re: The clays on Mars.
Many possible minerals have been proposed to be the "missing" component of TES infra-red spectra. Glass (silica rich, silica poor, or alkalic varieties), sulphates, carbonates, clays, sheet silicates, etc.
Basically, nobody knows, and the data isn't good enough to be sure.
Clays HAVE been detected in the SNC meteorites in small concentrations, linked to localised ephemeral events.