand nor dust. It appears to be of the consistency of talcum powder yet it seems to be very heavy. Very intriguing. I'll be delighted to see explanations.

The "white" stuff here strikingly resembles some of the "White Rock" outcrops found widely on the surface. Interestingly, no one has yet been able to identify what this material is. Some have confidently insisted that it is not carbonate material, based on very limited evidence -- actually an absence of affirmative evidence. The argument has been made that the dark stuff and the light colored stuff are actually the same stuff -- just different grain sizes. I doubt that argument is correct, but we don't know. It's the association of "white" material and this dark material that intrigues me. I hope we can learn some truths about both materials at the Opportunity site. I'm sure we will -- assuming the Martians don't get uppity and interfere again!

The resistance to accepting a limestone explanation for the "white" outcrops seems to be based on a deep antipathy to the notion that fluid water may have been active on/under the surface of Mars long enough to form carbonates. As long as the question is open, there will be those who insist that closing the door by argument rather than evidence is sufficient. Of course they are wrong. ;-)

I think it is important to let the evidence -- such as it may be --speak for itself and not try to "save the phenomena" for a particular hypothesis. Mars is obviously not like the Earth. There may be fewer similarities than we imagine.

Study on!

Cheers, BFelix