"Oh no!", I hear you say, "not that old chestnut again!"

Well, funny that you should use the word "Chestnut"...

Seems like just when you're getting to understand your beast, it changes colour on you! It appears that the white appearance of this particular white rock is a surface bleaching/weathering effect. if this rock is analagous to the other white rocks on Mars, then none of them are white, at heart.

We can play a bit with the colours. My favourite desaturated recipe yields:

- less red colour, but note the rich chocolate brown of the ratted areas (the white appears to be surface dust caught in cracks). The rock itself appears less blue than the full intensity version. (I have differentialy scaled down blue, btw, so this is expected)

Doug Ellison's recipe for "better" reds and blues (L3+L4)/2 = R, (L6+L7)/2 = B comes out like this:-

And desaturated as:

You pays your money and you takes your choice, but whichever wau you go, we're now looking at brown minerals, not white ones!

(geologists out there will not be surprised. It doesn't take much impurity or additive to a rock to completely change the colour of minerals, but it does mean we need a flick a few pages in our mineralogy texts...)