Hg exists not only as cinnabar, but also as a liquid (there are seas of Hg in Spain). Cinnabar won't be found near lava, but in geological active zones (real lava would just burn it^^). But cinnobar isn't a material that is really needed in IC2. You could use it for mirrors too, but that's only the second use.
Aluminium is something more industrial and even there it is hard to find uses. Because normally you use most other metals for the same things you already use Iron etc. for. You could make Aluminium for cans instead of tin and it makes a good construction material, but we have steel and again iron (oh... and even bronze). So there is no real reason for such materials because they are already substituted by iron, steel, tin, copper and bronze.
The only thing I could imagine is a ore with just precious metals inside. This could be after some hard refining-process iridium or could be used as substitute for every rare materials like platin, zirconium or palladium... but again there is no real need for this materials. In reality we only use little amounts of them, using them in the crafting grid would create something that is created to 1/9 from this material... quite much. Most likely advanced circuits would include small amounts of zirconium or other precious metals and of course a little bit gold (... according to IC2 the gold is part of the glowstone-dust, so actually we use gold). But you don't use enough of this to make it worth it's own ore. Actually Zirconium and Niobium or Tantalum could be used for reactor-plating or other parts of reactors... but that's mainly the only use.
The truth and strangest thing is IF Mercury was not poisonous it would be an amazingly useful material. Every use I suggested for mercury is a real world use for it, excepting the fact that it isnt used for toxicity reasons. Beyond those reasons are a number of other lesser reasons that could still be effective.
http://www.glrppr.org/docs/mercury_in_industry.htm