Ummm, the center electrode on Iridium plugs is, not surprisingly, made from... Iridium. Actually it's an alloy but mostly consists of Ir.
The part that won't last as long is the ground electrode. It's just a standard ground electrode, like you would find on a regular plug or single platinum plug. Actually I've read that NGK makes double Ir plugs for certain OEM applications, but it probably wouldn't fit the SC.