http://phys.org/news/2012-10-mars-curiosity.html#ajTabs
The rock is a mixture of insoluble salts from three acids.
Silicic acid provides the oxyanion SiO4 for the formation
of silicates such as olivine FeMgSiO4 and clay-feldspar
Ca(AlSiO4)2. Metasilicic acid furnishes the oxyanion SiO3
for the formation of pyroxenes FeSiO3 and MgSiO3;
metatitanic acid provides the oxyanion TiO3 for ilmenite
FeTiO3. Formation of the acids requires water under
pressure. Although shoreline volcanoes, such as Mt. Etna
and Kilauea, can provide the water and pressures, most
of these acids and rocks are formed at deep-sea
volcanoes at pressures ~250 atmospheres.
http://www.pmel.noaa.gov/vents/chemi...ges/vents2.gif
To achieve the same pressures, Mars' ocean had to be
more than ~6.65 km deep. Perhaps it's more than
coincidence that formation of fresh rocks takes place
at the same depth (pressure) as black smokers which
are invariably accompanied by biota under most inimical
conditions to life.
http://www.guardian.co.uk/science/20...ighereducation
John Curtis