Thanks for the reference Nick. Nice to see some real careful science rather than the drip-release of selected pseudo-science from the NASA PR machine. Interesting that no jarosite was found even with stongest acid conditions. The observation about anhydrite occurring as well as gypsum is also interesting as in evaporative sequences, anhydrite becomes the stable CaSO4 mineral once the activity of water in a concentrating brine falls far enough. This is soon after halite precipiation. There was also a mention of "fibrous" gypsum which remined me that gypsum forms with elongation along the c-axis in acid conditions. We find such crystals in many acid-saline systems within the southern half of Australia. If NASA wishes to claim vugs after gypsum in a jarositic rock, both anhydrite formation and elongated vugs must be accomodated in the model.