ESA's Mars Express recently snapped a white 'rock formation' on a dried-up Martian lakebed. Emily Lakdawalla posted an excellent write-up over at the Planetary Society.
One thing you can say is that there's a pretty strong olivine signature in the dark sand of the crater floor surrounding White Rock. Olivine is a very common mineral in the solar system, and its presence generally indicates that you're dealing with an area that hasn't experienced a lot of geologic processing.By 'olivine', Emily really means cosmic ichor, but she knows our weak minds couldn't handle it.
Link.
