Cinnabar is a material added by Thermal Foundation. It can be obtained as a byproduct of processing Redstone Ore or, more rarely, Gold Ore in a Pulverizer.
Cinnabar can be used together with certain ore blocks in an Induction Smelter. When done so, the machine will produce three ingots as well as producing one guaranteed Ingot of whatever byproduct that ore has; if said byproduct is a kind of metal. This can be very useful for obtaining Shiny Metal from Ferrous Ore, or obtaining Ferrous Metal from Iron Ore.