http://en.wikipedia.org/wiki/Mercury_(element) just the idea sounds awesome, just to get it out there
Something like this has been asked before and I think the dev response was no, because we want metal planets to feel different.
It would be a neat addition for metal planets to be "able" to have seas and lava and metal planets be "able" to have a navy. Just make sure the default is that there isn't any on metal planets and by default there isn't enough useable lava to make naval in lava planets (a cosmetic amount could be not-navy-able if designed right). Only other problem is the devs have been saying "lava planets having real lava" has been setting back their usability ingame. That is a bother and would hate for that to hold development for release.
