Mr. Mendeleev is your friend
http://www.bpc.edu/mathscience/chemistry/images/periodic_table_of_elements.jpgYour game seems pretty economy-focused, but that's at least original as military is most often stressed area.
I actually like mining and research most from your list, game focused this might be interesting (somehow
crossed my mind movie Outland, which I see very long ago and barely remember, but I think it took place on
Io's mining station)
Otherwise six resources seem to me quite enough...I think you can switch some of them as most of them are pretty similar by description
and purpose. Air came to my mind, that would be needed for atmosphereless planets (which could be rich in minerals and ore etc.)...
I actually think it's a good idea, the only game I've seen air used as resource was Submarine Titans, pretty nice PC underwater RTS.
Meh

I was happy that I'd come up with uranium and you already have that...but it could also be used for powering reactor that would provide
energy for a planet...that would add energy resource, though I'm not sure if it wouldn't be too similar to OGame....