According to Nexus7 :
Hardness isn't really an issue. Heat resistance is.
According to my research, epoxy-bonded silestone (and Zodiaq) are relatively heat resistant - better than corian or plastic laminate - but the epoxies will burn or discolor if hot enough.
However, I get the impression that silestone and zodiaq are repairable to a certain extent, and we don't put hot pots on counters anyway.