This may be of interest. An article from the BBC headlined “New Minerals point to wetter mars”, based on the Mars Reconnaissance Orbiter finding hydrated silica, and suggesting that it may been extensive and younger than previously detected. (At least I think that is what they are saying).
BBC
http://news.bbc.co.uk/2/hi/science/nature/7696669.stm

This is the abstract from the original article:-
abstract
http://www.gsajournals.org/perlserv/?request=get-abstract&doi=10.1130%2FG24967A.1

"Opaline silica in young deposits on Mars
Geology: v.36, p 847-50
R.E. Milliken1,*, G.A. Swayze2, R.E. Arvidson3, J.L. Bishop4, R.N. Clark2, B.L. Ehlmann5, R.O. Green1, J.P. Grotzinger6, R.V. Morris7, S.L. Murchie8, J.F. Mustard5, and C. Weitz9
High spatial and spectral resolution reflectance data acquired by the Mars Reconnaissance Orbiter Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument reveal the presence of H2O- and SiOH-bearing phases on the Martian surface. The spectra are most consistent with opaline silica and glass altered to various degrees, confirming predictions based on geochemical experiments and models that amorphous silica should be a common weathering product of the basaltic Martian crust. These materials are associated with hydrated Fe sulfates, including H3O-bearing jarosite, and are found in finely stratified deposits exposed on the floor of and on the plains surrounding the Valles Marineris canyon system. Stratigraphic relationships place the formation age of these deposits in the late Hesperian or possibly the Amazonian, implying that aqueous alteration continued to be an important and regionally extensive process on Mars during that time."