Rover Finds New Mars Water Signs

The rover known as Opportunity has performed tests on a 30-cm long rock called Lion Stone, which most likely came flying out from the impact that created the nearby Endurance Crater. Concretions are found within thin fine layers, indicating that water most likely passed through the rock, allowing the concretion-material to precipitate out of the liquid water. The fine layering itself in the rock also appears to be deposited by water. These layers as well as the concretions can therefore give some insight into what the environment (most likely a water-type one) may have been like before the impact occurred that created the craters found in the area.

http://news.bbc.co.uk/2/hi/science/nature/3724493.stm