Platinum for Thermal mods. | Feed the Beast
Likewise, if you DO find any platinum ore, you'll want to make the most of it - the pyro-concentrator augment for the Induction Smelter should (if memory serves) guarantee you one more ingot than you'd otherwise get - so in the case of cinnabar/rich slag smelting, instead of the usual 3 ingots of the main metal, you will get 4.